LABORATORY 1: KINGDOM PROTISTA
The Kingdom Protista contains the eucaryotic one-celled organisms. Until recently,
these organisms were generally placed in the phylum Protozoa within the animal kingdom.
However, since many of these organisms have definite plant-like characteristics as well as
animal-like characteristics, this old classification scheme has never been regarded as completely
satisfactory. The more recent idea is to place all one-celled eucaryotes in the kingdom Protista,
separate from the kingdom Animalia (multicellular animals) and the kingdom Plantae
(multicellular plants). The organisms in kingdom Protista are still frequently referred to as
protozoans. However, this term should be regarded as a common name and not a taxonomic
name. According to the classification scheme that we will follow in this course, the kingdom
Protista is divided into five phyla: Sarcodina, Mastigophora, Ciliophora, Sporozoa, and
It is important to remember that although protists are single-celled organisms, they are
still capable of performing all of the functions that multicellular organisms perform with their
many specialized tissues and organs. The functional diversity that protists exhibit within the
confines of a single cell make them truly remarkable organisms! Protists were the first
eucaryotes to evolve, and they are believed to have given rise to all other eucaryote organisms:
the multicellular animals, the multicellular plants and the fungi. As you will see in the
laboratory today, however, protists are far from simple or primitive.
Today’s laboratory will be roughly divided into two parts: 1) examination of the structure
and characteristics of the major protozoan groups; and 2) observations on the feeding,
reproduction, and osmoregulation of representative protozoans. If you are unfamiliar with the
operation of the compound microscope, read S&S 38-42, and ask for help. You will have to
make efficient use of your time today to finish the lab exercise properly.
A. PHYLUM SARCODINA - These protistans are characterized by their ability to produce
cytoplasmic extensions called pseudopodia. The pseudopodia are temporary in most cases and
are used both for locomotion and feeding.
1. Genus Amoeba- This is an excellent specimen to examine for general Sarcodine
anatomy. The outermost surface of these one-celled organisms is called the cell membrane or
plasmalemma. One of its primary functions is to regulate the movement of various substances
into and out of the cell. The cytoplasm enclosed by the cell membrane can be differentiated
into ectoplasm (the clear layer just beneath the cell membrane) and endoplasm (the largest
portion of the cytoplasm which is granular and fills the interior of the cell). These two
cytoplasmic regions have different consistencies, the endoplasm being less viscous than the
ectoplasm. Classical theories of amoeboid movement have generally referred to the endoplasm
as being a sol, to the ectoplasm as being a gel, and to pseudopod formation as resulting from
transformations between the sol and gel states. More recent theories avoid use of the terms sol
and gel, since even the endoplasm seems to have certain elastic properties not characteristic of a
sol. Taylor et al. (1973) propose that the ectoplasm and endoplasm of amoeboid cells
represent different states of contraction and relaxation of fibrils in the cytoplasm. These
contractile fibrils appear to be composed of thick and thin filaments which, in the presence of
calcium, form cross bridges and slide relative to one another (much as filaments in vertebrate
striated muscle do). Formation of a pseudopod is thought to occur as follows: At the tip of an
advancing pseudopod, free calcium ions are released. The increased calcium causes
contraction of the endoplasm as it everts to form an ectoplasmic tube. The ectoplasm at the
rear of the cell "relaxes" (loses viscosity) to become endoplasm and then is "pulled" forward into
the ectoplasmic tube of the pseudopod. Two other theories of amoeboid movement are
outlined in S&S, Fig. 1.15, p.16. Most of the organelles (functional units of the cell, e.g.
nucleus, contractile vacuoles, food vacuoles, mitochondria) are located in the less viscous
Observations of living Amoeba:
Study a specimen of Amoeba under a compound microscope. Amoeba are fresh water
organisms. Refer to Fig. 1.14A, p.16, of S&S as you make your observations.
a) Locate the endoplasm and ectoplasm and observe streaming cytoplasm if the organism is
b) How many nuclei does the cell have? What are several functions of a nucleus?
c) Observe food vacuoles within the animal. Despite their slow movement, Amoeba are able
to capture relatively fast-moving prey. Ciliates, for example, are an important part of the diet.
How do Amoeba catch their prey? What forms the membrane of the food vacuoles in Amoeba?
d) Locate a contractile vacuole. The activity of the contractile vacuole is normally much
higher in fresh water forms than in marine and endosymbiotic protozoa. This observation,
together with experimental evidence, suggests that the primary function of the contractile vacuole
is osmoregulation. You will experimentally examine the osmoregulation functions of
contractile vacuole later in today's exercise. What is osmoregulation? The contractile
vacuole was originally thought to be involved in the excretion of nitrogenous wastes. Does an
organism as small as an Amoeba really need an organelle to handle excretion? Why or why
2. Genus Difflugia- Members of this genus are structurally similar to Amoeba except
that they possess a one-chambered shell or test into which the entire cell may be withdrawn
(Fig. 1.24D, p.33 of S&S). The test of Difflugia is variable in shape and is composed of
foreign particles such as sand grains or diatoms, which are ingested by the organism and then
embedded in a secreted matrix.
What do you suppose is the function of the test of Difflugia? Difflugia live in a freshwater
environment. Would you expect to observe much contractile vacuole activity in this organism?
Why or why not?
3. Order Foraminifera- "Forams" are characterized by having perforated tests
composed of either calcium carbonate, silicon, chitin, or a gelatinous material. The test is
composed of two or more chambers (Fig. 1.24E, p.33 of S&S). The cytoplasm is not
differentiated into ectoplasm and endoplasm and it extends out through the pores of the shell as
well as through the shell aperture. Instead of ectoplasm, there is a solid fibrillar material in the
middle of each pseudopod. The cytoplasm flows along the fibers in a bidirectional pattern like
a conveyor belt. The pseudopodia in this group of Sarcodina form slender filaments which
freely branch and anastomose with one another. The Foraminifera are almost exclusively
marine, and upon death of the organisms the intact shells are added to marine sediments.
Foraminifera as such have been preserved in the fossil record since the Precambrium and are
important organisms for geological research. For example, they have been of considerable use
to the oil industry in identification of rock strata for drilling.
How would procurement of food by an organism with slender-branching pseudopods differ from
feeding in Amoeba?
4. Order Radiolaria- These organisms are similar to forams in possessing long,
slender pseudopods that radiate out from all sides of the organism. The major differences
between radiolarians and forams are:
a) Radiolarian pseudopods contain an internal supporting rod called a microtubule. The
microtubule functions in pseudopod movement in the same way that the fibrillar material does in
foraminiferan pseudopods. The main difference is in the actual structure of the microtubule as
compared with the fibrillar material.
b) Radiolarian skeletons generally have only one chamber. They are composed primarily of
silicon and are highly ornamented with lattice work, spines and hooks (Fig. 1.24C, p.32 of S&S).
Skeletons of the exclusively marine Radiolaria contribute to the formation of ocean bottom
sediments in the same manner as do foraminiferan shells, but to a lesser extent.
Would you expect foraminiferana or radiolarians to have particularly active contractile vacuoles?
Why or why not?
B. PHYLUM MASTIGOPHORA (Flagellata)- The flagellates are unicellular organisms
which possess one or more long, thread-like locomotory structures called flagella. The flagella
may be permanent or may appear only at one particular stage of the life cycle. Another
characteristic of flagellates is that during cell division, the plane of division is always parallel to
the long axis of the cell and is referred to as a longitudinal division. Because of the extreme
amount of diversity among flagellates, it is believed that the group is really polyphyletic and will
eventually be broken down into a number of separate phyla. At present phylum Mastigophora
includes plant-like forms containing chlorophyl which do not use flagella to any great extent,
actively swimming green flagellates, and actively swimming cells which lack photosynthetic
Flagella are usually as long as or longer than the cell body and are present in small
numbers. A flagellum is composed of a bundle of microtubules. (Fig. 1.2 and 1.7B, pp. 3
and 9 of S&S). The base of the flagellum is located within the cell and is called the basal body
or kinetosome. The microtubules in the shaft of the flagellum, which extend out from the cell
surface, are characteristically arranged so that one pair of central microtubules is surrounded by 9
pairs of peripheral microtubules. The entire shaft of the flagellum is covered by the cell
The movement of a flagellum during locomotion is extremely rapid and can only be
studied by means of high speed cinematography or stroboscopic techniques. Flagella generally
execute an undulatory motion. This undulation is either within one plane (producing a
sinusoidal wave) or in the form of a helix (resulting in a cork-screw-like motion). In either
case, the bending of the flagellum probably results from the sliding of microtubules in the shaft
relative to one another. The end result of flagellar movement is the creation of water pressure
which propels the cell through its environment.
The outer covering of many flagellates and all ciliates is called the pellicle. The term
pellicle refers to the presence of a more complex layer than the simple cell membrane of an
Amoeba. The rigid or semi-rigid pellicle helps maintain the structural integrity and
characteristic shape of these unicellular organisms. In addition, the pellicle provides a barrier
to diffusion of foreign materials into and cellular materials out of the cell.
1. Genus Euglena- This flagellate is commonly found in freshwater ponds and streams
and will be used in this laboratory to illustrate general flagellate anatomy. Observe a drop of
Euglena culture under a compound microscope. The live organisms are very small and move
rapidly. After observing the normal movement of the organism for a while, you may wish to
slow its movement by adding a drop of Protoslo to a drop of Euglena culture. As you work,
refer to Fig. 1.4A, p.6 of S&S. Because of the small size of live Euglena, you may have to
observe much of the anatomy from a prepared slide.
Observations of living Euglena:
a) The pellicle of the Euglena consists of the cell membrane and underlying fibrous elastic
protein and microtubules. The fibrous elastic protein provides flexibility, while the
microtubules give structural (or skeletal) support. When a Euglena stops swimming it may
undergo changes in shape as the cytoplasm flows and pushes against the pellicle. These
irregular changes in cell shape are referred to as metaboly. Look for such movements in your
specimens. The cell will return to its characteristic shape, probably by reordering microtubules
which were disordered during metaboly.
b) Note the green color of the cell. What causes this green color?
c) Notice the depression at the anterior end of the cell from which the flagellum arises. At the
base of the flagellum is a swelling which is thought to be a photoreceptor. Located in the
depression, directly opposite the photoreceptor, is a structure called the stigma (Fig. 1.4, p.6 of
S&S). The stigma is thought to function by intermittently shading the photoreceptor as the
Euglena rotates through the water. This enables the Euglena to determine both intensity and
direction of a light source. Do Euglena swim toward or away from light? Why do you
suppose they reacts as they do?
d) Would you expect a Euglena's contractile vacuole to have a relatively fast pumping rate?
Why or why not?
e) How does nutrition in a Euglena compare with that of an Amoeba?
2. Chlamydomonas, Pandorina, Eudorina and Volvox- These five genera of
freshwater flagellates will be discussed together because of the morphological similarities among
them. Chlamydomonas (Fig. 1.3, p.5 of S&S) is a very small unicellular organism possessing
two flagella, a nucleus, one large chloroplast, a stigma, contractile vacuoles and a cellulose cell
wall. The other four genera listed above all contain colonial flagellates. However, the
colonies are composed of individual cells which are structurally very similar to Chlamydomonas.
Examination of these colonies reveals an interesting pattern of increasing complexity in colonial
Gonium is composed of 4 to 16 cells which form a disc and are covered by a gelatinous
envelope through which the flagella protrude. In Pandorina 8 or 16 cells are closely packed in
a spherical colony which also has a gelatinous covering. A Eudorina colony contains 16 or 32
cells, arranged loosely in a hollow spherical or ellipsoidal shape, and covered with a highly
developed gelatinous mass. Another colony -Pleodorina - is similar to Eudorina but may
possess as many as 128 cells.
Finally, Volvox is the most highly developed form in this series of colonial flagellates.
A Volvox colony may contain from 200 to 2000 cells in smaller species and well over 10,000
cells in larger species. The cells are interconnected by cytoplasmic strands and form a hollow
colony filled with gelatinous material. (Fig. 1.5, p.7 of S&S).
There is more to this progression of colonial development than just an increase in cell
numbers, however. First, as the colonies become larger and more spherical there is a tendency
toward development of polarity in movement, so that the colony always moves with one pole
directed forward. Moreover, a division of labor among cells in the colonies becomes evident
with increasing colonial complexity. In Gonium, Pandorina and some species of Eudorina all
the cells in a colony are capable of reproduction. In more highly developed Eudorina colonies,
however, the 4 most "anterior" cells reproduce less often than the "posterior" cells. In
Pleodorina many of the anterior cells have lost the ability to reproduce. Finally, in Volvox most
of the thousands of cells in the colony are somatic cells and cannot reproduce. Only a small
number of reproductive cells, located in the posterior half of the colony, can carry on
reproduction. Volvox are capable of both asexual and sexual reproduction.
What are the functions of somatic cells in a Volvox colony?
What might this progression of colonial development mean in terms of the evolution of
Do you suppose that the flagella of colonial flagellates function in the same way as those of the
C. PHYLUM CILIOPHORA (Ciliata)- These protistans are distinguished by possessing
short, hair-like structures called cilia on the surface of the cell. In addition, all ciliates have two
kinds of nuclei: a larger vegetative macronucleus and a smaller generative micronucleus.
Also characteristic of ciliates is that during cell division, the plane of division is always
perpendicular to the long axis of the cell and is referred to as transverse division. The phylum
Ciliophora is characterized by great diversity. However, unlike the flagellates, all ciliates share
many significant features and so are considered to be one phylum.
The cilia of ciliates are morphologically very similar to flagella except that cilia are
shorter. They are also generally found in larger numbers rather than singly or in very small
numbers as are flagella. Various types of movement are exhibited by cilia. The most
common ciliary activity, however, is a beating motion which includes a stiff, rapidly sweeping
movement in one direction (the effective stroke) and a slower, highly flexed movement in the
opposite direction (the recovery stroke). The recovery stroke brings the cilium into position
for the next effective stroke so that the beating is rhythmically repeated. Individual cilia are
thus essentially acting like tiny oars. Since more water is moved by the faster effective stroke
than by the slow recovery stroke, pulses of flowing water are created which move from one side
of a cilium towards the other. If two cilia are located in close proximity to one another, their
movements will interfere as they both attempt to transport overlapping volumes of water. The
activity of two adjacent cilia must therefore by hydrodynamically coupled. (To what organisms
that you have already observed might this phenomenc also apply)?
Consider, for example, a long row of beating cilia. When a cilium at one end of the row
begins its effective stroke, this motion is passed to the next cilium in line. This second cilium
begins its effective stroke just slightly out of phase relative to the first cilium, and so forth down
the row. (Imagine a row of lined-up dominoes being knocked down in a chain reaction as a
result of touching the first domino in line). The result is the formation of metachronal waves
of beating cilia. More details of ciliary movement and theories of the mechanism underlying
ciliary coordination are beyond the scope of this course, but may be found in the references listed
at the end of this section.
As with the flagellates, the outer covering of ciliates is a pellicle. However the ciliate
pellicle is more complex than that of flagellates. It consists of three membranes: the cell
membrane itself (which extends over the cilia as well as the general cell surface) and the inner
and outer alveolar membranes (which enclose the fluid-filled alveolar sac).
1. Genus Paramecium- This freshwater ciliate will be used for a general study of ciliate
anatomy. Examine a drop of Paramecium culture first without and then with addition of a drop
of Protoslo (Fig. 1.8, p.11 of S&S).
Observations of living Paramecium:
a) In a Paramecium the pellicle is semi-rigid and maintains the characteristic shape of the cell.
You can study the surface features of the Paramecium pellicle by using the following technique:
Place a concentrated group of ciliates in as little water as possible on a clean microscope slide.
Add an equal volume of nigrosin solution and spread the mixture to a thin film. Allow this to
dry slowly and then examine the slide with a compound microscope. Notice the hexagonal
depressions on the surface of the cell. What are these depressions for? For observation of
structures other than the pellicle of the Paramecium use an unstained preparation or a preparation
stained lightly with methylene blue.
b) Note the oral groove which leads to the cell mouth or cytostome.
c) Observe the large macronucleus. How many micronuclei are present?
d) Do Paramecium have active contractile vacuoles? Food vacuoles?
2. Genus Vorticella- Refer to Fig. 1.16, p.19 of S&S.
Observations of living Vorticella:
a) A Vorticella is a sessile freshwater ciliate which is attached to the substrate by a stalk.
Within the stalk is a contractile fiber called a myoneme. Observe the periodic contractions of
the Vorticella stalk. It is interesting to note that the myoneme is completely covered by a thick
tube of cytoplasm and then by the cell membrane. The stalk, on the other hand, is extracellular,
being secreted by the cell but located outside the cell membrane.
Note that when the Vorticella stalk contracts, the whole cell responds as well. The
region around the cell mouth constricts and the cilia are tucked inside. Thus, it is obvious that
there are also myonemes associated with the main body of the cell and not just in the stalk.
b) The main portion of the cell is bell-shaped, with ciliation restricted to the region surrounding
the cytostome. Moreover, the cilia around the cell mouth do not function independently, but
rather are fused to form membranelles. Each membranelle consists of several short rows of all
of which adhere together to form a more or less rectangular structure which functions like a
single cilium. What is the function of these membranelles? What do you suppose is the
advantage of having fused cilia instead of individual cilia?
c) How does feeding in a sessile organism like a Vorticella compare with that of a motile species
like Paramecium? What are two major functions of cilia?
3. Genus Stentor- Refer to Fig. 1.12, p.14 of S&S.
Observations of living Stentor:
a) Stentor are large freshwater ciliates that spend much time swimming, but can also attach
temporarily to the substrate. When attached, Stentor are characteristically trumpet-shaped.
While swimming, it may assume a number of different forms. What allows Stentor to change
shape (Examine Fig. 1.12C, p.14 of S&S)?
b) The body of a Stentor is covered by rows of cilia. In addition, there is a row of fused cilia
(membranelles) located around the mouth region. What is the function of these membranelles?
c) What is the internal structure which looks 1ike a long string of beads?
d) Do Stentor have particularly active contractile vacuoles? Why or why not?
4. Genus Didinium
A Didinium is a barrel- shaped freshwater ciliate having a rounded posterior end and a
tube-shaped proboscis at the anterior end. The proboscis is capable of contracting and
extending and the cytostome is located at its tip.
Two rings of cilia are present on the organism, one located near the base of the proboscis
and the other near the middle of the cell. Didinium are voracious predators and feed on large
ciliates such as Paramecium. You may be able to observe predation of Didinium on
Paramecium by mixing one drop of each culture in a depression slide. Do Didinium make use
of cilia for feeding?
During adverse conditions (e.g., lack of food), Didinium form resistant cysts which have
been known to remain viable for up to 10 years. Excystment may be stimulated by the addition
of food to the encysted Didinium culture.
D. PHYLUM SPOROZOA- Members of this phylum lack special organelles of locomotion
(except for the microgametes which possess flagella). All members of this phylum are parasitic
and have very complex life cycles.
1. Genus Plasmodium- These Sporozoa produce the disease malaria. Four species
of Plasmodium infect humans, and related species occur in other vertebrates. The life cycle of
Plasmodium has 2 main phases. The sexual phase takes place within a vector or carrier, which
in this case is the Anopheles mosquito. The asexual phase occurs in the body of a vertebrate
host (e.g. a human). The invading Plasmodium destroy vertebrate erythrocytes and also cause
poisoning of the blood with breakdown products of red blood cells. These adverse effects
characterize the disease malaria.
E. PHYLUM CNIDOSPORA- The members of this phylum are also all parasitic. They all
possess resistant spores which are of unique structure. Each spore contains one to six
cnidocysts and one to many sporoplasms. The cnidocyst contains a long, fine tube coiled
within; its function unknown. The sporoplasms are small amoeboid individuals which emerge
from ingested spores and multiply within the host cell. Eventually they develop into new spores.
This phylum is poorly understood, due mainly to the small size of its members.
Cnidosporidans have been known to cause epidemics among such economically important
animals as silkworms, honeybees and commercial fishes. For example, Ich, a fatal fish
infection is caused by a cnidosporan.
Experiments and Observations of Protozoans
A. Feeding and Digestion:
The cilia of ciliates are used not only for locomotion but also to create water currents for
feeding. Food particles are swept into the oral groove and then to the cell mouth or
cytostome. The cytopharynx leads away from the cytostome and it is at the end of the
cytopharynx that food vacuoles are formed (refer to Fig. 1.8A, p.11 of S&S). The food
vacuoles are carried through the cell by endoplasmic streaming or cyclosis.
Although Paramecium may prefer to feed on bacteria, they will actively ingest yeast.
Yeast cells stained with Congo red dye are provided for you in this laboratory. Congo red is a
pH indicator which will change color between pH 5.0 and 3.0. The color of the indicator is
reddish-orange at pH 5.0 and above and it changes to blue as the pH approaches 3.0 and below.
As the stained yeast cells are ingested and their degradation progresses, it is possible to observe
food vacuoles containing material in various stages of digestion as shown by color changes of the
Place a drop of Paramecium culture on a slide and add a SMALL drop of stained yeast
cell solution. The color of the Paramecium and yeast mixture should be pink rather than red so
that observations will not be obscured. Support the coverslip with a small fragment of lens
How long after ingestion does a food vacuole form?
Do the streaming food vacuoles follow any special pattern in a Paramecium?
During what phase of digestion (early or late) are the food vacuoles most acidic? During what
phase of digestion are the food vacuoles most alkaline?
What happens to undigested material in Paramecium?
Why are food vacuoles formed rather than having digestion take place in the general cytoplasm
of the cell?
You may also want to examine the predatory behavior of Amoeba and Didinium on Euglena and
Paramecium, respectively. How does feeding behavior of these protozoans differ?
Many flagellates and ciliates produce complex structures in the cytoplasm which can be
wholly or partly extruded in response to certain stimuli. The trichocysts of ciliates were the
first such structures to be observed. In Paramecium the trichocysts are rod- or thread-like
organelles which are embedded in the ectoplasm and oriented at right angles to the cell surface.
Trichocyst discharge occurs within a few milliseconds and can be triggered experimentally by
chemical, mechanical or electrical stimulation. When completely discharged, a trichocyst
measures 20 to 30 microns, which is nearly 10 times its original length. The function of
trichocysts is still in question, although the most commonly suggested function is that of defense.
The example usually used in support of this is the release of trichocysts by Paramecium when
attacked by Didinium.
Place a drop of Paramecium culture on a slide and cover this with a coverslip. Place a drop of
acidified methylene blue to one side of the coverslip and draw it into the Paramecium culture by
placing a piece of paper towel at the opposite end of the coveralip. Observe the Paramecium
under high power with a compound microscope. The acid medium should trigger the firing of
How does the length of trichocysts compare with that of cilia?
Do some of the trichocysts separate completely from the pellicle?
Now that you know what you're looking for, expose some Paramecium to Didinium predators.
Examine interactions for the release of trichocysts.
Are trichocysts useful defensive weapons? What other possible functions, besides defense
could you suggest for trichocysts?
C. Mating Reaction and Conjugation:
Conjugation is a type of sexual reproduction common among ciliate protozoa in which
two individuals of the same species temporarily unite for the purpose of exchanging nuclear
material. Ciliates generally possess two types of nuclei. macronucleus, which is polyploid
and vegetative, disintegrates and is replaced during conjugation; the micronucleus is diploid and
carries the genetic information from one individual to another.
Many ciliates are known to have a number of mating types within each species.
Members of one mating type will conjugate with members of a different type but will not mate
with other individuals of their own mating type. The ciliate mating types are not comparable to
different sexes, however, since during conjugation a mutual fertilization occurs. In other
words, each individual functions like both male and female, retaining one gamete nucleus and
transferring the other to its partner. The mating type phenomenon can therefore be better
compared to devices used by other hermaphroditic organisms to ensure cross-fertilization.
In Paramecium, individuals of different mating types are morphologically identical.
How, then, does this ciliate recognize members of another mating type? Apparently, certain
chemical characteristics of the cell membrane surface are distinctive for specific mating types.
Physical contact between mature ciliates of complementary mating types will thus lead to
aggregation and attachment for conjugation.
Pure cultures of two mating types are available. Using a dissecting scope, observe each
mating type individually by placing drops of each culture into separate wells of a
multi-depression slide. Notice the avoidance reaction typical among members of the same
mating group. Now place a drop of each mating type together in the third well of the slide.
Observe the initial clumping reaction as members of opposite mating groups become attracted.
How soon after initial mixing of the mating types do conjugating pairs begin to break apart from
Where do members of a conjugating pair attach to one another?
Anderson, J.D. 1973. Amoeboid movement. In Comparative Animal Physiology. (ed. C.L.
Prosser). W.B. Saunders Co., Philadelphia, pp. 799-808.
Brown, F.A., Jr. 1967. Selected Invertebrate Types. John Wiley & Sons, Inc. New York.
Brown, F.A., Jr. 1973. Cilia. In Comparative Animal Physiology. (ed. C.L. Prosser).
W.B. Saunders Co., Philadelphia, pp. 809-821.
Grell, K.G. 1973. Protozoology. Springer-Verlag. New York. 554 pp.
Kudo, R.R. 1966. Protozoology. Fifth edition. Charles C. Thomas. Springfield, Illinois.
Leedale, G.F. 1971. The Euglenoids. Oxford Biology Reader No. 5 (eds. J.J. Head &
O.K. Lowenstein). Oxford University Press. London. 16 pp.
Satir, P. 1974. How cilia move. Scientific American 231:44-52.
Sleigh, M.A. 1973. The Biology of Protozoa. Edward Arnold Ltd. London. 315 pp.
Taylor, D.L., J.S. Condeelis, P.L. Moore, & R.D. Allen. 1973. The contractile basis of
amoeboid movement. The chemical control of motility in isolated cytoplasm. The
Journal of Cell Biology. 59:378-394.
Wodsedalek, J.E. 1965. General Zoology Laboratory Guide. Wm. C. Brown Co.,
Dubuque, Iowa. 264 pp.
LABORATORY 2: PHYLUM PORIFERA
The sponges are the first metazoans (multicellular animals) that we will study. The
principal features of phylum Porifera are listed below.
1. While some sponges are radially symmetrical, the majority of sponges are asymmetrical in
body form. Sponges are considered to be at a cellular grade of construction; that is, they have
cellular differentiation (tissues) without cellular coordination.
2. The outermost tissue layer of sponges is composed of cells called pinacocytes. In some
sponges this outer tissue layer is syncytial while in others the pinacocytes are all distinctly
separated from one another by cell membranes. The innermost tissue layer is composed of
cells called choanocytes or collar cells (see S&S, p.45) which have flagella that beat to produce
water currents through the sponge body. Between these two tissue layers is a gelatinous layer
called the mesoglea (mesohyl). The mesoglea is not considered to be a tissue since it contains
a number of different kinds of independently functioning cells. Each cell type in the mesoglea
has a specific name, but the general term for all of these wandering cells is amoebocyte.
3. Some of the amoebocytes in the mesoglea are specialized for secreting a skeleton. The
sponge skeleton may be composed of mineral spicules, spongin fibers or a combination of these
two, depending on the kind of sponge. Spicules may be calcareous (composed of Ca CO3) or
siliceous (composed of H2Si2O7). Spongin fibers are composed of a sulfur-containing
4. Water enters the body of a sponge by way of a number of minute incurrent pores or ostia.
Water leaves the body by way of one or more large excurrent pores or oscula. Within the body
of the sponge, the water may pass through a large cavity (the spongocoel) through a system of
canals and chambers, or through a combination of these two.
5. Movement of water through the sponge body is accomplished by the beating of the
choanocyte flagella. The choanocyte cells line either a spongocoel or a number of small
chambers, depending on the sponge. A choanocyte cell consists of a nucleus, one or more
vacuoles, a long flagellum and a delicate, collarlike structure which surrounds the base of the
flagellum. Electron microscope studies show the collar of a choanocyte to be composed of a
circular arrangement of microvilli-like structures extending outward from the cell body. The
rotary motion of the flagellum forces solid food particles in the incoming water to adhere to the
outside surface of the collar. The streaming protoplasm of the collar transfers the food to the
collar base where ingestion can occur.
6. Sponges may be divided into three basic grades or types based upon the arrangement of their
water canal systems. Note that these grades or types are not taxonomic groupings. The three
types of sponges are described below and are shown diagrammatically.
Asconoid Type - Water entering the sponge passes through ostia which are actually
openings within doughnut-shaped cells called porocytes, which are found only in asconoid
sponges. The water enters the large central cavity called the spongocoel, which is lined
with choanocytes. Water exits from the spongocoel through a single large osculum.
Syconoid Type - Water enters the sponge through ostia which are openings between cells,
rather than within cells as in asconoid sponges. Water then passes into radially arranged
incurrent canals which lead to flagellated chambers lined with choanocytes. Water leaves
the flagellated chambers by way of excurrent canals that lead to the spongocoel, which is
lined a simple flat epithelium. Water exits from the spongocoel by way of a single large
osculum. Note that the body wall of syconoid sponges is thicker than that of asconoid
sponges and that the syconoid spongocoel is not lined by choanocytes as is the asconoid
Leuconoid Type - The ostia of a leuconoid sponge are like those of a syconoid sponge.
These ostia lead into a complex system of canals and flagellated chamgers that penetrate the
very thick, dense mesoglea. There is no spongocoel in a leuconoid sponge. Rather, water
reaches the oscula by way of large excurrent canals. The complex canal system of
leuconoid allows for greater surface area over which water may pass and consequently creates
an increased area for food and oxygen uptake and for waste removal. It is not surprising,
therefore, that leuconoid sponges are the largest in size of all the types and that the vast
majority of sponges are leuconoid.
7. Sponge taxonomy is based on skeletal composition. The four classes in phylun Porifera are
listed below along with distinguishing characteristics for each class. The grades of sponges
found in each class are given in parenthesis, although this is not distinguishing since there is
overlap between the classes.
a) Class Calcarea - contains sponges having calcareous spicules with 1 to 4 rays.
(asconoid, syconoid, leuconoid)
b) Class Hexactinellida - contains sponges having siliceous spicules with 6 rays.
These spicules are often fused to form a beautiful lattice-like cylinder, as in the so-called Venus'
flower basket. (syconoid)
c) Class Demospongiae - contains sponges having siliceous spicules (not 6-rayed) and/or
spongin fibers. (leuconoid)
d) Class Sclerospongiae - contains sponges having an internal skeleton of siliceous
spicules and spongin fibers plus an outer encasement of calcium carbonate. Only six species
from the Caribbean have been described to date. (leuconoid)
8. Sponges are capable of both sexual and asexual reproduction and they also have great
powers of tissue regeneration and reassociation. Sexual reproduction is accomplished by
production of eggs and sperm which unite to form a zygote. The zygote divides repeatedly to
produce a free-swimming larval form. Depending on the sponge, this larva may be either a
uniformly ciliated parenchymula larva or an amphiblastula larva, which has flagella only at
one pole (Fig. 2.7, p.55 of S&S). The larvae eventually settle and metamorphose into the
Sponges may reproduce asexually by budding. In addition, all freshwater sponges and some
marine forms produce resistant overwintering bodies called gemmules. These gemmules
consist of aggregations of food laden amoebocytes surrounded by a resistant covering. They
are produced during periods of cold or drought and can survive to produce a new sponge body
when conditions improve (Fig. 2.8, p.55 of S&S).
In today's laboratory you will examine the structure of the sponge species available and
then perform experiments on the reassociation of porifera cells.
Asconoid sponges are the simplest and most primitive sponge architectural type and are
all relatively small due to their inefficient filtering system. Asconoid structure is demonstrated
in Leucosolenia. Obtain a small colony of Leucosolenia sponges and place it in a dish filled
with seawater. Examine it under a dissecting microscope. Does it respond to a stimulus?
Do you detect movement? To observe the filtering mechanism of Leucosolenia, prepare a
dilute suspension of carmine powder and seawater and then gently place a drop of the suspension
near the colony. Describe the water movement through Leucosolenia. Where do the carmine
particles enter? Where do they exit? Do particles enter the sponge at the same velocity that
they exit? Explain. Do you see budding on your Leucosolenia colony? If so, where are the
buds positioned? Examine the colonial structure of Leucosolenia. Describe how you think the
ultimate colonial form develops from a single sponge tube.
From your Leucosolenia colony remove a single sponge tube for closer examination and
then rinse the colony in fresh seawater and return it to the holding tank. Cut the sponge tube
longitudinally into two halves (from osculum to base) and place the two halves on a slide so that
half the tube shows the inner surface and the other half shows the outer surface. Add a drop of
saltwater and cover with a coverslip. Examine both surfaces under the compound microscope.
Try to identify porocytes, pinacocytes, and choanocytes, or evidence of their presence (refer to
S&S, pp. 45-47 for diagrams). Next, tease apart the sections of sponge with a dissecting
needle and examine for spicules and amoebocytes. Describe the shape and arrangement of the
spicules. How are spicules formed? Do you see any evidence of this in your preparation?
Examine the prepared slides of asconoid sponges. The staining of these slides will make the
cellular structures easier to identify.
Syconoid sponges are more complex than asconoid sponges. Syconoid sponges look like
large asconoid sponges, having a tubular shape, and each individual has a single excurrent
osculum. The body wall is thicker, however, and the spongocoel is lined with pinacocytes.
The choanocytes line finger-like chambers (radial canals), which permeate the spongocoel (see
pp. 50-51 in S&S). Because this arrangement provides a more efficient pumping system than
the asconoid design, syconoid sponges are larger than asconoid sponges.
Obtain a single specimen of Scypha, a representative syconoid sponge. How does the
colonial form of Scypha compare to Leucosolenia? Place your Scypha individual in a dish
filled with seawater and examine it under the dissecting scope. Does it respond to mechanical
stimulation? How does its filtration system compare to Leucosolenia? Section the Scypha
and examine its body wall structure. Examine the mesoglea and characterize the spicules of
Scypha (p.52 of S&S).
The prepared slides of a second syconoid sponge, Grantia, clearly shows wall structure,
choanocytes, and spicules.
Leuconoid sponges are by far the most complex architectural-type of sponge. Most
leuconoids are colonial, and although individual oscula can be distinguished, it is difficult to
separate individual members of the colony. The vast majority of sponges are leuconoid.
Examine the external and internal anatomy of the leuconoid available in the laboratory (probably
Microciona). How does its filtration system differ from the asconoid and syconoid sponges
you examined? Examine the body wall structure (see S&S, p. 51). Characterize the
SPICULE COMPOSITION AND STRUCTURE
The systematics of sponges are based primarily on the composition and structure of
spicules rather than on architectural plan. Spicules are composed of either calcium carbonate
or silicon dioxide, and the skeleton may consist entirely of collagenous fibers (spongin) or a
combination of spicules and spongin. See the introduction of this exercise (#8) for the
characteristics of the four classes of Porifera. The class membership of sponges is easily
determined using the following tests:
1. The organic matrix of sponges (spongin) dissolves when boiled in 5% sodium hypochlorite
solution. Place small pieces of sponge tissue in 1-2 ml of the sodium hypochlorite solution in a
testtube to carry out this test. Boil the mixture for a couple of minutes by placing the test tube
in a beaker of boiling water. After cooling, examine under the compound microscope. Are
spicules present? This technique is also used to remove spongin from spicules to examine
2. The inorganic chemical nature of spicules is determined by drawing acetic acid or dilute
hydrochloric acid under the cover slip of a wet mount of spicules. Calcium carbonate spicules
dissolve when treated in this manner, while silicon dioxide spicules are not influenced by the
3. Examination of the shape of spicules found in a sponge are also important taxonomic
characteristics (see S&S, p. 52, for representative spicule morphology).
Determine the class membership of the sponges available in the laboratory.
Sponges have remarkable powers of regeneration. A complete sponge can regenerate
from only a handful of cells. In the natural environment this means that when a sponge is
disturbed by a predator or physical disturbance, remaining fragments are able to form new
individuals and colonies. The impressive regeneration ability of sponges is due to the loose
organization of cells in individuals. Individual cells and unorganized clusters of cells are able
to reassociate and organize into new individuals. In today's laboratory we will examine the
reassociation phenomenon of sponges.
Procedure: Obtain a few milliliters of the suspension of Microciona cells available in
the laboratory. This suspension was prepared by pressing pieces of fresh Microciona through a
silk bolting cloth into seawater. Examine a drop of the suspension under a compound
microscope. It should consist of small clumps of cells.
Prepare a series of dilutions in seawater from the original suspension so that you have
samples of decreasing densities. Make your dilutions 100%, 50%, 25%, and 10% solutions of
the original suspension. Fill 2 small fingerbowls two-thirds full of cool seawater; place a
Syracuse watch glass on the bottom of each fingerbowl and put two slides on each watch glass.
Before placing the slides on the watch glasses, individually number each slide. Using a Pasteur
pipet, gently dispense equal aliquots ( 2 drops) of each suspension onto the slides. Place two
treatments (dilutions) on each slide and have all four dilutions represented in each fingerbowl.
Be very careful not to allow mixing of the dilutions on the slides. Be sure you record the
positions of the different dilutions on each slide. Clearly label your fingerbowls and have one
stand at 4C and the other at room temperature for 24 hours. After 24 hours, gently remove the
slides, cover with a coverslip, and examine under a microscope. Systematically count the
number of aggregates in each dilution and compare the size distribution of aggregates in each
dilution. Record all your data and observations. How do cell density and temperature
influence aggregation? What form do the aggregates take? How are different cell types
arranged in the aggregates?
Place a fresh drop of the Microciona suspension on a slide and examine it during the
course of the laboratory under l00X. Do you see any evidence of aggregation?
Following the procedures outlined above for examining reassociation in Microciona,
prepare similar solutions of a suspension of the cells of two sponge species (Microciona &
Haliclona). Prepare a fingerbowl incubating the four interspecific dilutions and let it stand for
24 hours at 15C. Compare these results with the Microciona suspension. What has
happened to the cells of the two species? How might segregation of the two cell types have
occurred? What other experiments could be performed to test this phenomenon further?
LABORATORY 3: CNIDARIA and CTENOPHORA
The phylum Cnidaria includes such animals as jellyfish, sea anemones, corals and
hydroids. This group was originally referred to as phylum Coelenterata, a name still seen in
many textbooks. Modern taxonomists, however, prefer the phylum name Cnidaria, and use
"coelenterate" only as a common name. Closely related to the phylum Cnidaria is the phylum
Ctenophora containing organisms called "comb jellies." Both cnidarians and ctenophores are
considered to be at the "tissue grade" of body construction. In other words, their body cells are
organized into tissues and these tissues are functionally dependent on one another, but (excluding
a few minor exceptions) these tissues are not organized into organs.
Cnidarians are radially symmetrical organisms that have one of two basic body forms: the
polyp form or the medusa form. Polyps are cylindrical in shape and are generally oriented in
the environment with their oral (mouth) surface directed upward and their aboral surface
(opposite the mouth) attached to a substrate. Medusae are umbrella- or bell-shaped, are
generally free-swimming, and are oriented in the environment with the oral surface directed
downward and the aboral surface directed upward.
The life cycle of cnidarians often includes an alteration of sexual and asexual generations,
a phenomenon that is referred to as metagenesis. When metagenesis occurs, the polyp is the
asexual generation and the medusa is the sexual generation. A generalized life cycle occurs as
follows: Medusae produce gametes which unite to form zygotes. Each zygote divides
repeatedly and develops into a free-swimming larval form called a planula larva (Fig. 3.17A
on p. 83 of S&S). The planula larvae eventually settle and develop into polyps. Each polyp
then asexually produces medusae to complete the life cycle. This generalized life cycle is
modified greatly in different groups so that either the polyp or the medusa stage may be reduced
or even completely absent from the life cycle. When the medusa stage is absent from the life
cycle, the polyp reproduces both asexually and sexually.
Colony formation is very common in the phylum Cnidaria, especially among polyps.
When colonies form, there is a tendency for individuals within the colony to become specialized
structurally and functionally. This structural and functional specialization within a colony is
referred to as polymorphism. You will be observing several examples of polymorphic
cnidarian colonies in the laboratory.
One particularly distinguishing feature of the phylum Cnidaria is that all members of the
phylum produce structures called nematocysts. Nematocysts are produced within cells called
cnidoblasts (or cnidocytes) and are discharged under the influence of mechanical, chemical or
nervous stimuli. Nematocysts function in defense, prey capture, and temporary anchorage of
the body to a substrate. After a nematocyst is released, its cnidoblast cell dies. New
cnidoblast cells and nematocysts are therefore continually being produced. The structure of
nematocysts and cnidocytes is shown in Fig. 3.13, p.75 of S&S.
Despite the difference in shape between polyps and medusae, the internal structure of
these two body forms is very similar. Each has a central coelenteron or gastrovascular (GV)
cavity which functions both in digestion and in circulation of nutrients around the body. The
GV cavity has a single opening to the outside--the mouth-- through which food enters the body
and undigested material leaves. The body wall consists of three layers: an outer epidermis of
ectodermal origin, an inner gastrodermis of endodermal origin, and a layer called mesoglea
between the two. The mesoglea is gelatinous in consistency and, in some cnidarians, may have
cells located in it. It is probably secreted by both the epidermis and the gastrodermis.
Most Cnidarians are carnivorous and use nematocysts to capture prey. The processes
of feeding and digestion are relatively uniform throughout the Cnidaria. Captured food is
passed into the mouth by the tentacles or by a tract of cilia. Digestion is partly extracellular and
partly intracellular. Extracellular digestion takes place in the GV cavity as enzymes are
secreted by gastrodermal cells lining the cavity. Finally, gastrodermal cells phagocytize the
partially digested food particles and digestion is completed intracellularly.
Both the epidermis and the gastrodermis absorb oxygen for respiration directly from the
environment or from the GV cavity. Oxygen then diffuses to any underlying cells. In the
same manner waste products, such as carbon dioxide and ammonia diffuse outward from cells to
the body surface. There are no specialized organs or body surfaces for gas exchange or the
elimination of wastes.
The phylum Cnidaria is divided into three classes based on characteristics such as life
cycle, the morphology of the GV cavity, and the presence or absence of cells in the mesoglea.
The three classes are Hydrozoa, Scyphozoa and Anthozoa.
In today's laboratory we will briefly examine the diversity of cnidarian form and life
styles and make observations on feeding, nematocyst function, and digestion in repesentative
organisms. In addition, we will observe a representative of the closely related Ctenophora.
The life cycle of hydrozoans typically exhibits metagenesis, alternating between an
asexual colonial polyp stage and a sexual medusa stage. However, within the class there are
species that tend to reduce either the polyp or the medusa stage of the life cycle. The
hydrozoan medusa usually has a circular shlef of tissue attached to the underside of the umbrella.
This structure is called the velum (see Fig. 3.1B, p.61 of S&S) and it functions in medusa
locomotion. In both polyp and medusa forms within class Hydrozoa, the mesoglea is acellular
and the GV cavity is a simple sac. One last distinguishing characteristic of the class is that
gonads are always formed from epidermal tissue.
In the life cycle of Gonionemus the medusa stage is conspicuous while the polyp is very
reduced. Each Gonionemus medusa produces either eggs or sperm, and the union of gametes
results in the formation of a planula larva. The planula grows into a minute solitary polyp
(about lmm in size) which asexually buds off other polyps. Each individual polyp then buds
off a free-swimming medusa to complete the life cycle.
Examine the diagram of a Gonionemus medusa in your text (Fig. 3.6A, p.68 of S&S).
Notice the velum. What do you think is the function of the velum? What is the function of a
In some hydrozoan species closely related to Gonionemus, the medusa stage is totally
absent from the life cycle. In these species the planula develops into a polyp-like larva called
an actinula (Fig. 3.17, p.83 of S&S). The actinula larva develops directly into a polyp.
The life cycle of this hydrozoan has a fairly even emphasis on the polyp and medusa
stages. The polyp stage of Obelia is colonial and provides a good example of polyp
polymorphism. Examine a live colony of Obelia under the dissecting scope. Rfer to p.71 of
S&S to identify polyp types. Two different structural and functional types of polyps can be
observed in the colony. The polyps with tentacles and mouths are called gastrozooids and their
function is feeding. The polyps without tentacles are called gonozooids and their function is
reproduction. Can you identify medusa buds within the gonozooids? These will eventually
give rise to free-swimming medusae. Often, by artificially manipulating the photoperiod of
marine organisms, it is possible to observe the release of planktonic stages. Observe a portion
of an Obelia colony which was kept in the dark for a couple of days and then exposed to light
just before the laboratory period. Have the gonozoids released medusa? If so, examine an
Obelia medusa. Why do you think this photoperiod regime would be expected to cause the
release of medusa?
All of the polyps of an Obelia colony share a common GV cavity so that food ingested by the
feeding polyps can be circulated to nourish the non-feeding polyps. Observe the transparent
skeleton covering the polyps of the colony. This covering is secreted by the epidermis and is
composed of a polysaccharide called chiton.
Hydractinia is a colonial hydrozoan which normally grows on snail shells occupied by a
certain species of hermit crab. Observe a living colony under the dissecting microscope. You
should be able to identify several different types of zooids. (Fig. 3.9 on p. 72 of S&S). The
gastrozooids have tentacles and mouths used in feeding. The spiral zooids or dactylozooids
are defensive in function. They are normally in a coiled position but can straighten out quickly
when the colony is threatened by a predator. The small knobs at the tips of these zooids are
reduced tentacles that contain batteries of nematocysts. Are the spiral zooids concentrated in
any particular area on the hermit crab shell? Why might this be so? The gonozooids
(reproductive polyps) bear several small swellings called medusoid buds. These medusoid
buds will never release free-swimming medusae. Instead, gonads will develop within the bud
and the eggs or sperm will be shed into the seawater. (Each colony bears either male or female
medusoid buds, but not both.)
What aspect of Hydractinia's life history might explain why the free-swimming medusa
stage has been lost in this organism? In colonial hydrozoans like Hydractinia and Obelia, into
what type of zooid do the planula larvae probably develop? Why? Speculate on the
relationship of Hydractinia and the hermit crabs which carry the shells they live on. What are
possible advantages and disadvantages (costs and benefits) to Hydractinia and hermit crabs in
this relationship? Would you describe this association as parasitism, commensalism, or
Although they are classically studied as "typical" cnidarians, Hydra exhibit several very
unique features. First of all, Hydra are freshwater organisms. This characteristic sets them
apart not just from other hydrozoans but from cnidarians in general. What structural
characteristic of cnidarians might account for the fact that the vast majority of cnidarians are
A second characteristic that distinguishes Hydra from other hydrozoans (and also from
scyphozoans) is that there is no trace of a medusa or even a medusoid bud in the Hydra life cycle.
Typically, Hydra polyps are reproduce by asexual budding throughout the spring and summer,
and they turn to sexual reproduction only in the fall. At that time, gonads develop directly on
the polyp. When Hydra eggs are fertilized, they receive a protective covering that makes them
resistant to freezing and desiccation. The eggs will develop into new polyps when
environmental conditions improve the following spring.
How might this reproductive phenomenon be correlated with the fact that Hydra are freshwater
A third unusual feature of Hydra relative to other organisms in its class is that Hydra
polyps are solitary rather than being colonial. The polyps do not secrete any type of skeleton,
and the individual animals are capable of considerable locomotion. Observe a living specimen
of Hydra and identify the structures labelled in Fig. 3.4, p.64 of S&S.
The reason Hydra are the standard cnidarian for study in the laboratory is because they
are generally available and cooperative in demonstrating a number of phenomena common to
cnidarian polyps. We will use Hydra today to examine polyp functions.
Obtain a few specimens of Hydra that have been starved for 48 hours and transfer them to
a syracuse watch glass containing pond water. Allow the animals to attach and relax and then
note how the body column elongates and the tentacles extend. Although Hydra are usually
sessile, they can glide on their base, float by means of gas bubbles secreted in the region of the
basal disc, and somersault to escape predators. These movements, however, are hard to elicit in
a laboratory situation. Using a probe, examine how different parts of a Hydra's body respond to
a stimulus. Are all parts equally quick to respond? What does this tell you about the nervous
system of Hydra?
With a pipet, transfer some Artemia larvae to the dish with the Hydra. Carefully
observe the reaction of Hydra to the prey. Describe the feeding response. Note the
movements of the tentacles and the reactions of the hypostome. What are the effects on the
prey? How are the prey held? Remove a prey item from the tentacles with fine forceps, make
a wet mount, and examine under high power of the compound microscope (use oil-immersion if
necessary). Examine and describe the nematocyst types found (p.75, S&S). To examine
undischarged nematocysts, remove a tentacle from a hydra with a forceps, place it on a slide,
cover with a coverslip, and examine under the compound scope. How are the cnidoblasts
distributed on the tentacle? To observe the discharge of nematocysts, draw 5% acetic acid under
the coverslip while observing cnidoblasts.
Let us now try to determine the mechanisms responsible for feeding behavior in Hydra.
Place a Hydra individual in a syracuse watchglass of water and attempt to discharge nematocysts
by mechanically stimulating a tentacle with a probe or strand of hair. Do nematocysts
discharge? Do you observe a feeding response in the individual? Now place isolated fresh
Hydra in a watchglass and examine their reaction to introducing clam juice and reduced
glutathione into the watchglass without applying mechanical stimulation. Reduced glutathione
is a chemical released by injured prey. Do the nematocysts discharge? Do you see a feeding
response? Construct a response-stimulus model of Hydra feeding behavior based on your
Physalia, commonly called the Portuguese man-of-war, looks like a large medusa but is
actually a floating hydrozoan colony (Fig. 3.10, p.72 of S&S). The float, which contains gas
and keeps the colony buoyant, is so highly modified that it is questionable as to whether it is a
polyp or a medusa. The float is the first member of the colony to develop and it asexually buds
off the other individuals of the colony. These other individuals are modified polyps and they
hang down from the lower surface of the float. Three different types of polyps can be
observed: gastrozooids, gonozooids and dactylozooids. Gastrozooids and gonozooids
function as described for other hydrozoan colonies. Dactylazooids each possess an enormous,
nematocyst-bearing fishing tentacle, and function in defense and in capture of food (although
food items must be passed to the gastrozooids for ingestion). As in other hydrozoan colonies,
the GV cavities of all members of the colony are connected. Examine the preserved Physalia
available in the laboratory.
This class includes the exclusively marine “true” jellyfish and their related polyps. The
medusa stage is usually large and conspicuous in the life cycle, while the polyps are small or
even lacking. The GV cavity in both the polyp and medusa forms is divided into 4 gastric
pouches. Medusa lack a velum and have oral arms (4 frilly extensions of tissue that hang down
around the mouth). Both polyps and medusae have a cellular mesoglea, and gonads on the
medusae are gastrodermal.
As a representative scyphozoan we will examine Aurelia, a common jellyfish found along
the Atlantic coast of North America. The life cycle of Aurelia is given on p. 63 in S&S. The
free-swimming medusae produce gametes which give rise to small polyps called scyphistomae.
After a period of growth, the scyphistoma divides transversely to become a strobila that
resembles a stack of discs. Each of the "discs" becomes an ephyra larva, detaches from the
strobila and swims freely in the plankton. The ephyra larva will eventually grow into an adult
medusa. Examine prepared slides of Aurelia planula, scyphistoma, strobila and ephyra and
locate the structures indicated in Fig. 3.3.
As was true for the Hydrozoa, scyphozoan polyps (scyphistomae) may asexually produce
other polyps in addition to producing medusae. New scyphistomae may be produced asexually
by budding or by producing structures called podocysts. A podocyst is formed when the basal
disc of the scyphistoma fragments off the parent polyp and becomes surrounded by a resistant
covering of chitin. The cyst will remain dormant for a while, but will eventually give rise to a
new polyp. Podocyst formation is seen in a number of different jellyfish species. Podocysts
are produced seasonally and are able to survive winter conditions that would kill the polyps.
Podocyst production may represent an adaptation to extreme environmental fluctuations. The
production of podocysts is thus analogous to the production of resistant eggs by Hydra.
Although scyphozoan medusae resemble hydrozoan medusae in general features, they
differ in that they lack a velum, they have a complex G.V. cavity, and they have compound sense
organs called rhopalia around the edge of the umbrella. In addition, the angles of the mouth
are elongated into four oral arms which are grooved, often frilled, and always heavily ciliated.
Examine a live specimen of Aurelia. Identify the oral arms, gastric pouches, rhopalia,
tentacles, and gonads. Refer to pp. 63 and 79 of S&S.
Carefully observe and describe the swimming movement. A single sadist in the class
may want to demonstrate the function of the rhopalia. How would you suggest this be done?
Examine the feeding response of Aurelia by placing one in a large fingerbowl filled with
seawater and then introducing Artemia larvae that have been in a suspension of carmine particles.
Describe the feeding behavior. Is capture passive or active? Examine Artemia that have been
captured by Aurelia and determine the types of nematocysts used. Allow the Aurelia to
continue feeding during the remainder of the laboratory period and at intervals note the
This remaining class of Cnidaria contains the sea anemones and corals. Medusae are
completely absent from the life cycle of anthozoans. The polyp produces gametes directly.
Fertilized eggs develop into planula larvae and each planula gives rise to a new polyp. In
addition to sexual reproduction, polyps may also reproduce asexually by budding or by
fragmentation. Anthozoan polyps may be solitary or colonial, depending on the group. The
internal structure of the anthozoan polyp is more complex than that of hydrozoan and scyphozoan
polyps. The GV cavity is characteristically divided by a number of radially arranged septa or
mesenteries (Fig. 3.5, p.66 of S&S). The mesoglea is always thick and contains cells and
fibrous supporting material. The gonads are gastrodermal and are borne on the septa. Most
Anthozoa have a bilateral or biradial symmetry superimposed on their basic radial symmetry
The Anthozoa are divided into two subclasses: 1) Zoantharia (Hexacorallia) - sea
anemones and hard corals; and 2) Alcyonaria (Octocorallia) - soft corals and horny corals.
The tentacles and septa are often in multiples of six but never eight. The tentacles are
always simple and the skeleton, if present, is an exoskeleton made of calcium carbonate.
Sea anemones are solitary polyps that usually live attached to a hard substrate. Sexual
reproduction in anemones occurs as described for Anthozoa in general. Asexual methods of
reproduction involve not only budding, but also fragmentation and fission. In fragmentation
small bits of the basal disc are cast off as the anemone slowly creeps along. Each bit grows
into a small anemone. Fission refers to the splitting of an individual longitudinally into a few
large pieces which become a new polyp.
In the laboratory we will examine the anemone Metridium as a representative anthozoan.
Obtain a Metridium specimen that has been allowed to settle on the bottom of a large fingerbowl.
The neuromuscular system of anemones is more highly developed and localized than that of
Hydra or Aurelia and can be examined in the laboratory easily. The anemone nervous system
consists of a two-dimensional neuronal net without ganglionic centers. Conduction is outward
in a circle from the center of stimulus, and the extent of the response depends both on the
intensity and duration of the stimulus. In addition to the nerve net there are well-developed
tracts containing elongate neurons which serve for rapid conduction (p.79, S&S). When your
Metridium is fully expanded, stimulate a tentacle by touching the tip with a probe. What is the
reaction? Is it localized? In what direction does the tentacle bend? Continue stimulating
the tentacle and/or increase the stimulus strength. (Don’t overdo it!) What happens? What
does this tell you about the nervous system of Metridium? Stimulate the body wall of the
anemone with the same intensity that you initially stimulated the tentacle. Is there a reaction,
what happens it you increase the strength of a single body wall stimulus? Explain these
To examine the feeding response of Metridium rub small clam fragments in powdered
carmine and present the food to the tentacles. What is the response? Does the response differ
with the size of the introduced food? Are nematocysts used in the capture of the prey? Be
frugal in feeding your anemone so that it will cooperate with your remaining observations.
Place a small piece of stained food on the edge of the oral disc. How is the food moved toward
the mouth? Do tentacles move the food into the mouth? Can you observe the activity of
acontia at the base of the actinopharynx? What is their function? Try feeding your anemone a
piece of wet filter paper. What happens? Next try feeding your anemone filter paper which
has been wetted by absorbing fluid from clam tissue. Is there a difference in response?
Since the food you are using to feed your anemone has been "stained" with carmine
particles, you should be able to trace the path of the food into the coelenteron. Try to document
that the food is directed down the actinopharynx by the flagellated siphonoglyph, and inside the
coelenteron by cilia on the septa. The thin septa ensure that the living tissue is nowhere very
thick and diffusion paths of food and gases remain short. The actual site of digestion of food
by Metridium may be determined at the end of the laboratory period. Allow the Metridium you
have fed carmine stained food to stand in fresh seawater in the cold room until close to the end of
the laboratory period. Then relax the fed specimens in 7.2% MgC12 and open the coelenteron
by making a longitudinal incision from the base to the oral disc. Try to locate the structures
diagrammed on pp. 66 and 79 of S&S. Where is the food located? Can you observe whole
carmine particles in cells? Does digestion take place extracellularly or intracellularly?
Examine a cross section of your Metridium and locate the following: pharynx,
siphonoglyph, complete and incomplete septa, GV cavity, retractor muscles, gastrodermis,
mesoglea, and epidermis.
The fundamental anatomy of the septa and the GV cavity of hard corals closely resembles
that of sea anemones. The major differences involve the colonial growth pattern of most corals
and the secretion of a massive calcium carbonate exoskeleton. Examine a colony of living
Astrangia and identify the basic external features of the polyps.
In the most generalized coral skeleton type, the portion of the exoskeleton directly around
the polyp resembles a cup with a floor and walls. Astrangia forms this type of exoskeleton.
Soon after the planula larva settles and becomes a juvenile polyp, it begins forming an
exoskeleton by secreting the floor of the coral cup. Almost at once the undersurface of the
polyp develops radial folds which secrete radially arranged ridges called sclerosepta. These
skeletal sclerosepta alternate with the tissue septa within the GV cavity of the body. At the
same time a rim is formed and built up as a wall around the polyp. Study a piece of Astrangia
(or other cup coral) from which the polyps have been removed.
The exoskeletons produced by other coral types are modifications of the
floorwall-sclerosepta pattern seen in the cup corals. One interesting modification is seen in the
mushroom coral, the only solitary coral polyp that you will study in the lab. Note that the large
individual polyp that secreted this skeleton produces a floor and sclerosepta but no walls.
Thus, the skeleton is relatively flat instead of being cup-shaped. A second modification is seen
in the colonial rose coral and in brain corals. Here the polyps are arranged in rows, and
adjacent polyps in a row are fused to one another. These polyps secrete a common wall around
the whole row of polyps without producing walls between neighboring polyps. The result is
the formation of a series of winding grooves on the surface of the calcareous skeletal mass.
Are sclerosepta obvious in this type of coral configuration?
You should also take note of the great variety of overall shapes that entire coral colonies
may acquire. Some corals produce lateral branches, while others are encrusting or leaf-like.
Still others form large compact mounds. The overall shape of the colony is determined by the
pattern in which new polyps are asexually budded.
This subclass includes sea fans (gorgonians) and sea pens (Renilla). They are always
colonial. Each individual polyp of the colony has eight pinnate (feather-like) tentacles, eight
complete septa and a single siphonoglyph. Note that the mesoglea of alcyonarians is relatively
thick. Running through the mesoglea are numerous gastrodermal tubes that connect the GV
cavities of individual polyps in the colony.
The alcyonarian skeleton is an internal one or endoskeleton which is secreted by the
mesoglea. It is generally in the form of microscopic spicules of calcium carbonate. However,
the horny corals -- sea whip and sea fan -- have an endoskeleton of horny protein material in
addition to spicules. This horny skeleton is important in giving support to the colony. The
skeleton of another alcyonarian, the organ pipe coral, is particularly interesting. This skeleton is
composed of fused spicules stained red with iron salts. The spicules are secreted by the
mesoglea, but they end up encasing the polyps of the colony. The skeleton is built into a series
of tubes (each of which contains one polyp) strengthened by connecting transverse platforms.
In several groups of Alcyonaria there is polymorphism of individuals within a colony.
This is illustrated nicely by the sea pansy and the sea pen (Fig. 3.11, p.74 of S&S). The sea
pansy consists of a large primary polyp with a stem-like base that is anchored in the sand. The
upper part of the primary polyp gives rise to two types of secondary polyps. Autozooids are
ordinary polyps which bear tentacles, feed and reproduce. Siphonozooids lack tentacles, are
small and wart-like in appearance, and occur in clusters. They do not feed, but rather serve to
create a water current through the colony. What is the function of this water current?
The Ctenophora are among the most beautiful of marine organisms. They are
transparent, pelagic animals with bilateral symmetry superimposed on a basic radial symmetry.
They are never colonial and have no sessile stage. Their most characteristic features are ctenes,
which are plates of fused cilia arrangea like the teeth of a comb (see p. 172 Barnes). There are
eight vertical rows of ctenes arranged at intervals around the body. The ctenes in each row beat
in metachronal waves and propel the organism's mouth forward through the water. Examine
the locomotion of a live specimen of Mnemiopsis (if available) under a dissecting scope in a
Like Cnidarians, all ctenophores are carnivorous and may use tentacles to capture food.
Only one species of ctenophore produces nematocysts. All other ctenophores have colloblast
cells, which function in food capture by sticking to prey items.
Discharged colloblast cell
Introduce some Artemia marked with carmine to the Mnemiopsis and observe prey
capture. Remove a captured Artemia and examine for colloblast fragments.
Apart from the recent discovery of true nematocyst in one ctenophore species, many
things indicate a close relationship between ctenophores and cnidarians. These include: 1) the
properties of the cells of the mesoglea, 2) the nature and organization of the GV cavity and nerve
nets, 3) the general tetraradial symmetry, and 4) the lack of organs other than sensory ones. In
addition, at least one species of ctenophore has a planula-like larval stage.
TERMINOLOGY TO KNOW FOR PHYLA CNIDARIA AND CTENOPHORA
Since the cnidarian/ctenophora section includes a large number of terms, we thought it
would be helpful to highlight the most important ones for you. You should be able to give a
good definition or description of all the terms listed below. You should also know the function
and location of any anatomical structures in the list.
coelenteron (gastrovascular cavity)
basal disc (pedal disc)
complete septum or mesentery
incomplete septum or mesentery
HYDROZOAN LIFE CYCLES
Zygote Ciliated larva (Planula)
Life Cycle of Obelia
Metamorphosis and settling
Budding Hydroid Colony
A. Tendency for reduction B. Tendency for
of medusa stage. of polyp stage.
Polyp Eggs and sperm Medusa Eggs and sperm
Actinula larva Planula larva
Life Cycle of Hydra Life Cycle of Some Close Relatives
LABORATORY 4: PHYLUM PLATYHELMINTHES
The phylum platyhelminthes is composed of three classes: the free-living (i.e.
nonparasitic) TURBELLARIA, and two classes of highly specialized parasites, the
TREMATODA (flukes) and the CESTODA (tapeworms). Generally, the term “flatworm” is
restricted to the class turbellaria, in spite of its being the common name of the phylum. Flukes
and tapeworms, along with certain other groups of parasitic worms, are commonly called
helminthes, a convenient nontaxonomic term for worm parasites.
The platyhelminthes demonstrate remarkable adaptations to both a free-living intertidal or
fresh water existence, and a parasitic mode of life. The phylum also displays: 1) the organ level
of complexity, 2) bilateral symmetry, and 3) the simplest type of body organization built largely
of mesoderm. These three characteristics are critical steps in the development of complex
Certain characteristics of free-living flatworms have suggested to some workers that
platyhelminthes are ancestral to the more complex animal phyla, and hence to all animals of
greater complexity than a jellyfish or sea anemone. The increased specialization of mesoderm
with the development of efficient organs is the most marked distinction between flatworms and
jellyfish or sponges. Turbellaria are the simplest animals with a brain and central nervous
system (CNS), a well-organized excretory-osmoregulatory system, and a complex reproductive
system. Most body functions of flatworms are performed by specialized tissues or organs; a
significant difference from the most complex cnidarians in which organs are more or less absent
and highly specialized individuals (zooids) accomplish feeding, reproduction, defense, and other
Accompanying bilateral symmetry in flatworms is cephalization which is associated
with improved sensory perception, increased muscular coordination, more rapid movement, and
greater efficiency in food processing, excreting wastes, and controlling metabolic processes.
Associated with greater structural complexity is a pattern of life employing a
CNS-directed mobility in the active seeking of prey. This is a distinctly different pattern of
behavior from that of coelenterates which sting prey accidentally encountered in their primarily
nondirected swimming, floating, or sessile activities.
To understand the factors permitting increased complexity in invertebrate phyla, the
structural development of mesoderm tissue and body cavities is important. In platyhelminthes,
mesoderm fills the space between body wall and gut (the potential body cavity space) with a
mass of cells lacking clearly defined cell membranes. The platyhelminth organization,
considered the most primitive type among higher animals is called acoelomate (without a true
coelom). Further integration of organ systen is found in the phylum ASCHELMINTHES
where a body cavity is partially lined with mesoderm. This body plan is termed
pseudocoelomate. In animals possessing a true coelom (coelomates) structures lying between
the body covering (epidermis) and intestinal layer (endodermis) are enclosed by mesodermal
sheets called mesenteries, and in these animals specialized and discrete organs are individually
enclosed in a mesodermal lining and suspended within the body cavity.
In today's laboratory we will examine structure and function in the three platyhelminthes
These are the free-living flatworms that have a ciliated epidermis with rhabdites and mucus
glands and a ventral mouth. They are usually pigmented and have eye spots. The orders of
turbellaria are based on the structure of the digestive system and are: 1) Acoela (no digestive
tract); 2) Rhabdocoela (single digestive tube); 3) Alloecoela (straight digestive tube with short
branches); 4) Tricladia (three-branched digestive tube) and 5) Polycladia (manybranch, mostly
marine forms). We will examine the common freshwater Dugesia as a representative
Examine a living specimen of the common freshwater planarian Dugesia in a watchglass
containing pond water. Identify the external structures diagrammed in S&S, p. 95. Can you
identify the anterior end? What structures are associated with the anterior end? To examine
the ventral surface of Dugesia, lightly ring a coverslip with petroleum jelly, place a drop of water
or two and a planaria on the coverslip, and then lightly press a second coverslip over the first.
If done carefully, you can use this mount to examine either side of Dugesia. Observe the
ventral and dorsal surfaces carefully. How do they differ? Identify the structures on the
To examine the internal anatomy of Dugesia examine a prepared slide of a cross section.
Refer to S&S, p. 96. Notice the single-layered, cellular epidermis in some species the
epidermis may be syncytial (multinucleated). Characteristic of the epidermis of turbellarians
are rhabdites, which are curved rods embedded in the epidermis. Little is known about the
function of rhabdites. However, since they discharge to the exterior when the animals are
stressed, a protective function is suggested. Try to locate small regions of dorsal surface devoid
of rhabdites and cilia on the margins of the body. These are the locations of adhesive glands,
whose secretions aid the animal in adhering to the substrate. Locate the following structures on
your slide: gastrovascular cavity, gland cells, mesenchyme, nerve cord, circular muscles,
longitudinal muscles, and pharynx. Why might you not be able to find all these structures?
Try to locate the cerebral ganglia of Dugesia on the specimen you have sandwiched
between coverslips. If it is dried or otherwise damaged, prepare a new setup. Locate as many
CNS structures as possible.
The coordinating function of the nervous system of flatworms is most easily studied by
observing behavior. With a paintbrush, transfer a living specimen of Dugesia to a watchglass
and observe its movements. Using a probe examine the reaction of Dugesia to physical
stimulation. Is Dugesia equally sensitive to mechanical stimulation throughout its body?
Carefully examine the locomotion of Dugesia and describe how you think it is accomplished.
How and what muscles are used? How are cilia used? The relative roles played by cilia and
muscles in locomotion may be determined by treating individuals with a solution of 1 to 2%
lithium chloride, which inhibits ciliary action, or with a solution of 1-2% magnesium chloride,
which paralyzes the muscles. Explain your results. What do you think the role of mucus
glands is in locomotion? To observe mucus tracks, add some talcum powder to a dish of water,
mix well and allow the suspension to settle to the bottom of the dish. Pour off the water.
Transfer a fresh planarian to the talc suspension dish and note the tracks produced by the
We will now attempt to examine the conditioning of behavior with Dugesia. Expose a
Dugesia in a watchglass to a strong directed light (use the dissecting scope light). What is the
reaction? Are Dugesia photonegative or photopositive?
The digestive tract of turbellarians (except acoels) consists of a midventral mouth, a
muscular pharynx, and a blind-end intestine. As mentioned previously, the branching
arrangement of the gastrovascular cavity is the main basis for separating the free-living
flatworms into orders. Examine the branching patterns of the turbellarian slides available to
you in the laboratory. To examine the feeding process in Dugesia, place starved individuals in
a large watchglass of water. Place them in the middle of the container, and then introduce
small bits of fresh liver on one edge of the container. Do the Dugesia move directly to the
food? Patiently examine the prey searching and feeding behavior of Dugesia. Describe what
Turbellarians have simple life cycles, particularly by platyhelminthes standards.
Turbellarians, however, have considerable powers of asexual reproduction. Some species of
Dugesia rarely reproduce sexually, but commonly reproduce asexually by transverse fission.
Dugesia are unusual in that the sexual reproductive system appears only during the spring and
summer months when it sexually reproduces. Like almost all flatworms, Dugesia are
Examine a whole stained mount of Bdellouria on which you should be able to identify
parts of the reproductive system. Refer to S&S, page 108.
If time permits, you may want to examine the regeneration ability of flatworms. Follow
the directions given in S&S, pp 110-111 with the following exception. To cut a Dugesia allow
it to extend itself on the flat surface of a moistened cork and then using a single-edged razor
blade, make your cuts in a single motion while observing under a dissecting microscope. You
can examine the results during next week's laboratory period.
These are the flukes which are: all parasitic, have an external tegument, suckers and/or
hooks for attachment, anterior mouth leading into a two-branched digestive tract, and single
ovary and paired testes. There are two orders: 1) Monogea (usually single host with direct
development, i.e., no distinct larval stages), 2) Digenea (more than one host, one of which is
always a mollusc).
Examine a prepared slide of the human liver fluke Clonorchis. Refer to p. 96 of S&S.
This flatworm lives in the bile ducts of humans and feeds on the living tissues of the host. The
anterior end of the worm tapers to a point and bears a sucker at its tip, whereas the posterior end
is blunt. Is Clonorchis bilaterally symmetrical? The oral sucker at the anterior end
surrounds the mouth. Note the two branches of the gastrovascular cavity. As in all
helminthes the reproductive structures take up most of the body space. These parasites have
essentially become reproductive machines; since the chance of a parasite individual to transfer its
progeny from one host to another is remote at best, high reproductive capacity is an essential
adaptation for survival. Can you observe any difference between the dorsal and ventral
surfaces of Clonorchis? How does this compare with Dugesia? Suggest an explanation.
Now examine a cross section of Clonorchis and identify the structures shown on S&S,
page 96. Pay particular attention to the body covering or tegument, which was lacking in
Dugesia. What is the function of the tegument?
In order to examine living trematodes, we will attempt to find the frog lung fluke,
Haematoloechus, in the lung of the leopard frog, Rana pipiens (See pg. 101 in S&S). Your
T.A. will dissect out the lung from infected frogs and place them in frog ringer's solution.
Usually the small brown, black, and white mottled flukes will emerge on their own, although
some teasing apart of the lung may expedite the process. Transfer one of the flukes to a
watchglass with ringers solution, and examine the movement of the flukes. Are cilia involved
in locomotion? Are the suckers involved in locomotion? What effects do solutions of
lithium chloride or magnesium chloride have on trematode locomotion? How does the
structure of Haematoloechus differ from Clonorchis?
The reproductive system of trematodes differs from that of turbellarians chiefly in the
enlargement of the main canal of the female system into a coiled uterus, capable of storing many
fertilized eggs. Reexamine a whole mount of Clonorchis and identify the male and female
components of the reproductive system. See p. 96 of S&S. While self-fertilization appears
to occur in trematodes, cross-fertilization is the rule. Copulation involves the insertion of the
penis or cirrus into the terminal portion of the Laurer's canal or uterus of another fluke. Sperm
are stored in the seminal receptacle and released when required.
In contrast to the above description of hermaphroditic trematodes, flukes in the family
Schistosomatidae live in the hepatic portal system of birds and mammals and are noteworthy
due to their sexual dimorphism. Schistosome parasites are extremely common and dangerous
parasites of humans and infect hundreds of million of people annually. Examine the
schistosome slides on demonstration in the laboratory.
As mentioned previously, the two classes of trematodes are characterized by different life
cycles. The monogens are ectoparasites and have only a single aquatic, cold-blooded host and
have direct development with no asexually reproducing larval stages. The diogens are largely
endoparasites and have at least two hosts and asexually reproducing larval stages.
Examine the typical diogenetic life cycle illustrated in S&S on page 105. Typically, the
sexually reproduced egg hatches to a ciliated, free-swimming miracidium, which penetrates the
body of an invertebrate (usually a snail) and becomes a sac-like sporocyst. By a sexual
reproduction, the sporocyst gives rise to generations of rediae and/or cercariae. The latter
have tails, and, on their release from the snail they swim, find, and penetrate their vertebrate host.
In some species, the cercariae encyst on an additional host or vegetation as metacercariae and
enter the vertebrate host when ingested. Be sure you examine and understand the life cycles
outlined at the end of this handout and examine the demonstration slides of different trematode
These are the tapeworms which are: parasites on vertebrates; usually intestinal; usually
segmented, with each segment (proglottid) lined with tegument and bearing one or two complete
hermaphroditic reproductive systems; anterior scolex with suckers or hooks for attachment; no
digestive system or sense organs; and the life cycle is complex with no larval multiplication in
Examine a preserved specimen of the pork tapeworm Tacnia solium, which shows the
typical morphology of this class of flatworms. Refer to page 98 of S&S to identify the
structures you see. The body consists of a linear series of proglottids that become
progressively smaller, so that the most anterior tip of the animal consists of a microscopic scolex.
Study the scolex under the dissecting microscope and note the attachment structures.
Immediately posterior to the scolex is the neck, which buds off proglottids which contain the
male and female reproductive machinery. Tapeworms do not have a digestive track.
Examine a prepared slide of a cross-section through a Taenia proglottid. Note the
heavy tegument on the proglottids (pp 98, S&S). What is the function of this covering? Is
the body surface ciliated? Try to identify the internal structures of proglottids diagrammed in
Fig. 4.3 of S&S.
Like flukes, tapeworms are hermaphrodites. Each mature proglottid of a tapeworm
contains at least one complete set of reproductive organs (male and female). Identify the
structures of the male and female reproductive system on a prepared slide of a mature proglottid
referring to the diagram on p. 98 of S&S. Immature proglottids are produced immediately
behind the scolex and initially do not show developed sexual structures. You should be able to
observe this on the prepared slides of a Taenia scolex. As the proglottids mature, their
reproductive structures become evident. As in flukes, eggs from the ovary move down the
oviduct and into the yolk duct. Sperm, having entered the vagina after copulation, migrate
from their storage point in the seminal receptacle, through the oviduct and into the yolk duct
where fertilization occurs. Eggs are then quickly coated with yolk and a shell. Finished eggs
are then pushed along into the uterus. In the uterus the eggs develop into larva still in the shell.
The larva hatches from the shell after being stimulated to do so in the stomach of an intermediate
host, which became infected by accidentally ingesting eggs or segments from the feces of the
previous host. The released larva then penetrates the intermediate host's intestinal wall, invades
the body tissues, and forms cysticercus (bladder worms) in muscle or other tissue. See p. 106
of S&S for a diagram of pork cysticerci. Examine a prepared slide of the cysticercus larva.
How does the final host become infected?
Tapeworm life cycles are complex and variable and you should be sure to examine all the
demonstration material on these life history patterns which will be available in the laboratory
LABORATORY 5: THE PSEUDOCOELOMATES
The pseudocoelomates are a diverse group of organisms that are grouped together in the
phylum ASCHELMINTHES by some authors. In our work, however, we will consider each
pseudocoelomate group to represent a separate phylum instead of classes within the phylum
Aschelminthes. Using this approach, the terms pseudocoelomate and aschelminthes are
descriptive terms with no taxonomic meaning. The pseudocoelomate phyla are Nematoda
(round worms), Rotifera (wheel animalcules), Gastroticha, Kinorhyncha, and Nematomorpha
A number of common characteristics among these groups justifies considering them
together. The pseudocoelom is one important characteristic shared by all these groups. The
pseudocoel is a space between the intestine and body wall which is embryonically derived from
the blastocoel and is filled with fluid and the reproductive and excretory systems. It is believed
that the pseudocoelom represents an evolutionary stage between the acoelomates, in which the
body cavity is filled with undifferentiated mesodermal cells, and the coelomates, in which the
body cavity is completely lined with mesoderm. What are the advantages of a coelom?
A second major difference between the pseudocoelomate phyla and the phyla we have
considered thus far is the presence of a complete digestive system: mouth => intestine=> anus.
Cellular specialization in this system allows ingested food to be processed along a one-way
passage, with unassimilated matter being ejected out the anus, rather than having it returned and
passed back out the oral opening as in cnidarians and most platyhelminthes. The advantage of
a one-way digestive system should be obvious.
Pseudocoelomates also possess a hardened cuticle. The cuticle is not only an
extraordinarily effective protection against harmful external substances (or digestive enzymes in
the case of internal parasites), but also serves as an exoskeleton, allowing an extensive area for
muscle attachment and support.
Still another remarkable characteristic of pseudocoelomates is a tendency towards
constancy of cell number or eutely, in which the organs and often the entire organism are
composed of a precise and relatively small number of cells. The number may be constant not
only for a species, but also for larger taxonomic groups. The nematode Ascaris, for example,
as well as other closely related genera have a nervous system consisting of precisely 162 cells.
In today's laboratory, we will examine the functional morphology and biology of some
representative nematodes and rotifers and also try to locate them in their natural habitat.
Nematodes are an extremely ubiquitous group of organisms which are found in almost
every conceivable habitat. They outnumber all other groups of species except for the insects
which they probably surpass in total biomass. The majority of nematodes are less than 2.5 mm
in length and are often microscopic. In the laboratory we will examine Ascaris, which is an
intestinal parasite of domesticated animals and humans. Ascaris is large and nicely illustrates
nematode body structure, which is very uniform among species. Since Ascaris is a parasite of
humans, care must be taken in handling it in the laboratory. Even when fixed in formalin, the
eggs of a female Ascaris may remain viable for a number of years.
Nematodes are generally cylindrical and tapered at both ends and when alive, move
actively and continuously. Obtain a preserved male and female Ascaris and examine the
external appearance (p. 119, S&S). Note that the body is covered by a thin, transparent
acellular layer. This is the cuticle, which is secreted by a syncytial layer of cells that underlies
it called the hypodermic. The body is unsegmented, although in some nematodes the cuticle
may be ridged. The sexes are separate in all nematodes, and there is generally a sexual
dimorphism in size, with females larger than males. Can you suggest a reason for this sexual
dimorphism, Ascaris males are easily recognized by their small size and curved posterior end
with copulatory spicules. Can you determine a difference between the dorsal and ventral
surfaces of the worm? Note the lateral line.
Pin an Ascaris specimen, dorsal side up, on a wax-bottom dissecting pan. Cover the
worm with a thin layer of water or continually moisten the internal organs once you cut it open.
Make a straight dorsal cut in the worm extending from the anterior to posterior end and pin the
detached cuticle to the pan. (Be careful not to damage the internal organs when making your
First, examine the digestive system (refer to p. 122, S&S). Carefully tease loose the
reproductive system to expose the intestine. Trace out the alimentary canal: mouth, esophagus,
pharynx, intestine, and anus. Note the relatively straight-tube construction of the gut which is
nonmuscular except for the pharynx. The esophagus is highly glandular. In the living
Ascaris the gut is under high pressure due to the coelomic fluid and the pharynx is responsible
for pumping food against this pressure through the system. Figure 5.8 in S&S p. 127 diagrams
the operation of the nematode pharynx.
The muscular system consists of large, elongate contractile cells with longitudinal fibers
which form specialized units on the dorsal and ventral body walls. Projections from these cells
enter the nerve cords enclosed in the lateral lines. Locate some of these muscle cells under the
cuticle and remove several and examine them microscopically. Careful dissection around the
pharynx may reveal the nerve ring (circumpharyngeal ganglion) lying at an angle around the gut
about halfway between the head and the end of the pharynx.
The excretory system consists of paired excretory tubes, one passing along each lateral line.
Their function, as in flatworms, appears to be chiefly osmoregulation. The excretory tubules
connect to a specialized pair of extremely large excretory cells in the pharyngeal region.
Collected fluids drain out a nearby excretory pore. The pore may not be visible in your
dissection, but you should be able to locate the excretory tubes and possibly the excretory cells as
Examine the arrangement of the internal organs in a prepared cross section under the
microscope. Identify the structures shown on p. 119 of S&S. Do the organs lie free in the
Nemotodes, like other aschelminthes, are covered by a nonliving, acellular protective
covering called a cuticle. The cuticle of nematodes is a complex four-layered structure (see p.
125, S&S). The main component is inelastic collagen which gives the cuticle the properties of
impermeability and rigid strength. For movement to occur, however, the cuticle must be
elastic, and the collagen is laid down as a spiral latticework of parallelograms with protein in
between. Movement of the cuticle results ln a change in the angle between the fibers of the
lattice. Peel a piece of cuticle from your dissected Ascaris. Make a wet mount and examine
it under the microscope. Can you see the plates and layers? Since cuticles form relatively
rigid exoskeleton, they must be periodically shed (molted) to allow for growth.
Nematodes do not have a circular muscle layer. Movement is brought about by
contraction of longitudinal muscles only which are opposed by pressure within the pseudocoel.
In life the pseudocoel is filled with fluid under pressure. A small puncture in the body of a
living Ascaris will produce a sharp jet of pseudocoelomic fluid, demonstrating the high internal
turgor pressure under which the fluid is held. The fluid-filled muscular tube thus forms a highly
developed hydrostatic skeleton, which maintains body shape and is necessary for locomotion.
Unlike ordinary striated muscles, which act between two points of attachment, the muscles of
Ascaris contract in groups, called fields, which produce local shortening of the body wall.
Because the volume on internal fluid is constant and incompressible, the internal pressure in the
pseudocoel is increased, which causes extension of the muscle cells in other regions of the body.
Through this system the dorsal and ventral muscles act as antagonists, producing sinusoidal
waves along the length of the body, propelling the organism (see p. 125, Fig. 5.7, S&S). For
this method of locomotion to work the external medium must be rather viscous (especially for
larger nematodes such as Ascaris). Examine the locomotion of Rhabditis and Turbatrix in
different mediums. Try distilled water, seawater, and seawater thickened with 5X methyl
cellulose. Does the pattern of body movements change? Does the locomotion rate or direction
change? Can you quantify any differences?
Now return to your dissected Ascaris to examine the reproductive system. Nematodes
are dioecious (sexes are separate), and you should be sure to get a good look at both male and
The male reproductive system is a single, long, highly differentiated tube. The thin
terminal portion (blind sac) is the testis where sperm are produced. Sperm move from the testis
into a sperm duct (vas deferens) which enlarges to form the larger seminal vesicle. During
copulation, sperm stored in the seminal vesicle are discharged via the ejaculatory duct out the
cloaca (combined excretory reproductive opening. A pair of spicules that protrude from the
male pore functionally opens the female aperture during copulation. Try to locate sperm cells in
the seminal vesicle. The sperm of nematodes are not flagellated, but move by amoeboid action.
Amoeboid sperm are thought to represent a special adaptation of nematodes. What is the
functional significance of nematode amoeboid sperm?
The female reproductive system of Ascaris is far larger than that of males. Notice,
however, that the basic organization of the two systems is essentially the same: a greatly
modified continuous tube arrangement. Trace the female system from its external opening, the
genital pore, to the vagina, a short heavy tube formed by the fusion of the two large uteri. Each
uterus connects to an oviduct, each of which ends in a greatly elongated, fine tube, the ovary.
The ovaries form a mass of coils about the rest of the reproductive system and intestine, to form a
large proportion or the worm’s interior bulk. It may be diffcult to visualize the entire system as
simply two long tubes joined at the vagina. Tease one tube out to try to demonstrate this.
Eggs formed in the end of each ovary are forced by pressure from masses of younger eggs
behind them to move down the reproductive tube into oviducts and uteri. Near the point where
the oviduct bends back on itself, and enlarges to form the egg-storing uterus, there is a swollen
portion, the seminal receptacle. During a female's lifetime, millions of eggs form and start their
migration down the tube, passing through the seminal receptacle. There they are fertilized by
sperm stored from a previous copulation. The fertilized eggs ehen undergo meiotic division and
the male and female pronuclei fuse. The newly fertilized eggs are then coated to form mature,
heavy-shelled eggs that fill the uteri and are periodically forced through the vagina and out the
genital pore. These eggs become enmeshed in the intestinal contents of the host and are passed
in feces to the soil where development continues. Within the highly resistant eggshells, the
larvae develop, grow, and mole to form the next larval stage. Strictly speaking, the egg is now
no longer an egg, but an encased infective larva. Infection of the vertebrate host occurs after
One species of Rhabditis, Rhabditis maupasi, is a common inhabitant of the excretory
system or coelom of the earthworm. Juvenile worms in the soil are ingested by earthworms and
encyst in the tissues of earthworms. They do not appear to have an adverse effect on living
earthworms. Once the earthworm dies, however, the Rhabditis larvae feed upon the
decomposing tissue and produce young which are ingested by other earthworms and the cycle
continues. We will attempt to demonstrate the presence of Rhabditis in local earthworms from
the Canal Street Bait Shop by culturing decomposing fragments of earthworms.
Obtain a sterile petri dish containing agar which was prepared before class. Transfer a
small fragment (<2 cm) of earthworm tissue to the agar and label the dish. We will let the
dishes stand at room temperature for a week and examine them during next week's laboratory.
You may want to make this experiment more interesting by innoculating different plates with
different types of earthworm tissue, i.e. body wall, intestinal, reproductive, etc.. It would not
be a surprising result to find different nematode species and densities in different host tissues.
To perform this experiment properly you should organize into groups and have each person in
the group test a different tissue. Be sure you control your experiment properly.
Using the agar plate technique we can also examine soil samples for the presence of
nematodes. As with the earthworm agar plates, there will only be one plate available per
student, so you will want to break into groups to test different soil types and depths for
nematodes. To assay soil for nematodes, small bits of soil placed on an agar medium should
yield nematodes (if present) within a week at room temperature. Organize into groups so that
you can compare different soil habitats and, again, don't forget to think about controlling your
Rotifers are microscopic and the majority are found in fresh water. Some rotifers are
characteristic of extremely transient freshwater habitats such as temporary puddles or mosses
which hold rain water. The body of rotifers is cylindrical in cross section, and, like that of
nematodes, is covered by a cuticle. Unlike nematodes, however, the cuticle may be divided into
sections so that telescoping of the body is possible. This cuticular segmentation is not reflected
by the internal organs and is referred to as pseudosegmentation. The anterior end of the body is
in the form of a crown of cilia called a corona which serves as a food gathering device and
functions in swimming. The posterior end of the body may be in the form of a stalk and tapers
into a foot supplied with cement glands in sessile species, or may be relatively unmodified in
Examine the structure and movements of the live rotifers available in the laboratory
referring to p. 120 in S&S to identify structures. Note that rotifers do not have distinct muscle
layer, but possess muscle fiber bundles which traverse the pseudocoel and attach to the cuticle.
The feeding machinery of rotifers is unique. The anterior end of rotifers bears a flat,
ciliated surface called a corona. The coronal cilia create a current of water which draws food
particles toward the ventroanteriorly- positioned mouth. The mouth leads into a highly
muscularized pharynx (mastax) which bears cuticularizec Jaws called trophi. Fluscles in the
pharynx cause the jaws to produce a grinding and chewing action. Salivary glands open into the
pharyngeal cavity and begin the digestive process. Posterior to the pharynx are the narrow
esophagus and sac-like stomach. Paired gastric glands open into the stomach and secrete
digestive enzymes. Cilia line the digestive tract and move food through the digestive system
which terminates in an anus. The digestive system of nematodes lacks cilia. Can you suggest a
reason for this difference between nematodes and rotifers?
Observe living rotifers feeding on a drop of Congo-red-stained yeast. Describe the
pattern of water movement created by the corona and the fate of the food. Can you detect a pH
change in the digestion process?
Rotifers have flame bulbs, similar to those found in flatworms for osmoreregulation.
They are generally found as a pair lying on either side of the mastax. You may be able to see the
flame bulbs if you are patient and slow down the wheel animicules with a drop of methyl
Rotifers have unusual sexual habits. The female reproductive system of rotifers consists
of a single ovary and a yolk-producing vitellarium (see p. 120, S&S). The eggs pass from the
oviduct into the cloaca and then to the outside. Male rotifers are extremely rare and unknown in
some species. They are much smaller than females, lack a digestive system, and have a single
testis which discharges into the cloaca which terminates in an armored penis. During
copulation, the penis is inserted into the female oviduct by puncturing the cuticle.
A generalized life cycle of rotifers is given in the figure at the end of this handout. There
are two types of rotifer females, amictic and mictic. Amictic female always reproduce
parthenogenetically producing eggs that all develop into females, whereas mictic females may
reproduce sexually. Mictic females produce dwarf males as well as resting eggs. The cycle
begins with parthogenetic reproduction which builds the populations rapidly, and then is
terminated by a short period of sexual reproduction stimulated by adverse physiological
conditions. Mictic zygotes are capable of resisting considerable thermal and desiccation stress.
This pattern is variable, however, and some rotifer species appear to only reproduce
parthenogenetically. Males are not known in these species.
Because rotifer life cycles contain a resting (mictic) egg stage able to withstand drastic
conditions, they are often the numerically dominant animal in temporary aquatic habitats such as
puddles. When these habitats are dry, the mictic zygotes are present and mature to amictic
female rotifers under an appropriate stimulus. This change can happen within an hour and is
generally in response to moisture and/or food. Today we will try to find rotifers in dried puddles
if it hasn't rained lately, or we will try to find them in an active state in puddles.
Try to think of an ideal location nearby where temporary bodies of water are common.
Flat rooftops generally work well on the west coast. If you know a good location, go there and
procure a small amount of sediment or detritus in a 250 ml beaker. On returning to the
laboratory, divide the sediment equally between two 250 ml beakers. Add approximately 100
ml of distilled water to the beakers, and seed one of the cultures with a couple drops of
Chlamydomonas culture and a dash of yeast. Start this experiment at the beginning of the
laboratory period and examine drops of the culture under the compound microscope at the end of
the laboratory. Whether or not you find anything at the end of the lab period, label your beakers
clearly and we will incubate them at room temperature for a week and examine them during next
ROTIFER LIFE CYCLE:
LABORATORY 6: PHYLUM ANNELIDA
The annelids or segmented worms are characterized by an elongated body, divided into
segments and formed on the plan of a tubular jacket of muscle surrounding a fluid-filled coelom.
Although lacking a rigid internal skeleton. annelids can use the hydrostatic pressure of coelomic
fruit, acted upon by the muscular body wall, as a "fluid skeleton," aiding in extension and flexing
of the body in crawling, swimming, and burrowing. Locomotion in some annelids is also aided
by numerous fine chitinous hairs, called setae, which project from the sides of the body. The
annelid body plan has proven to be extremely plastic and adaptable in an evolutionary sense, so
that we find a great diversity of form, habitat, and life style within the phylum.
Three annelid classes are generally recognized: 1) POLYCHAETA have many setae
(hence the name) and lateral body wall lobes called parapodia, as well as a diversity of tentacles
and gill-like devices. Polychaetes are almost entirely marine, exceedingly diverse in form, and
very numerous, comprising about 60 families and some 1600 genera. Archiannelida, a small
and poorly known marine group, may be regarded as an order or subclass of Polychaeta rather
than as a distinct class. Archiannelida are small worms that show a curious assortment of
features, including weak segmentation, poorly developed parapodia, and frequent lack of setae.
Some of these features may be primitive, others reduced. 2) OLIGOCHAETA have no
parapodia and few setae (as the name implies). They include the familiar earthworms, as well as
many marine and freshwater representatives. 3) HIRUDINEA or leeches have no setae or
parapodia and are found mainly in fresh water.
Annelids are typically bilaterally symmetrical, elongate in an anterio-posterior- direction,
cylindrical in cross section, and divided externally by a series of rings into body segments
(metameres). The external segmentation is reflected by the arrangement of the internal organs,
which are serially repeated. This condition is known as metamerism and is particularly
pronounced in primitive polychaetes. Metameric segmentation distinguishes the annelids from
other worm-like forms. It provides a degree of plasticity in that certain segments can become
modified and specialized to carry out specific functions, and segments can respond either
individually or collectively.
The annelid gut is a straight tube supplied with its own musculature, so that it functions
independently of muscular activity in the body wall. Like nematodes, annelids have a
fluid-filled internal cavity which separates the gut from the body wall and is similarly involved in
locomotion as a hydrostatic skeleton. However, this space is not embryonically derived from the
blastocoel as with nematodes, but is formed much later in development as a split in the
mesoderm by which it is entirely lined (schizocoely). This fluid-filled internal space is a true
coelom as found in arthropods and chordates.
The excretory and circulatory systems are well developed, and some members of the
phylum have respiratory organs (gills). The nervous system is concentrated anteriorly
(cephalization) into cerebral ganglia from which arises a ventral nerve cord with segmental
ganglia. The nervous system coordinates activity among segments
In today's laboratory, we will examine the functional morphology of representative
annelids from each of the three classes:
Examine the external features of the oligochaete available in the laboratory. This will
probably be the common earthworm Lumbricus, which lives in moist soil, remaining in its
burrow during the day but emerges from its burrow during the evening or after it rains. Note the
well-marked external segmentation. Locate the nonannulated segment (the clitellum) which
functions as an attachment point turing copulation and in the formation of egg cases or cocoons
(see p. 139, S&S). Observe the subterminal mouth. The preoral area is called the
prostomium (pro, before; stoma, mouth; GK). The first true segment of the body surrounds the
mout and is called the peristomium (peri, around; stoma, mouth; GK). Locate the anus at the
posterior end of the body. Note the presence of bristles (setae) on the body of Lumbricus.
Describe the distribution and orients of the setae. Are they evenly distributed on the dorsal and
ventral surfaces? they directed anteriorly or posteriorly?
Prepare a Lumbricus specimen for dissection by placing it in freshwater, dissolving a
small amount of magnesium chloride in the water, and then adding ethyl alcohol to bring the
solution to approximately 30% alcohol. When the worm has succumbed, remove it from the
solution and place it on a wax-bottomed dissect pan, keeping it moist throughout your dissection.
The entire surface of Lumbricus is covered by a cuticle. Strip the cuticle from segments 9-15
and, using the dissecting scope attempt to locate the external genital openings. Oligochaetes are
hermaphrodites (monoecious). The paired vase deferentia open lateroventrally on the fifteenth
segment, and seminal grooves lead back from them to the anterior edge of the clitellum. During
copulation, sperm pass along the grooves to the spermathecae of the partner worm. The
spermathecal openings are located between segments 9 and 10 and 10 and 11 at the same level as
the dorsal setae. The oviducts open on segment 14. Attempt to locate the nephridial openings
on one or two of the stripped segments. These openings are dorsal to and in front of the ventral
row of setae in all segments except the first three and the last. What is their function?
Middorsal coelomic pores open from the coelom in the segmented groovee of all segments
following 10, but are difficult to see. In life they exude coelomic fluid and help to keep the
Now examine the internal structure of Lumbricus. Anchor your specimen to the pan by
means of a pin through the prostomium, and make a dorsal longitudinal incision with a pair of
scissors (see S&S, p. 148). Be careful not to injure the internal organs when making the
incision. Using forceps and a dissecting needle, open the cut and free the body wall from the
septa. Note how the septa are segmentally arranged and how the gut is held in place by septa.
Once your worm is opened, pin the body wall to the pan to fully expose the internal structures.
Using the diagram on p. 148 of S&S, identify the internal structures. The muscular pharynx is
the principal organ of digestion; it narrows posteriorly to form the esophagus, which is
surrounded by the five pseudohearts of the closed circulatory system. Can you detect the
cerebral ganglia and longitudinal nerve cords? In segment 10 is a pair of small diverticula, the
esophageal glands which secrete digestive enzymes. In segments 11 and 12, similar pairs of
esophageal glands contain calcium carbonate particles and have a whiteish color. These
calciferous glands are excretory in function and appear to function in controlling the level of
calcium ions and pH in the blood and coelomic fluid. Posterior to the esophagus is a thin-walled
crop (segments 14-16) which temporarily stores food as it is being digested and the thick-walled
gizzard (segments 17-19) which physically masticates the food. The remainder of the gut is the
stomach-intestine where the products of extracellular digestion are absorbed. This area is
covered by yellowish chloragogue cells where glycogen synthesis, protein deamination, and the
formation of ammonia and urea occur.
Oligochaetes such as Lumbricus have a fairly well-developed blood vascular system with
main pulsating contractile vessels, and capillary networks supplying the gut, body wall, and other
organs. Locate the dorsal and ventral blood vessels of Lumbricus and the pseudohearts. Blood
is moved anteriorly in the contractile dorsal vessel and posteriorly in the ventral vessel. The red
color of the blood is due to the presence of haemoglobin which is not carried in cells, but is free
in the blood and coelomic fluid.
The excretory organ found in most annelids is the nephridium. In Lumbricus, almost
every segment contains a pair of nephridia. Each consists of a ciliated funnel, the nephrostome,
which communicates with the coelomic cavity and is situated posteriorly in the segment. A duct
leads from the nephrostome, passes through the intersegmental septum posterior to the
nephrostome, and continues as a fine ciliated coiled tubule surrounded by blood capillaries. The
tubule leads to a bladder that discharges to the exterior via a nephridiopore, which opens near the
ventral pair of setae. The cilia of the funnel and tubule beat and draw fluid from the coelom;
wastes and other materials are exchanged with the blood in the capillaries surrounding the tubule.
By filtration, reabsorption, and tubular secretion, the nephridia perform their excretory function
and maintain salt and water balance. If time permits, examine a nephridia of Lumbricus under
the compound scope. If you are lucky, you will be able to see the ciliary currents moving fluid
through the system. See p. 158 of S&S for a diagram of a Lumbricus nephridium.
Before leaving your dissection of Lumbricus, remove the gut to examine the reproductive
structures. Refer to p. 148 of S&S. Segments 9-13 carry the trilobed seminal vesicles where
sperm develop. Observation of this tissue under the compound scope should reveal developing
sperm. Sperm are produced in the small paired testes located in segments 10 and 11. Sperm
exits the male system via vas deferens which open to the outside in segment 15. The female
reproductive orgas will initially be obscured by the seminal vesicles. Below them, in segment
13 you should be able to find two small ovaries attached to the anterior septum. The ovarian
funnel projects forward from the posterior septum of segment 13 and leads to a short oviduct in
segment 14 which leads to the female genital pore. Segments 9 and 10 contain yellow sperm
receptacles (spermathecae), which store sperm from another worm.
Examine a prepared cross section of Lumbricus and identify the structures shown on p.
139 of S&S. Pay particular attention to the musculature.
To examine the locomotion of Lumbricus, obtain a live worm and place it on a sheet of
moist paper toweling that has been ruled with lines approximately 1 cm apart. Allow the worm
to crawl across the sheet and carefully note how the worm moves forward as a wave of peristalsis
passes along its body. Does the wave pass from anterior to posterior or vice versa? Do the
expanded and contracted regions of the body move forward during a wave of peristalsis? Now
place the worm on a smooth surface such as a wet glass plate. Does the animal move? Why?
Knowing that the coelom and musculature of each segment of Lumbricus is isolated from the
coelom of adjacent segments, what is the role of circular muscles, longitudinal muscles, coelomic
fluid, setae, and the nerve cords in the locomotion of Lumbricus.
Examine the external characteristics of Nereis or any other errant polychaete available in
the laboratory. Refer to pages 140-141 to identify structures. The most obvious difference
between Nereis and Lumbricus is the presence of lateral segmental projections in Nereis. These
parapodia are used in swimming and crawling movements. Closely examine the parapodium
of a Nereis you have anesthetized by placing in a dilute solution of Magnesium chloride and then
rinsed. Each parapodium is biramous, consisting of a bilobed dorsal notopodium and a ventral
neuropodium, which functions in both respiration and locomotion. From each there arises a
tactic cirrus and a bundle of jointed chitinous setae. They are fine bristles composed of a long
blade jointed to a sturdy shaft. The setae arise from invaginated sacs in the parapodia, and each
one is secreted by a single cell at the base of each sac. The parapodia are supported internally by
two modified setse called acicula. Examine the number and arrangement of the setae. How do
they differ from Lumbricus?
The anterior end of Nereis shows conspicuous cephalization and differs distinctly from
that of Lumbricus in that it bears a pair of prostomial tentacles, paired palps and eyes. The
peristomium is also more elaborate in having tentacular cirri. The peristomium is thought to be
composed of two fused segments and the peristomial cirri are the modified cirri of normal
segments. The mouth is equipped with an eversible pharynx armed with serrated teeth. The
pharynx is everted during feeding in predaceous polychaetes such as Nereis.
Examine a prepared cross section of Nereis and identify the structures illustrated on p.
140 of S&S. The entire surface of the parapodium and the body proper is covered by a thin
cuticle secreted by a single layer of cells that underlies it, the epidermis. Below the epidermis
are a layer of circular muscles and four bands of longitudinal muscles (dorsal and ventral pairs).
Oblique muscles originate on the median ventral surface and pass to the body wall. This
arrangement of musculature acting on the incompressible coelomic fluid, permits the body to be
shortened by contraction of the longitudinal muscles and lengthened by contraction of the
circular and oblique muscles. The musculature of the various polychaete types differs
considerably and will be discussed below.
At least one person in each laboratory section should dissect a Nereis to examine internal
structure and share the results with the rest of the class. The dissection should be carried out as
described for Lumbricus. Before dissection, the Nereis should be treated with magnesium
chloride in salt water and then the saltwater should be diluted with ETOH to 30% alcohol.
Identify the structures illustrated on p. 141 in S&S.
Locomotion in Nereis can be examined in the same manner that we looked at Lumbricus
locomotion. Place a small living Nereis on a piece of wet paper towel ruled with lines 1 cm
apart and observe the progression of the worm. Are its movements like those of Lumbricus?
Describe the movement pattern of Nereis. Record the flexures of the body and successive
positions of the parapodia. Do parapodia on opposite sides of the body move synchronously in
the same direction? Do all parapodia on one side of the body move synchronously? Describe
the motion of a single parapodia. How are the movements of the parapodia related to the
twisting of the body? What enables the parapodium to remain stiff during an effective stroke?
How is surface friction achieved? Try watching Nereis move on a glass plate. What is the
result? Does the undulatory wave pass along Nereis in the same direction as the wave of
contraction during movement in Lumbricus? Given that the longitudinal muscles of Nereis are
primarily responsible for locomotion and the role of the coelomic fluid and circular muscles is
not as great as in Lumbricus, construct a mechanism for the movement pattern of Nereis
(remember the arrangement of muscles you saw in the cross section).
Some polychaetes are active swimmers. While this is not the usual habit of Nereis, it
will show you how it is accomplished. Place a Nereis in a dish of saltwater and observe the
swimming motion by picking it up from the bottom and letting it swim away. In what way does
the swimming motion differ from the crawling motion?
Below, I have provided a summary of life style types among polychaetes. Read Barnes
for more details. Examine living representatives of as many of these types as we have available
in the laboratory for study.
1. Crawling polychaetes - The crawling polychaetes are basically surface dwellers, living in
rock and coral crevices or beneath rocks and shells. In these worms the prostomium is equipped
with eyes and other sensory organs, the parapodia are well developed, and the body segments are
generally similar. Nereis is a good example of this type of polychaete.
In crawling species, the longitudinal muscle layer is better developed than the circular
layer, which may even be absent, and the septa tend to be incomplete. Movement is brought
about by the combined action of the parapodia, the body wall musculature, and to some extent
the coelomic fluid. The pattern of locomotion in Nereis is typical of many crawling polychaetes.
The slow crawling movement of Nereis results entirely from the action of parapodia. Parapodial
movement involves a backward effective stroke in which the parapodia are in contact with the
substratum and a forward recovery stroke in which the parapodia are lifted from the ground.
Each parapodium describes an ellipse as it completes one of these two-stroke cycles. The
acicula and setae of the parapodia are extended during the effective stroke and retracted for the
forward recovery stroke.
The combined effective sweeps of the numerous parapodia propel the worm forward.
The right and left parapodia of each segment work alternately rather than simultaneously. In
other words, when a particular group of parapodia on one side of the body is executing an
effective stroke, the parapodia on the opposite side are executing the recovery stroke. The
parapodial action takes place in waves along the side of the worm, with every fourth to eight
parapodium (depending on the organism) being in the same phase of the cycle. The waves of
activation of the parapodia move from posterior to anterior.
In some crawling polychaetes, S-shaped body undulations, in addition to parapodial
action, are responsible for locomotion. Body undulations are produced by waves of contraction
in the longitudinal muscles of the body wall. These waves of contraction coincide with the
alternating waves of parapodial activity just described. The longitudinal muscles on one side of
each segment contract when the parapodium on that side of the segment is moved forward; the
muscles then relax as the parapodium sweeps backward in its effective stroke. The principal
force of propulsion in this type of movement comes not from parapodial movement, but rather
from body contractions pulling against points of contact made by the parapodia.
2. Pelagic polychaetes - Six families of polychaetes contain exclusively planktonic or pelagic
species. They are morphologically similar to crawling forms, except that most of them tend to
be transparent and many of them lack setae. (Why to you suppose this is so?) The swimming
movements of these polychaetes are S-shaped undulations similar to those described in the
preceding paragraph. We have no polychaetes of this type in the lab.
3. Burrowing polychaetes - Many polychaetes, such as Glycera, have become adapted for
burrowing. Most of them construct a system of mucus-lined galeries within which they move
about. The adaptations of many of these burrowers remarkably parallel those of the earthworms
of the class Oligochaeta. The prostomium is reduced and pointed; eyes, palps and antennae are
usually absent; parapodia tend to be smaller than those of crawling surface dwellers. Burrowing
polychaetes move through the substratum by means of peristaltic contractions. The circular
muscle layer of the body is well developed and the septa effectively compartment the coelomic
fluid and localize its function as a hydrostatic skeleton.
Many polychaetes occupy more or less fixed simple burrows excavated in the
substratum and are referred to as sedentary burrowers. Movement through the burrows results
from peristaltic contractions. Thus the parapodia are greatly reduced and are in part
represented by transverse ridges provided with setae modified into hooks. The prostomial
sensory appendages are generally absent in this type of worm, but the head may carry specialized
feeding structures. Amphitrite is a good representative of the sedentary burrowers.
4. Tube-dwelling polychaetes - A tube-dwelling habit has evolved in many families of
polychaetes. The tube may serve the worm as a protective retreat or as a lair for catching
passing prey. It may provide access to clean oxygenated water above a muddy or sandy bottom
or may permit a worm to inhabit hard, bare surfaces such as rock, shell or coral.
One group of tube-dwelling polychaetes contains worms which are typically carnivorous
and extend from the opening of the tube to seize passing prey. They are not greatly different
from the surface-dwelling polychaetes in terms of morphology. Prostomial sensory appendages
are well developed and the parapodia, which are used in crawling through the tube, are not
markedly reduced. Diopatra is an intertidal worm representative of the carnivorous
tube-dwellers. Diopatra build heavy, membranous tubes from secretions of special glands
located on the ventral surface of the segments. The chimneys of the tubes, which project above
the sand or mud sediment, bend and flare at the end like a funnel. These chimneys are covered
with bits of shell, seaweed and other debris that the worm collects and places ln position with its
Another interesting tube dweller is Pectinaria. This worm constructs a tube by
cementing together sand grains. The tube is conical, with the smaller end of the tube opening at
the surface of the sand or mud sediment. The head of the worm bears rows of large conspicuous
setae that are used in digging. Pectinaria never comes completely out of its tube, but it can
move around in the environment carrying the tube with it.
Most tube-dwelling polychaetes, however, are highly modified for a sedentary
tube-dwelling existence and exhibit characteristics similar to the more sedentary burrowers.
Prostomial sensory appendages are reduced or absent, while special anterior feeding structures
are often present. The worms usually move within the tube by peristaltic contractions, and the
parapodia are reduced and provided with hook-like setae. The body segments are commonly
differentiated into regions. Sabella and Hydroides are good examples of sedentary
Sabella and Hydroides belong to a group of polychaetes commonly referred to as feather
duster worms or fan worms. In these worms the prostomium has developed to form a spiral or
funnel-shaped crown consisting of a variable number of pinnate processes called radioles.
When the radioles are extended they look like a feather duster, hence the name. The radioles are
rolled up or closed together whe the worm withdraws its anterior end into the tube.
Sabella constructs a tube of sand grains imbedded in mucus. The worm sorts detritus
collected by the ciliated radioles, and sand grains of suitable size for tube construction are stored
in two sacs below the mouth. The walls of these sacs produce mucus, which is mixed with the
sand particles. A rope-like string of mucus and sand grains is then released when the worm
makes additions onto the end of the tube.
Hydroides secretes a calcareous tube which is attached to rocks or shells. Two large
calcium carbonate secreting glands are located on the prostomium. The dorsal radiole of this fan
worm is modified into a long stalked knob called an operculum which acts as a protective plug
at the end of the tube when the crown is withdrawn. If Hydroides is available in the lab, be sure
to see the quick retraction response it has to disturbance. This rapid response is possible
because of a giant fiber nerve system and well developed longitudinal muscles.
Examine the external anatomy of the live leeches available in the laboratory (probably
Hirudo). Refer to pg. 142 of S&S. Can you locate any setae? In what plane is the body
flattened? All leeches have a constant number of segments (34), but secondary external
annulation obscures the true segmentation which is apparent in the arrangement of the internal
structures. How many annuli are there per segment in Hirudo? One annulus of each segment is
marked by a row of sensory papillae. Five pairs of dorsal papillae in the first five segments are
modified into eyes. The more pointed anterior end of the leech bears a small ventral sucke
formed from the prostomium and peristomium. The posterior end bears a large ventral sucker
made up of segments 25-34. The single opening of the vas deferens is located midventrally at
the second annulus of segment 10. The penis issues from this pore. The vagina opens
midventrally at the second annulus of segment 11. Like the oligochaetes, leeches are
hermaphroditic and cross copulation is the rule. Nephridiopores open lateroventrally at the last
annulus of each segment from 6 to 22, but are difficult to see. The clitellum develops seasonally
on segments 9-11 which bear abundant secretory cells.
Examine a prepared slide of a cross section of a leech. Refer to p. 142 of S&S. The
surface arrangement of the musculature in the leech is similar to the other annelids with an outer
circular layer of muscles and an inner longitudinal layer. Leeches, however, also have
dorsoventral muscles which maintain the compressed shape and aid in locomotion. The
coelomic space is reduced by mesenchymal tissue. This tissue consists of fine capillaries of the
coelomic blood sinus system surrounded by globular cells forming a connected system of
sinuses. The sinus system is continuous between segments and septa are reduced or absent.
The gut is provided with branches called caeca, which increase the surface area for digestion.
The reduction of the coelom and lack of a discrete segmental hydrostati skeleton is reflected in
the method of leech locomotion.
Locomotion in leeches is drastically different from other annelids. Septa are absent, and
the entire body functions as a unit. The coelomic cavity is reduced so does not have as
important a role as a hydrostatic skeleton. Movement in leeches is caused primarily by opposing
contractions of the circular and longitudinal muscles. The oblique muscles run as a helical
spiral along the length of the body. When the body is long and thin the spiral fibers reinforce the
longitudinal muscles; when the body is short andthick, they reinforce the circular muscles that
produce elongation. When the spiral muscles are neither lengthened or shortened, they maintain
internal pressure and enable the leech to lift its anterior or posterior end off the substrate.
Leeches can swim and creep. Take a living leech, drop it into a container of freshwater,
and observe the swimming motion. In what plane are the undulations? In what direction does
the undulatory wave pass? Contrast the swimming movement of leeches with that of Nereis.
How do you think the musculature of leeches causes the swimming movement?
To study the creeping movement of leeches, place a leech in a watch glass over a piece of
lined paper and watch its movements. Record the sequence of movements and the action of the
suckers over time. After you have determined the behavioral sequence of leech crawling,
perform the following experiment. Place a leech in a watchglass of freshwater and allow the
posterior sucker to attach to a coverslip held above the bottom with forceps. What is the
response? Release the coverslip. What happens? Now present a second coverslip to the
anterior sucker and allow the leech to attach as the coverslip is held above the bottom of the dish.
Does the posterior sucker remain attached? Release the coverslip. What happens? Explain
these observations. What movements occur if the anterior end of the worm ls supported by a
piece of string and the sucker makes no contact? What body movements occur if both sucker
areas are supported by loops of string?
Prepare your leech for dissection by placing it in freshwater, allow it to relax and then add
some magnesium chloride. When it is completely expanded add enough EtOH to bring the
solution to 30%. Pin the specimen to a dissecting pan and make a dorsal incision as you did
with Lumbricus. Carefully separate the skin from the body and pin it down. Examine the
internal structures under a dissecting scope. Try to locate the structures illustrated on page 142
of S&S. This is not easy due to the large amount of mesenchymal tissue and the oblique
muscles. These tissues can be carefully removed to see internal structure. In any case, note the
mesenchymal tissue, oblique muscles, and the lack of a large coelom and segmental septa. How
does this compare to the internal anatomy of Lumbricus and Nereis?
COMPARISON OF ANNELID CLASSES
Polychaeta Oligochaeta Hirudinea
Representative: Nereis amphitrite Lumbricus leech
1. Cephalization often elaborate sensory reduced reduced
or feeding structures
2. Parapodia and/ parapodia often well- no parapodia; a few no parapodia
or setae developed with many setae no setae
3. Sexuality usually separate sexes hermaphroditic
4. Reproductive many small eggs few large eggs few large eggs
5. Fertilization external within a cocoon internal
6. Development external within a cocoon within a
7. Hatching Stage free-swimming small adult small adult
8. Habitat chiefly marine fresh water or moist fresh water or
soil moist soil
9. Feeding mode Diverse: predators, direct deposit feeders predators or
filter-feeders, direct or blood-sucking
indirect deposit feeders, ectoparasites
LABORATORY 7: PHYLUM MOLLUSCA
The phylum mollusca is one of the largest of all phyla, both in the size of certain species
and the number of species which have been described. There are approximately 90,000
described species. Early molluscs were abundant in cambrian seas and the long history of the
group is reflected today in the variation among molluscan types. This variation also attests to
the success and plasticity of the basic molluscan body plan, which is far from obvious in some
modern members of the phylum.
The basic molluscan body plan is bilaterally symmetrical, unsegmented, protostomate, and
coelomate and the body is divided into a ventral muscular foot, a dorsal visceral mass, and a
mantle (pallium) of epithelium and other tissue which encloses the dorsal surface of the body.
The cavity between the mantle and visceral mass is termed the mantle cavity. The visceral
mass is provided with a blood circulatory system generally containing the oxygen carrying
copper pigment haemocyanin, a variably specialized and cephalized nervous system with ganglia
and ventral nerve cords, a well developed excretory system, and a distinct reproductive system.
The mantle cavity generally houses an efficient respiratory system. As will be seen in today's
laboratory, however, among the molluscan classes almost every one of the organ systems
mentioned above shows a wide spectrum of variation.
Molluscs apparently arose as creeping types, probably living on hard surfaces and scraping
their food from the substrate by means of a unique organ, the radula, which is found in all
modern classes except the Bivalvia (Pelecypoda). Bivalves have extensively modified their gills
(ctenidia) for filtering particulate food from the water column. The molluscs are closely related
to the annelids. This affinity is seen in the similar developmental patterns within the two
groups, the trochophore larva, and the possible vestiges of segmentation seen in some of the
The molluscs are divided into six classes: Monoplacophora, Polyplacophora (=
Amphineura, chitons), Gastropoda (snails), Pelecypoda (bivalvia, clams), Cephalopoda (squids
and octopus), and Scaphopoda (tooth shells). In today's laboratory we will deal primarily with
gastropods, pelecypods, and cephalopods, the three numerically dominant classes. You will
perform dissections on members of each of these classes to get a handle on their similarities and
differences. We will also examine some aspects of molluscan locomotion and feeding. You
will have to carefully allocate portions of today's work to members of your laboratory group to
The gastropods are more similar to the ancestral molluscan form than any of the other
molluscan classes we will be examining today. They differ from the primitive ancestor in
having an enlarged head and visceral mass, in most cases a logorithmically spiraled shell, and a
visceral mass that has undergone a 180° rotation during development (torsion), so that the gills
and anus are located on the anterior end of the snail. Before proceeding with the dissection of a
marine prosobranch and terrestrial pulmonate snail examine the collection of shells available in
the laboratory. Try to determine the possible advantages and disadvantages of different shell
types. How do the shells of rocky shore, soft bottom marine, terrestrial, and freshwater snails
Examine the external features of a preserved specimen of Busycon, which has been
removed from its shell. In life Busycon is a predator found in soft bottomed littoral habitats
which preys mostly on bivalves. On the foot locate the thin horny operculum, which in life
closes the aperture of the shell and protects the animal that is retracted inside. Near the anterior
end of the sole of the foot is the opening of the pedal gland, which produces mucus which
facilitates movement. The mucus also helps the snail adhere to hard substrate by suction
produced by contraction of the central portion of the foot. The pedal gland is also important in
forming egg cases which are attached by females to hard substrate. The triangular mouth is
located at the end of the proboscis which extends from beneath the paired tentacles. Note the
eyespots on the tentacles. In male specimens, a large penis can be seen by the right tentacle.
The coiled visceral mass is covered by a thin mantle, which thickens to form a collar at the base
of the viscera. The shell is secreted at the edge of the collar. The collar is elongated posteriorly
to form an extensible siphon through which water is drawn into the mantle cavity. What is the
advantage of the siphon?
Through the mantle at the apex, locate the right lobe of the brownish digestive gland or
liver on which lies the yellow or orange gonad and a straight (female) or coiled (male) gonoduct.
See pp 234-235 in S&S. These two organs fill the first and smallest whorl of the shell.
Examine the Busycon shells in the laboratory to get an orientation on how your specimen would
be situated in its shell. The next whorl is occupied by the left liver lobe as well as the stomach
and part of the intestine. The large brown kidney and heart are located along the dorsal surface
to the left of the base of the visceral mass. Anterior to the heart and kidneys lies the oblong
ctenidium and the sensory osphradium and traces of the mucus-secreting hypobranchial gland.
Examine the configuration of the organs of Busycon. How would they be arranged in an
untorted snail? List differences between Busycon and an unsorted snail which have resulted
Examine a Busycon shell and notice that it is composed of several spirally arranged whorls.
The large terminal whorl is called the body whorl. The shell is actually a coiled tube leading
from the body whorl to the apex and wound around a central column or columella. Examine a
sectioned Busycon shell to see the three structural shell layers, the outer periostracum, middle
prismatic layer and inner nacreous layer. Busycon is one of the few gastropod species which
exhibits both right handed (dextral) and left handed (sinistral) coiling. In Busycon this is a
genetically determined trait. Most snails are dextral. You can determine handedness in a snail
by holding it with its apex up and aperture pointed toward you. If the aperture opens to the right
the shell is dextral; if it opens to the left it is sinistral.
Return to your preserved Busycon and open the mantle cavity by making a median incision
about a centimeter to the right of the middorsal line along the ctenidium until you reach the
pericardium. Avoid disturbing the heart. Observe the single attached ctenidium composed of
only one row of filaments. Anteriorly, on the inhalent side of the ctenidium, is a brownish
chemosensory osphradium composed of about 100 triangular filaments covered with epithelium.
The osphradium functions in monitoring the quality of incoming water. Along the cut edge of
the mantle lies the anus at the end of the rectum, and to its left the mucus-secreting
hypobranchial gland formed of heavy folds of the mantle. The mucus secreted by this gland
helps to consolidate particles rejected by the gills before leaving the mantle cavity, preventing
If the proboscis is extended, observe the position of the radula within the mouth at the tip
of the proboscis. Specimens in which the proboscis is not extended should be dissected by
making a cut between the tentacles to expose the proboscis. Slit the proboscis along its length
and examine the esophageal cavity, the radula, and the odontophore (see p. 234, S&S).
Examine the muscles that control the odontophore and the radula. By cutting these muscles,
free the radula and place it into 10% potassium hydroxide for later examination. Next try to
identify the components of the digestive tract illustrated on p. 234 of S&S (Fig. 8.4B).
Be sure you examine the one Busycon specimen in each laboratory which has been injected
with colored latex to show the details of the circulatory system. Try to determine the flow of
blood through Busycon.
Before discarding your pickled Busycon be sure to take note of the esophageal nerve ring.
Also, trace the nerve cords from the nerve ring and verify that they do not form a straight loop as
in primitive molluscs (like chitons), but rather have a figure eight configuration. Why is this so?
Obtain a freshly killed specimen of the pulmonate snail Helix. Helix is a terrestrial
herbivore. Using bone cutters, carefully cut around the spirals of the shell and remove the
animal (See p. 236, Fig. 8.5C, S&S). Leave only the central column (columella) and be
careful not to disturb the soft parts. With the aid of the figures on p. 236 of S&S, identify the
external and obvious internal structures of Helix. What differences do you see between Helix
and Busycon? Pay particular attention to the mantle cavity, the roof of which is richly supplied
with blood vessels. The mantle cavity serves as a functional lung. There are no ctenidia.
Examine a living specimen of Helix under the dissecting microscope and observe the rhythmic
opening and closing of the pneumostome, a small aperture on the right side of the body. This
opening leads to the pulmonate lung.
Returning to your shell-less Helix, sever the columellar muscle and, then by inserting one
blade of a scissors through the pneumostome, cut the mantle from the body wall in both
directions from the pneumostome. Pin your specimen to a wax pan as shown in S&S, p. 236,
Fig. 8.5D and try to identify the internal structures shown. Before leaving your dissection,
locate the buccal mass and cut out the radula and place it in 10% potassium hydroxide.
The radula is the characteristic feeding organ of all molluscan groups except pelycepods.
It is used as a scraper, a rasping tongue and as a drill. Its architecture differs among species
depending on how it is used. Obtain recently killed specimens of Littorina and Urosalpinx,
remove them from their shells and try to dissect out their radulas. Place the radulas in 10%
potassium hydroxide. You should now have the radulas from two herbivorous snails Helix and
Littorina and two carnivorous snails Busycon and Urosalpinx. Boil each of these for 10 minutes
in test tubes containing 10% potassium hydroxide. This will dissolve unwanted tissue and make
the teeth more clearly visible. Examine each of the radulas under the microscope and describe
and compare their structure. Also, examine the prepared slides of the radula of a chiton. How
does the radula of each of these molluscs relate to its feeding habits?
Locomotion in most gastropods is accomplished by muscular contractions of the foot aided
by mucus secretion. Exceptions to this general pattern include swimming gastropods and
gastropods that use cilia to locomote. In gastropods that move by the muscle/mucus method,
there are two specific ways by which movement is achieved: 1) direct muscular waves where
the posterior edge of the foot is lifted, moved forward and then this advancing wave is
propagated forward and 2) retrograde muscular waves where the anterior end of the foot is
stretched and attached and the advancing wave is propagated backwards. These two modes of
locomotion are illustrated in Barnes, p. 341. Attempt to characterize the type of locomotion
mechanism found in Helix, Littorina, and Urosalpinx. To do this have the snail settle on a
plexiglass plate (in an aquarium with Littorina and Urosalpinx) and then tilt the plate so that you
can examine the movement of the foot from beneath. Use a magnifying glass if they are
available. Do all these snails move in the same fashion? Does substrate angle influence
whether a snail moves by direct or retrograde waves? Which of these modes do you think is the
Torsion in gastropods probably evolved to increase the protective valve of a gastropod's
shell by allowing them to retract into their shells head first and cover the aperture with a horny
operculum. Torsion, however, created the sanitation problem of putting the anus directly over
the head. Gastropods have evolved a number of solutions to this problem involving the
direction of water currents in the sorted anterior mantle cavity. To get an idea of how the most
prevalent of these solutions works, place a Littorina or Urosalpinx in a shallow finger bowl filled
with saltwater and allow it to settle. With a pipet gently place a drop of a carmine suspension in
front of the snail and observe the movement of the carmine. Try this also with Crepidula.
What is the major difference between the water currents of Crepidula and the other snail? Why
do you think this is so? Examine the ventral surface of Crepidula and describe how it differs
from the other snails you have examined. Why might Crepidula be described as bivalve-like?
While most prosobranch snails (torted, gill-bearing snails) are dioecious, some are
hermaphroditic. Pulmonate (lung bearing) and opistobranch (detorted, sometimes shell-less)
snails are hermaphroditic. In the aquaria, you will find a number of "stacks" of Crepidula
fornicata individuals, a sequentially hermaphroditic prosobranch snail. Crepidula juveniles start
out life as a males, generally settling on the shells of older conspecifics. Later in life Crepidula
individuals change sex to females. This change, however, is mediated by the presence or
absence of other females. In the presence of other females, males stay males. Male Crepidula
can be discerned by the presence of a penis to the right side of their head. Examine the sexual
composition of one of the Crepidula communes in the aquaria. Do your observations confirm
the above scenario? Of what advantage do you think this tactic is to an individual snail?
Bivalves do not initially appear to have much in common with snails or the primitive
molluscan form except for their protective shell. Bivalves are generally sedentary. The foot,
visceral mass, and mantle cavity dominate the body, and the head is suppressed. Bivalves have
developed from the primitive molluscan form by enlarging the mantle and dividing it into
symmetrical halves hanging down on both sides of the body, enlarging the gills in the now huge
mantle cavity, and extending the foot downward between the mantle folds as a blade-like
structure. Bivalves have lost the radula and the majority are ciliary feeders with large, platelike
food-gathering gills (ctenidia). The extensive mantle encloses the entire body in two
symmetrical flaps which secretes a hinged, two-part shell.
Obtain a specimen of the clam, Mercenaria and examine its external features (see p. 238
of S&S). Note the umbo of the shell and the growth lines. What does the umbo represent?
How do clams grow? Also identify the hinge ligament, the siphons, and muscular foot. What
is the function of each of these structures?
Identify the right and left valves of your Mercenaria. Do this by orienting the anterior
end of the clam up and noting that the umbo is on the dorsal side of the body. Take a sharp
scalpel and carefully insert it between the valves and, moving the blade along the ventral edge
close to the left valve, cut the adductor muscles which effect shell closure. You will probably
need to insert a pair of scissors between the valves to hold them open while cutting (see p. 238 of
S&S). Once you have cut the muscles, remove the left valve to examine internal anatomy.
Underlying the shell is the fleshy mantle. Note how it hangs like a sheet, attached dorsally and
free ventrally. The dorsally located pericardium which encloses the heart can be seen through
the mantle. Posterior and ventral to the pericardium is the brownish kidney. Note the anterior
and posterior adductor muscles which you cut to open your Mercenaria. Also identify the
retractor muscles which control extension and retraction of the foot. Water enters the mantle
cavity through the ventral inhalent siphon and exits via the dorsal exhalent siphon. The water
current is driven by the large, folded ctenidia which fill the bulk of the mantle cavity. Keep your
specimen under seawater when you are not looking at it so that it doesn't dry out.
Examine the shell you have removed from your specimen (see p. 238, S&S). On the
outside is the thin proteinaceous periostracum especially apparent at the hinge. By breaking the
shell you can be in middle, prismatic shell layer composed of calcium carbonate plates and
protein. The inside shell layer, the nacreous layer, is composed mostly of calcium carbonate.
Each of these shell layers is secreted by the mantle. The outer lobe of the mantle secretes both
the periostracum and the pismatic layer on the leading edge of the mantle, while the nacreous
layer is secreted by the entire mantle. Compare the shell structure of Mercenaria with the ribbed
mussel Geukensia. How do they differ? Can you relate these differences to the habitats of
The ctenidium of most bivalves serve both a respiratory and food gathering function and
are greatly enlarged when compared to the gills of other molluscs. For this reason, filter feeding
bivalves are termed lamellibranchs (plate gills). Most bivalves possess the single pair of
ctenidia found in the generalized mollusc, but each gill has been expanded to form a large
W-shaped structure. Try to verify this with your Mercenaria specimen. In filter feeding,
particles sieved by the gills are sorted to size by means of ciliated grooves and moved to the
labial palps which move food material into the mouth. Locate the ciliated food groove between
the labial palps and the slitlike mouth. Food is trapped in a mucus strand secreted by the
salivary glands and passed into the esophagus. From the esophagus, food passes to the stomach
which is surrounded by a large green digestive gland. An outpocketing of the stomach called
the style sac contains a gelatinous rod called the crystalline style. The style is composed of
enzymes and slowly revolves by style sac cilia to wind the mucus string into the stomach while
releasing its enzymes which begin the digestive process. The style may not be present in your
specimen since bivalves resorb their styles under harsh conditions. Digestion occurs in the
stomach and in the digestive gland. The remainder of the digestive tract consists of a long
intestine and an anus which opens near the exhalent siphon.
You should also be able to identify gonads, the heart, kidney, and cerebral ganglia in your
In all lamellibranch ("sheet gill") bivalves, the gill or ctenidium is typically W-shaped. It
is composed of numerous folded filaments which are connected to form sheets or lamellae, each
gill possessing four such lamellae. Each gill is positioned within the mantle cavity so that one
free arm of the W is connected to the mantle and the other free arm is connected to the foot or
visceral mass. Thus the gills effectively divide the mantle cavity into several chambers. The
large chamber below the gills is called the inhalent chamber while the cavities above the gills
are exhalent chambers.
Gills are usually considered to have respiration as their primary function. In
lamellibranch bivalves, however, a much larger surface area of gills is present than is actually
needed for gas exchange, and the gills have assumed additional functions. In freshwater
bivalves, for example, the gills are used as brood chambers where glochidia larvae are protected
until they are mature enough to be released. Finally, in addition to respiratory and reproductive
functions, perhaps the most important function of lamellibranch gills is in feeding.
All lamellibranch bivalves are filter feeders. Special cilia located between the gill
filaments produce water currents which move water into the inhalent portion of the mantle cavity
and up through the gills into the exhalent chambers. Particles of food or other suspended
material which are above a certain size are filtered from the water by gill cilia and accumulate on
the inhalent faces of the gill lamellae. This material is then moved by other cilia toward the
ventral edges of the gills (the bottom points of the W) where the food grooves are located. Once
in the food grooves, the food moves anteriorly until it reaches the palps, located on either side of
the mouth. Here again sorting is carried out on a size basis. Fine material is carried by cilia
into the mouth. Coarser particles accumulate at the edges of the palps and are periodically
thrown off by muscular twitches onto the mantle wall. This material which has never entered
the gut is usually called pseudofeces. The pseudofeces are eventually expelled from the mantle
cavity by spasmodic contractions of the adductor muscles which force wate and the accumulated
pseudofeces out through the normally inhalent opening or siphon.
It should be noted that the anal opening (where true feces are released) and the renal and
genital openings are all located in the exhalent portion of the mantle cavity. Thus, expulsion of
wastes and of reproductive products is accomplished by the normal, continuous flow of the
feeding current, leaving the animal via the exhalent opening or siphon.
Obtain a fresh Mercenaria or Geukensia specimen and open it as described previously
being careful not to damage the gills. Place your clam on a halfshell in a dish of seawater and
carefully lift the free edge of the mantle to expose the gills and palps. Examine the gills under a
dissecting microscope and then by adding carmine particles trace the movement of suspended
material from the gills to the palps. Small pieces of aluminum foil may be used to examine the
rejection of larger particles. After you have done this, carefully cut a couple small strips of
tissue from the leading edge of the ctenidium and mount them (using saltwater) on a slide and
examine them under a compound microscope. Describe what you see.
Bivalves locomote in a number of ways. The most common method is burrowing, where
the muscular foot is used to anchor and pull the clam into the substrate. Some bivalves such as
the razor clam, Ensis, do this quite well. If available, obtain a live Ensis specimen and place it
in a plexiglass burrowing chamber filled with soft sand. The burrowing chamber should allow
you to examine how burrowing is accomplished. Describe a typical burrowing movement
sequence in Ensis. Do the same with Mercenaria and compare your observations.
A number of bivalve species attach and move on hard substrates using byssal threads
which are secreted by pedal glands and attached by a small modified foot. Mytilus and
Geukensia are examples of bivalves with this life style. Examine the byssal thread attachment
of these species in the aquaria. Do these mussels respond to stimuli or are they entirely sessile?
Obtain a small (~lcm) mussel from the aquaria and place it in a fingerbowl of seawater.
Examine it under a dissecting microscope. Can you identify the foot? Set the mussel aside for
a while and then reexamine it. Is the foot extended? Has the foot begun to secrete byssal
threads? Make sure that the edge of the shell is in close contact with the surface so that byssal
attachment is possible.
Some bivalves such as scallops, Pectin, swim by rapidly opening and closing their valves
creating a water jet. Observe this in the aquaria by locating an Aequipectin specimen and
draping it through the water. What structures are responsible for opening and closing the valves
in swimming? If starfish are available in the aquaria, see if they stimulate escape swimming in
Aequipectin. To do this properly you will want to discriminate between a chemosensory and
tactile escape response.
Cephalopods are easily the most advanced molluscs, or invertebrates for that matter, and
their relationship to other molluscs is not immediately obvious. In contrast to other molluscs the
head and foot of cephalopods has become fused to form the cephalized anterior end, and there
has been a tendency towards reduction and loss of the shell. The adaptive radiation of
cephalopods can be viewed as a response to their taking up an active, pelagic, predatory life style.
Since cephalopods are rather expensive (live or dead) and are not readily available in the
local area, we will have to restrict our examination of cephalopod in the laboratory to a dissection
of the squid, Loligo. In performing the dissection, you will want to refer to pages 240-241 of
S&S for diagrams.
Obtain a pickled specimen of Loligo and place it in a wax bottomed dissecting pan.
Notice the streamlined shape of the squid and the presence of lateral fins. While carrying out
your dissection, keep in mind that Loligo is an active, free-swimming predator and relate this life
style to the design of the animal. The viscera of the squid are completely enveloped by a thick
mantle, the free edge of which forms a collar about the neck. The head bears a pair of complex
eyes. The head is drawn out into 10 appendages--four pairs of arms, each with two rows of
stalked suckers, and one pair of long retractile tentacles, with stalked suckers only at the ends.
The tentacles shoot out to catch the prey. The arms hold the prey while it is eaten. Examine the
structure of the suckers under a lens. In the mature male the left ventral arm (hectocotylus) is
modified for transferring spermatophores to the female. On this arm the distal suckers are
replaced by long papillae.
The mouth lies within the circle of arms. It is surrounded by a peristomial membrane,
around which is a buccal membrane with seven projections, each with suckers on the inner
surface. In the mature female there is a small pouch or sperm receptacle on the buccal
membrane in the median ventral line, one of the places where the male may place the
spermatophore. The female uses one of her arms to pick up strings of eggs as they come from
her siphon, fertilizes them with spermatozoa from the pouch, and then attaches the strings to
some object in the sea. Probe in the mouth to find two horny beaklike jaws.
A muscular siphon (funnel) usually projects under the collar on the ventral side, but it may
be partially withdrawn. Water forced through the siphon by muscular contraction of the mantle
furnishes the power for the "jet propulsion" locomotion that carries the squid backward through
the water. Wastes, sexual products, and ink are carried out by the current of water than enters
through the collar and leaves through the siphon. The siphon of the squid is not homologous to
the siphon of the clam; the clam siphon is a modification of the mantle, wherea the squid siphon,
along with the arms and tentacles, is a modification of the foot
The mottled appearance of the skin is due to chromatophores—irregularly shaped
pigment cells, to which radiating muscle fibers are attached. The spreading of the pigment
throughout the cells causes darkening of the skin; the concentration of the pigment lightens the
skin color. The squid can change from almost white through shades of purple to almost black.
Of what adaptive advantage is this to the squid?
Beginning near the siphon, make a longitudinal incision through the mantle from the collar
to the tip. Pin out the mantle and cover with water. The space between the mantle and the
visceral mass is the mantle cavity. Find a cartilaginous structure on each side of the siphon and
similar structures on the inside of the mantle. These interlocking pieces of cartilage help support
the siphon and close the space between the neck and the mantle during jet propulsion. There are
other cartilages in the head, fins, etc.
Lateral to the siphon, find large saclike valves that prevent outflow of water by way of the
collar. Slit open the siphon to see the muscular tonguelike valve that prevents inflow of water
through the siphon. Note the large pair of retractor muscles of the siphon and beneath them the
large retractor muscles of the head. Locate the free end of the rectum with its anus near the
inner opening of the siphon. Between it and the visceral mass is the ink sac. Do not puncture
it. When endangered, the squid sends out a cloud of black ink through the siphon as it darts off
in the opposite direction.
A pair of long gills (ctenidia) are attached at one end to the visceral mass and at the other
to the mantle. A thin skin covers the organs of the visceral mass and encloses the coelom.
Remove this membrane carefully as you expose the visceral organs. If the specimen if a female,
a pair of large whitish nidamental glands (which secrete the outer capsules of the egg masses)
should be carefully removed. Note their location and lay them aside for later study.
Respiratory and circulatory systems:
At the base of each gill is a small whitish bulblike branchial heart (gill heart). Blood
from the branchial heart is carried to the gill by an afferent branchial vein and returned by an
efferent branchial vein to the systemic heart, a larger whitish organ lying between the branchial
hearts. Each of the branchial hearts receives the blood from a large conical posterior vena cave
as well as from a fork of the anterior vena cave (cephalic vein). The systemic heart pumps
oxygenated blood through the cephalic aorta (anterior) and the short posterior aorta, which
branches to form medial and lateral mantle arteries.
A pair of kidneys, somewhat triangular in shape and usually white or pale in uninjected
specimens, lie between and slightly anterior to the branchial hearts. The kidneys will take up the
color of an injection fluid, if used. A renal papilla lies at the anterior tip of each kidney.
Remove the siphon by first cutting the siphon retractor muscles and then the lateral
siphon valves and the two small protractor muscles. Cut between the two ventral arms to
expose the pharynx (buccal bulb). Cut away the buccal and peristomial membranes to expose
the chitinous jaws. Dissect away the overlapping lower jaw and bend back the tonguelike ligula.
Note the radula with its rows of minute teeth. Remove the radula and examine under a
microscope, sketching the arrangement of the teeth.
The esophagus leads down through the liver, a soft pale organ lying between the head
retractor muscles. It emerges from the posterior end of the liver, passes through the pancreas,
and leads to the thick-walled muscular stomach, lying back somewhat posterior to the visceral
heart. The stomach communicates directly with the cecum, a thin-walled sac that may, when
filled with partly digested food, be quite large. The intestine leaves the stomach near the
entrance of the esophagus and passes anteriorly to the rectum and anus. Open and rinse out the
cecum and examine on its ventral surface the fan-shaped spiral valve, a complex device for
sorting food particles.
The ink sac is a diverticulum of the intestine located back of the rectum and anus. It
secretes a dark fluid of melanin pigment that is carried to the rectum by a short duct.
Push the head to one side to see a pair of large stellate ganglia on the inner surface of the
mantle close to the neck. These ganglia function in the movement of the mantle. From each
ganglion several large nerve radiate out over the inner mantle surface. Each nerve contains,
along with smaller fibers, one of the giant fibers which are used in rapid maximal contracl of the
mantle. Directions will not be given here for dissection of the brain, which is composed of
ganglia lying partly above and partly below the esophagus.
Sense organs of cephalopods are highly developed. The eyes are capable of forming an
image. Remove the thin outer transparent integument (false cornea) to uncover the true cornea.
Cut away the cornea to observe the circular iris diaphragm. Behind the iris is the almost
spherical lens, suspended by a ciliary muscle. Remove the lens to see the darkly pigmented
sensory lining (retina) of the optic cavity. Sensory cells are numerous in the skin, particularly in
the rims of the suckers. Statocysts are found embedded in the cartilages on each side of the
In the male, the testis is an elongated light-colored organ in the posterior end of the
coelomic cavity. It may be concealed by the cecum. Spermatozoa are shed into the coelom
from an opening in the testis. They then travel up the vas deferens. The vas deferens connects
to the spermatophori gland, which produces substances which "package" the sperm into
spermatophores. These spermatophores are stored in the spermatophoric sac. During
copulation the hectocotylized arm (left ventral) takes the spermatophores from the genital
opening at the tip of the penis and transfers them to the female.
In the female the nidamental glands are conspicuous white organs filling most of the lower
part of the mantle cavity. You have probably already removed them. The ovary lies posterior
and sheds eggs into the coelomic cavity. Push the ovary to one side and try to locate the oviduct
(it may be covered by the cecum). Near the left branchial heart the oviduct enlarges into the
oviducal gland, which secretes the individual egg cases. The oviduct continues anterior! beside
the nidamental glands to its flared opening, the ostium, in the mantle cavity. In the process of
mating the male may thrust the spermatophores inside the female's mantle cavity, or into the
sperm receptacle near her mouth. When the eggs have been fertilized, a gelatinous matrix is
secreted around them. The female holds this gelatinous mass within her arms until she finds a
rock or othe suitable object to attach it to. The young squid hatch in 2-3 weeks.
Dissect out the chitinous pen that lies dorsal to the visceral organs and extends from the
free edge of the collar to the apex of the mantle. There are also a number of cartilages in the
head, near the siphon, and in the mantle.
LABORATORY 8: PHYLUM ARTHROPODA
In numbers of species, the phylum Arthropoda outranks all other phyla, comprising over
three fourths of all animal species. Arthropod body organization is obviously a successful one.
Extreme structural flexibility and a high capacity to speciate are also implied by these numbers.
The success of the phylum is obvious, whether measured by numbers of individuals, species,
total biomass, structural variety, adaptability, or evolutionary plasticity.
The basic arthropod body type is characterized by: 1) bilateral symmetry; 2) segmentation;
3) a hardened exoskeleton, usually chitinous; 4) jointed appendages; 5) a strong tendency toward
the fusion of blocks of segments to form major body regions (head, thorax, and abdomen)
referred to as tagmosis; 6) a strong tendency toward the formation of specialized segments and
appendages; 7) no distinct trochophore-like larva; 8) discontinuous apparent growth, usually
occurring immediately after shedding the exoskeleton (molting); 9) cephalization; 10) coelom
reduction and the formation of a haemocoel; 11) retention of many annelid characters [dorsal
heart with ostia, nerve ring around esophagus; ventral ganglia paired (primitively) in each
The major groups of arthropods are classified according to their segmentation tagmosis,
and appendage differentiation. One of the most important aspects of arthropod biology is the
extraordinary impact that the chitinous exoskeleton has had on the form, function, adaptability,
and evolution of the group. Not only the name arthropod (jointed feet), but most other
characters such as the manner of growth, circulatory and respiratory systems, size, musculature,
and even habitat can be related to living within a tough, jointed, hollow skeleton. Keep this in
mind in your examination of representative arthropods.
Any comparative study of arthropods is difficult, since its major elements become
diversified before the earliest recognizable fossils were deposited in the cambrian, 500 million
years ago. Arthropod diversity is so vast that innumerable examples are required to get any
feeling at all for the patterns of change and groups that have evolved during this long period.
We will have time today to study very few examples, but these will hopefully provide a brief
introduction to some of the major patterns of arthropod adaptation.
Classically, two major groups of living arthropods are generally recognized: the
MANDIBULATES, which are jawed or mandible-bearing; and the CHELICERATES whose first
appendages bear claw-like pincers. This dichotomous division of arthropods probably does not
have evolutionary significance and each of these groups is probably polyphyletic. In our work
we will recognize four arthropod subphyla 1) Trilobitomorpha (extinct trilobed arthropods); 2)
Chelicerata, which are arthropods whose first appendages are claw-like pincers and include the
classes Arachnida (scorpions, spiders, mites, and ticks), Merostomata (horseshoe crabs) and
Pycnogonida (sea spiders); 3) Crustacea which all have two pairs of antennae, biramous
appendages and include crabs, lobsters, shrimp, barnacles, and a variety of small aquatic forms;
and 4) UNIRAMIA which have uniramous appendages and include the classes Insecta which all
have bodies divided into head, thorax, and abdomen with three thoracic pairs of legs, Chilopoda
which have body divided into head and trunk with each trunk segment having one pair of
appendages (centipedes) and Diplopoda which have body divided into a head and trunk with two
pairs of appendages on each trunk segment (millipedes). A simplified key to the classes of
arthropods is given below. You should examine it carefully and use it to classify each of the
specimens you look at in today's lab.
KEY TO CLASSES OF PHYLUM ARTHROPODA
la. Arthropods with body divided by two longitudinal furrows into three distinct lobes;
appendages (2 per segment) are numerous and similar; now extinct,
known only as fossils. (Subphylum Trilobita)…………………………Trilobite fossil
lb. Arthropods without the above combination of characteristics……………………… 2
2a. Without jaws and antennae; first pair of ventral appendages are chelicerae
(Subphylum Chelicerata)………………………………………………………………. 3
2b. With jaws (mandibles) and antennae (Mandibulates)…………………………………. 5
3a. Possessing abdominal appendages and a long spike-like
telson……………………………………………………………….. Class Merostomata
3b. Lacking the above characteristics……………………………………………………… 4
4a. Body divided into cephalothorax and abdomen with a very large abdomen; four pairs of
walking legs present on cephalothorax …………….…………………. Class Arachnida
4b. Body divided into cephalothorax and abdomen with a very reduced abdomen; four to six
pairs of walking legs present on cephalothorax ……………………... Class Pycnogonida
5a. Possessing gills, biramous appendages and 2 pairs of antennae..………. Class Crustacea
5b. Possessing one pair of antennae and no gills in the adult form………………………….. 6
6a. Body divided into head, thorax and abdomen; 3 pairs of legs on thorax
……………………………………………………………………………… Class Insecta
6b. Body divided into head and trunk; numerous trunk appendages………………………... 7
7a. Possessing one pair of appendages on each trunk segment; first pair of trunk appendages
(maxillipeds) are poison claws………………………………………….. Class Chilopoda
7b. Possessing 2 pair of appendages on each apparent trunk segment
…………………………………………………………………………... Class Diplopoda
GLOSSARY OF SOME TERMS USED IN THE IDENTIFICATION OF ARTHROPODS
Abdomen - The most posterior of the major body divisions.
Antennae - The most anterior head appendages of mandibulate arthropods. In crustaceans,
which possess 2 pairs of antennae, the first pair are called antennules and the second pair are
referred to as antennae.
Biramous - (adj.) Having two branches. Refers specifically to the two-branched condition of
typical crustacean appendages.
Carapace - The part of the exoskeleton covering all or a portion of the cephalothorax. It is
formed from the fusion of a number of individual skeletal plates.
Cephalothorax - A major body division formed by the fusion of the head and thorax.
Chelicerae - (sing. chelicera) The first pair of appendages on the cephalothorax of chelicerate
arthropods; they are typically pincer-like.
Mandible - One of a pair of mouth appendages comprising a jaw in mandibulate arthropods.
Telson - Terminal segment-like part (not considered a segment proper) of an arthropod, which
bears the anal opening. In horseshoe crabs (Class Merostomata) the terminal spike-like tail is
called a telson, but it is not homologous to the telson of other arthropods.
Trunk - Portion of the body behind the head, consisting of a thorax and abdomen that cannot be
In today's laboratory we will examine a variety of representative arthropods in order to get a feel
for their form, function, and classification.
Obtain a living or preserved specimen of the horseshoe crab Limulus and examine its
external anatomy (refer to pg. 179, S&S). On the dorsal surface note that the body is divided
into an anterior prosoma and a posterior opisthosoma which terminates in a telson. The
prosoma is composed of eight fused segments and carries the walking legs and chelicera. On its
dorsal surface examine the simple and compound eyes. The opisthosoma houses the
reproductive organs and book gills. The telson is used to right the body when overturned and in
forward locomotion. On the ventral surface of the prosoma examine the appendages of Limulus.
The clawlike chelicerae are located on the second prosomal segment, the third segment bears a
pair of pedipalps and segments four through seven nave ambulatory legs. On the eighth
prosomal segment are located a pair of flat chilaria, whose function is unknown. On the base of
the walking legs note the presence of masticating structures called gnathobases. The ventral
surface of the opisthosoma bears six pairs of segments which are all fused at the midline to form
flattened plate-like flaps, with each having an endopodite and exopodite division. The first flap
is the genital operculum with paired genital opening on its posterior surface. On the posterior
surface of the exopodites of the remaining five limbs are leaf-like gills termed a gillbook. The
final two opisthomal segments are fused and limbless.
Be sure you can key Limulus to class using the key at the beginning of the handout.
Limulus lives on soft bottoms and is a carnivore/scavenger. Food is moved into the mouth
region with the chelicera and walking legs and then ground by the gnathobases before entering
the mouth. To observe this, place a small Limulus in a plastic aquaria and present it with some
clam tissue. Describe your observations.
Carefully observe and describe the locomotion pattern of Limulus. What appendages are
used? How are the appendages modified for this locomotion pattern?
Obtain living or preserved specimens of a representative terrestrial chelicerate. We may
have spiders or scorpions, or both. Using the key at the beginning of this exercise, key them to
class. Examine these specimens referring to pages 180 and 183 in S&S. On the ventral surface
of your specimen, identify the piercing chelicerae, the pedipalps which are used for grasping
prey, and the walking legs. Terrestrial chelicerates have respiratory organs (book lungs) on the
opisthosoma which are considered by most biologists to have been derived from book gills.
Locate the opening to the book lungs on your specimen. Anesthetize your specimen in alcohol
(if live) and then peel away the cuticle and examine the book lungs under the dissecting
microscope. In some spiders silk glands and spinnerets will be seen behind the lungs.
Like other arthropods, the coelom of Limulus is filled with perivisceral sinuses which
constitute a hemocoel. The vascular system is open, consisting of arteries that discharge blood
into the sinuses rather than into capillaries and veins. The blood surrounds and bathes the
tissues and organs of the body. Blood eventually collects in the large pericardial sinus
surrounding the heart. The heart is perforated with ostia, through which blood enters from the
perivisceral sinus. The ostia have one-way valves so that when the heart contracts, blood is
forced into the arteries with no backflow. The blood of Limulus as with most arthropods may
function in transportation of food and gases, as well as being involved in phagocytic and clotting
reactions. The copper containing pigment haemocyanin is the respiratory pigment found in
Limulus, while haemoglobin is found in some insects and crustaceans.
Limulus blood removal procedure:
With a syringe, carefully remove a small amount of blood (~1 ml) from the heart of your
Limulus (See p. 193 of S&S for directions). Examine the blood under the microscope. Can you
observe blood cells? Does it clot? Inject a small amount of India ink (~1 ml) into the heart of
your Limulus. After about an hour you can reexamine the blood to see if the ink particles have
been phagocytized. The India ink injection should also allow you to see the blood circulatory
system in the book gills and the rest of the body.
Crustaceans are an extremely diverse group of primarily aquatic arthropods characterized
by having biramous appendages and two pairs of antennae. We will systematically examine a
variety of representative crustaceans.
Class Branchiopoda (gill feet). Possess four or more pairs of thoracic appendages which are
leaf-like (flattened) and are provided with gills on their margins. Antennae are either adapted
for swimming or reduced in size. Mostly freshwater organisms.
Order Anostraca (no carapace). Body long and slender with 11-19 pairs of thoracic
appendages and stalked eyes. Fairy shrimp and brine shrimp belong to this order. They swim
upside down, using their appendages for propulsion, respiration, and filter feeding.
Obtain a large Artemia (brine shrimp) specimen and examine it in a small watch glass.
How does it move? Describe your observations. To get a closer look, mount a large Artemia
ventral side up on a depression slide and examine under a dissecting scope. Can you see the
gills? Describe the structure of the thoracic appendages. How many different types of
appendages do you see? What is the function of each? To examine the feeding mechanism,
introduce a drop of congo-redstained yeast suspension into the depression. How is the food
collected? How is it moved to the mouth? This is thought to be the primitive crustacean
Class Ostracoda (see shrimp). Body 1aterally compressed with a disproportionately large head
with well-developed antennae used for locomotion. The trunk appendages are generally reduced
to two pairs.
Obtain some ostracods and examine them under the microscope. Describe how they move
and observe their feeding by giving them congo-red-stained yeast.
Class Copepoda. Body small and cylindrical, ocelli fused to form a single median eye; no
appendages on abdomen; thoracic appendages used in propulsion; first antennae are enlarged and
function to prevent sinking when the thoracic or second antennae stop moving; freshwater and
marine. Females are often seen carrying egg sacs between the thorax and abdomen. These are
perhaps the most common organisms on earth being the primary herbivores that feed on marine
phytoplankton. Some, however, are carnivorous and feed raptorially on other copepods.
Examine some copepods under the microscope on a depression slide. Use the diagrams in
Barnes to identify body structures. Describe locomotion and feeding using a congo-red stained
Class Cirripedia (barnacles). Sessile, either stalked or attached directly to the substratum; first
antennae are vestigial except for the cement glands; second antennae present only in larva; six
pairs of thoracic appendages (cirri) modified for feeding; body covered by calcareous plates;
exclusively marine. Examine some live Balanus under the dissecting microscope in a
By introducing a small amount of a 3:1 milk : water suspension into the watchglass you
should be able to observe and describe the feeding movements. If time permits you may want to
dissect an acorn or gooseneck barnacle to convince yourself that it is indeed an arthropod. Are
the appendages segmented? Describe the structure of the shell. How does a barnacle grow?
Class Malacostracea Trunk portion of the body composed of 14 segments, 8 thoraci and 6
abdominal, appendages on all segments, compound eyes usually stalked.
Order Amphipoda Carapace absent and body usually laterally compressed; gills and
heart located in thorax; appendages show a high degree of differentiation; brood pouch.
Commonly called "scud." Examine the amphipods available in the laboratory. Refer to Barnes
for diagrams. Locate the brood pouch, gills, and try to determin the function of the various
appendages. Try to observe amphipod feeding using detritus from the aquaria.
Order Isopoda. Carapace absent and body usually dorsoventrally flattened; gills and
heart located in the abdomen; appendages show little differentiation. Examine the isopods
available in the laboratory. Refer to Barnes for diagrams. How have isopods become adapted
for a semiterrestrial existence? How is locomotion accomplished in isopods? How does this
differ from amphipods?
Order Decapoda First three pairs of thoracic appendages are modified as maxillip' the
remaining 5 pairs of thoracic appendages are legs (Decapoda = ten legs); carapace present and
generally well-developed. This is the largest crustacean order and contains shrimp, lobsters,
crabs etc. We will examine a number of decapods in the laboratory today.
Obtain a live or preserved specimen of the crayfish, Cambarus. We will use Cambarus to
illustrate basic crustacean anatomy. It represents a relatively primitive decapod crustacean.
The crayfish is a common inhabitant of freshwater streams and ponds. Crayfish feed chiefly on
detritus, although they can use their claws to break open poorly armoured shells. Observe a
crayfish in a plastic aquaria dealing with some pieces of clam meat. Watch it locate the food
with its antennae, tear off chunks with its chelipeds, tease it apart with its mandibles and finally
pass the smaller pieces to the mouthparts (maxillae and maxillipeds). Refer to pages 176 & 177
of S&S for illustrations. Observe walking, swimming, and respiratory movements. Which
appendages are used in each process? How are the appendages modified for each function? To
observe the respiratory current you car add a couple drops of India ink near the crayfish while it
sits in a fingerbowl.
Using a pickled Cambarus, closely examine the segmentation and appendages. The
segments are grouped into three general regions: 1) head (segments 1-5 with antennae,
mandibles, and 2 pairs of maxillae); 2) thorax (segments 6-13, with 3 pairs of maxillipeds, 1 pair
of chelipeds, and 4 pairs of walking legs) and 3) abdomen (segments 14-19 with 5 pairs of
pleopods and a uropod and telson). Are all the appendages jointed? How do the chelipeds
operate? Remove one and examine the musculature. Examine the functional anatomy of the
Starting from the anterior end of your specimen try to identify and assign a function to the
19 pairs of appendages. Remember that in the primitive condition (Artemia) little specialization
is seen and the appendages are all similar. Each limb primitively consists of three portions: the
protopod or stem, the inner endopod, and outer exopod. Examine and attempt to explain how
and why modification of this basic plan have occurred.
Locate the major body openings including the mouth, anus, the excretory pore on each
antennae, and the genital pores. The male genital ducts open at the base of the last leg. A
trough for the transfer of spermatophores into the female seminal receptacle is formed from the
fused first and second swimmerets. The oviducts open at the base of the second walking legs,
while a pore at the base between the fourth walking legs serves to receive spermatophores. The
first swimmeret in females is reduced or absent. The female telson and filamentous swimmerets
hold the egg cluster to form an external brood pouch for the eggs and young.
Carefully cut away the laternal extension of the carapace covering the gills, the
branchiostegite, from one side to expose the internal sheet of gills. Now make the dorsal and
lateral cuts indicated on page 177 of S&S (Fig. 7.5E) and carefully remove the dorsal
exoskeleton of the thoracic and abdominal regions. Once you have opened your specimen,
examine its internal structure referring to the diagrams on pages 196 and 197 of S&S.
The statocysts of most crustaceans are located on the base of the antennules. Remove an
antennule from your preserved Cambarus and try to locate and examine a statocyst. Statocysts
function in response to gravity and enable the animal to orient itself. Removal of one or both
statocysts from living crayfish demonstrate this well. If anyone is inclined to try this, there are
directions on the top of page 209 of S&S.
Once you have thoroughly examined the crayfish you should take a look at the external
anatomy of the other decapod crustaceans available in the laboratory. Examine the external
anatomy of the Brachyuran (true-crabs) crab Carcinus. How does it differ from Cambarus?
Try to identify the appendages. What has happened to the abdomen? Why? How can you
quickly tell a male from a female brachyuran crab? Why this difference? Observe the
ventilation current of Carcinus using India ink. Is it similar to Cambarus? If any Cancer are
available, examine its ventilation current. What is the function of the fine hairs on the limbs
covering the inhalent opening?
Examine the anatomy of one of the hermit crabs (all Pagurus sp.) available in the
laboratory. To remove the crab from its shell you can gently heat the apex of the shell. If it
doesn't work immediately, ask for help. How does the segmentation and appendages of Pagurus
compare with Cambarus and Carcinus? How is Pagurus well-adapted morphologically to
living in shells? How are they like the original gastropod owners of the shell morphologically?
What is the advantage of inhabiting a shell and how could it have evolved? If time permits or
frivolity prevails we will "arrange" some ritualized shell fight encounters between crabs. This
can be easily done by placing a small crab in a larger shell than a larger crab. The larger crab
will usually respond to this injustice by provoking a fight with the smaller crab and evicting it
from its superior home. The fight, however, is ritualized avoiding injury to either party. What
is the advantage of a ritualized fight?
The subphylum is made up of three arthropod classes which have a single antennae and
uniramous segmental appendages. The classes are 1) Chilopoda which have a body divided into
a head and trunk with the trunk bearing many segments, each with a single pair of appendages.
(= centipedes). 2) Diplopoda which have a body divided into a head and trunk with the trunk
bearing many segments that each have two pairs of appendages (millipedes). These first two
classes are usually referred to as the Myriapoda. and 3) Insecta which have a body divided into
a head, thorax, and abdomen with three pairs of legs on the thorax.
Examine preserved specimens of the two myriapod classes. Pay particular attention to
the differentiation and basic form of the appendages. See S&S page 172.
To examine basic insect design, we will look at the grasshopper, Romalea. Obtain a
preserved Romalea and place it in a wax-bottomed pan. Romalea is a hemimetabolous insect,
which means that it goes through a gradual metamorphosis from larva to adult. This is in
contrast to holometabolous insect which has complete metamorphosis divided into four distinct
stages: egg, larva, pupa, and adult.
Identify the major body segments on your Romalea, the head, thorax, and abdomen.
How do these body divisions compare to those of the crayfish? The insect exoskeleton is a
complex, many-layered structure of chitin and other materials and is covered by a thin but
critically important outer waxy layer that prevents desiccation. The head consists of six fused
segments; the thorax consists of three segments, and the abdomen of eleven, including the
terminal reproductive organ. The tendency toward segment fusion is marked in insects.
Movement is restricted to soft joints between the segments. Apparent growth is limited to
stretching during the brief period from molting of the old exoskeleton and hardening of the new
Closely examine the head. Locate the compound eyes and simple eyes between them.
Using the diagrams on pages 174 and 175 of S&S identify the appendages, mouth parts and other
details of Romalea anatomy. In doing this try to relate form to function.
To examine the internal structure of Romalea, pin your specimen to a dissecting pan
through the base of the legs after trimming off the legs and hind wings. Carefully open the
dorsal surface of the abdomen and examine the internal organs. This is extremely difficult in
preserved specimens, but do your best using the diagram on page 175 of S&S.
The air-tube or tracheal system is an extremely important anatomical feature of insects
which allows them to breath in a dry environment. It supplies oxygen from the outside air
directly into the tissues and cells without a blood carrier, unlike most other animals. In this
rapid gas exchange by diffusion air flows through major tubes and numerous smaller branches
that penetrate tissues and reach each cell. If all but the trachea of the insect were taken away,
you would see remaining a tight network of fine interlacing branches reaching around the cells,
just as capillaries do in our own bodies. Air passes from the spiracles (openings) to the major
tracheal ducts, then to air sacs and a multitude of smaller tubes. Remove a bit of muscle tissue
from your Romalea, place it in a drop of water on a slide, tease it apart with needles, and then
press a coverslip over it. Examine this preparation under to observe the tracheal branches
among the muscle fiber.
One of the most interesting aspects of insect diversity is the variety of mouth parts that
have evolved to tap different food sources. Read the section in S&S (pages 186-189) dealing
with mouthpart diversity and examine the prepared slides of mouthparts available in the
LABORATORY 9: PHYLUM ECHINODERMATA
The phylum Echinodermata is clearly separated from all other phyla. Its members are
coelomate, and the coelom is of great importance not only in carrying and distributing nutrients,
respiratory gases, excretory and storage products but also in functioning as a water-vascular
system. The water-vascular system operates the hydraulic, extensible tube-feet which are
diagnostic of the phylum and which play an essential role in the life processes of these animals
and their interaction with the environment.
Echinoderms comprise a large phylum of specialized marine organisms that are
interesting for both their striking body form, their deuterostome characteristics and phylogenetic
position as precursors to the vertebrate line. Though adults of most echinoderms show radial
symmetry, this does not ally them with the Cnidaria. The radial symmetry of echinoderms is a
secondary characteristic associated with their sessile or creeping lifestyle. The larval stages of
echinoderms are actively swimming bilaterally symmetrical animals.
Most echinoderms have a calcite skeleton. In some, such as ophioroids (brittle stars), the
skeleton is in the form of rods supporting arms and other projections; in others, such as asteroids
(starfish) and echinoids (sea urchins), it forms a more-or-less rigid capsule; finally, in others,
such as holothuroids (sea cucumbers), it is highly reduced and represented only by isolated
spicules in the integument. The skeleton is generally not solid, but is built as a crystalline calcite
meshwork, with living protein material permeating the crystalline framework. The better-known
members, such as sea urchins, brittlestars, and starfish, have skeletal spines to which the name
Echinodermata (spiny skinned) refers. But possession of spines is not diagnostic of the phylum.
The earliest echinoderms were thought to be cup-shaped animals with a five-part
symmetry (pentamerous), and a sessile lifestyle with the mouth uppermost and the arms held out
radially to catch food. The crinoids (aea lilies) are the only extant group to retain this primitive
form. From this form, two different patterns evolved: one (Asterozoa) showed radial growth
patterns as evident in starfish and brittle stars, while the other (Echinozoa) showed fusion of the
original radial appendage plan as seen in urchins and sea cucumbers. While the Asterozoa
universally retain radial symmetry, there is a tendency within the Echinozoa to assume a tertiary
bilateral symmetry. This is reflected in the worm-like body of holothuroids (sea cucumbers) and
in the heart shape of some irregular echinoids (urchins). Asterozoa and Echinozoa can be
considered subphyla of Echinodermata. Below I have outlined the classification scheme of
I. SUBPHYLUM CRINOZOA
Mouth uppermost, arms well-developed and often branching; sealilies and feather stars.
Crinoids are the most primitive echinoderms. Early fossil crinoids had stems, by which they
were attached permanently to the substrate, but subsequently the stem was lost so that the animal
could swim or crawl. The mouth is always directed upward and feeding is accomplished by
filtering with the arms. The arms are also used for swimming. Most crinoids are extinct, and
we will not he able to examine them in the laboratory.
II. SUBPHYLUM ASTEROZOA
Star-shaped; mouth on undersurface.
A. CLASS OPHIUROIDEA
Arms cylindrical and sharply demarcated from the central disc; brittle stars. Based on the
coelom and water vascular system, brittlestars are thought to be the group next most primitive to
the crinoids. They are also highly successful and probably outnumber all other classes of
echinoderms in number of species.
B. CLASS ASTEROIDEA
Arms not sharply demarcated from the central disc, well-developed water vascular system with
suction tube feet; starfish. Whereas the ophiuroids use their arms for propulsion over the sea
floor, asteroids rely on movements of the tube-feet for locomotion, and while ophiuroid skeletons
are fragile, asteroid skeletons are strong and capable of pulling apart bivalve shells.
III. SUBPHYLUM ECHINOZOA
Globose or worm-like, without radiating arms; some tertiary bilateral symmetry.
A. CLASS ECHINOIDEA
Skeleton consists of heavy plates which enclose the body in a rigid test. Sea urchins and sand
B. CLASS HOLOTHUROIDEA
Bilaterally symmetrical with an elongated oral-anal axis; skeleton reduced to ossicles in the
integument; filter and/or deposit feeding with modified oral tube-feet called buccal tentacles.
In today's laboratory we will have a chance to examine form and function in the common
Obtain a small specimen of Asterias forbesi and place it in a watchglass filled with
seawater for examination under the dissecting microscope. Carefully examine the oral and
aboral surfaces and identify the structures illustrated on pages 276 and 277 of S&S. The mouth
is located on the oral surface of the central disc, and radiating outward from the disc are five
arms or rays. Running down the center of each ray is the ambulacral groove with four rows of
tube feet. The roof of the ambulacral groove contains a radial nerve, which you may be able to
distinguish from the other tissue. Closely examine the structure of the tube feet which originate
lateral to the radial nerve. Try to watch a tube foot attach to a probe. Modified spines border
each ambulacral groove and the mouth. The ambulacral spines serve to protect the tube feet,
while the oral spines help move food into the mouth. Locate the rentacle at the end of each ray.
These tentacles are modified tube feet and have a sensory function. At the base of each tentacle
is located an eye spot which is light sensitive.
On the aboral side of your Asterias locate the conspicuous dome-shaped madreporite
which opens into the water-vascular system. The function of this perforated plate is uncertain.
It appears to function either as a device for ensuring equal pressure within the water-vascular
system and the external environment, or as a pressure receptor for providing information to the
tube feet about the changing head of water above the animal as the tide rises and falls. A small
anus is located in the interradius clockwise from the madroporlte. The rays on either side of the
madroporite are termed bivium arms and the remaining three arms are called trivium arms. The
aboral surface is covered by cilia and calcareous tubercles, spines, and beak-like pedicellaria.
Carefully place a drop of carmine suspension on the aboral surface to detect the movement of the
cilia. Is there a pattern to their movement? What is the function of these cilia? Also note the
small fleshy papulae (or dermal branchiae) which are protrusions of the coelom that emerge
between plates of the exoskeleton. They represent blisters of the external and coelomic epithelia
and contain coelomic fluid. The papulae, along with the tube feet, constitute the animal's
Pincer-like pedicellaria, which are modified spines, are distributed over the external
surface of Asterias (see page 298, of S&S). They function primarily in cleaning the surface and
ambulacral grooves, and protection of the papulae. Pedicellaria are composed of three modified
ossicles (skeletal plates). The basal ossicle forms a stable and the two distal ossicles oppose
each other with a shearing action like the blades of a pair of scissors. Study the aboral and oral
surfaces of Asterias and observe the form and distribution of pedlcellaria. Is there a functional
significance to the distribution of pedicellaria in Asterias? By pulling a strand of hair across the
surface of Asterias you should be able to see the pedicellaria in action. Remove some
pedicellaria and examine them under a compound microscope. You can clean them by placing
them in a drop of sodium hypochlorite solution. Are all the pedicellaria similar in form?
To examine the skeleton and ossicles of Asterias, remove a small piece of skin and boil it
in sodium hypochlorite. Examine the ossicles under the compound microscope and sketch them
so you can compare them with ossicles from the other echinoderm classes. The intact skeleton
of Asterias consists of articulating ossicles (plates) of calcite (calcium carbonate) held together
by leathery connective tissue. Be sure you closely examine the surface skeletal structure of
To observe the circulation of internal fluid in the coelom of Asterias, inject 0.5 to 1.0 ml
of a heavy carmine suspension in seawater into one of the rays of your starfish. Use a
hypodermic syringe with a 20 gauge needle. Observe how the color moves rapidly across the
ray and throughout the body. Examine the dermal branchiae under the microscope to detect
movement. How is this movement accomplished? After about 10 minutes, draw off a few
milliliters of coelomic fluid from the injected Asterias, and examine it under the compound
microscope. Where are the carmine particles located? Optimally, you should be able to
ascertain that internal circulation is caused by ciliary action and that foreign parcicles are quickly
removed from the coelomic fluid by amoebocytes.
Since starfish are rather slow-moving predators, it would be too time-consuming to try to
feed your Asterias. Hopefully, you will be able to observe this in one of the Asterias in the
holding tanks. Starfish are generally voracious predators which feed mainly on bivalves,
gastropods, and barnacles. They use their tube feet to secure prey or pry open the valves of
bivalves and then extrude their stomach on their prey, releasing enzymes, and then sucking up
the partially digested meal. Try to verify this with observations.
Using your injected Asterias or one of the starfish in the holding tank, describe the
locomotion pattern. How do the tube feet work? Are they coordinated with each other? Is
movement caused by the pushing or pulling of tube feet, or both? If time permits, you mav want
to perform some of the experiments on locomotion control in starfish outlined on page 295 of
Anesthetize your Asterias for dissection by soaking it in 7% MgCl for approximately 30
minutes. Do not contaminate any plastic dishes with chemicals. Always use glass containers
and wash them out thoroughly when finished. Once your Asterias is relaxed, remove part of the
body wall from the central disc and one arm (See page 276 & 277, S&S). Take care cutting
around the central disc, so that the madroporite and other surface structures and their internal
connections are not disturbed. It is best to remove the body wall from the arm opposite the
madroporite to avoid this problem. Try to identify the structures illustrated on pages 276 and
277 of S&S.
Trace out the path of the water vascular system. The madroporite opens into the stone
canal which leads to the ring canal around the esophagus. Tease around the digestive tract to see
these structures. On the edge of the radial canal are nine swollen areas referred to as
Tiedemann's bodies. Their function is uncertain, but they are thought to filter the water
vascular system of debris with the aid of the amoebocytes which are found concentrated there.
They are then much like the lymph nodes of vertebrates. Leading from the ring canal are five
radial vessels each running the length of a single ray. Along the radial vessels are located the
tube feet and ampulla. How do the tube feet work? What is the function of the ampulla?
Examine a prepared slide of a crosssection of a starfish ray to get a better look at the functional
organization of the water vascular system.
Now locate the structures of the digestive system (page 277, S&S). A short esophagus
leads from the mouth and connects to the stomach. The stomach ls divided into a globular
protrusible cardiac portion and an aboral pyloric region. Running from the pyloric portion into
each arm are a pair of hepatic caeca that function in digestion and food storage. The rectum runs
to the aboral surface from the pyloric stomach and exits via the aboral anus. Cardiac retractor
muscles control the protrusion of the cardiac stonach.
The testes or ovaries of Asterias are paired organs located in each ray. Asteroids are
dioecious. Each gonad is attached by a gonoduct to the exterior via a gonopore located at the
junction of the rays. Ovaries are generally reddish in color and testes are white or yellow.
Examine the ovaries under the compound microscope for male and female gametes. If they
appear to be in good shape, you might want to try to make some starfish of your own.
Obtain an Ophioderma specimen and place it in a fingerbowl of seawater for examination
under the dissecting microscope. Brittle stars are superficially similar to asteroids, but their long
sinuous arms are more distinctly set off from the central disc and they locomote and feed in an
entirely different manner. Identify the structures shown on page 278 of S&S. The mouth is
located in the center of the oral surface of the central disc and is surrounded by five triangular
jaws. The arms have reduced tube feet called tentacles that issue from between the skeletal
plates or shields of the oral surface of the arms. There is no ambulacral groove and the skeletal
plates are arranged so that the arms are flexible. On the edge of the central disc are located ten
pairs of genital bursae that store gametes. Note the rough nature of the spines, that are used for
gripping the substrate, and the absence of suctorial discs on the tube feet. How do brittle stars
move? Examine the aboral surface of Ophioderma. Can you locate a madroporite?
pedicellaria? dermal papulae?
The skeletal plates of the ophiuroid skeleton form a complete, rigid covering over the
central disc. The skeleton of the arms consists of two parts: an outer skeleton composed of
aboral, oral, and lateral shields, and an internal series of vertebral ossicles. This arrangement is
designed to allow the arms to move freely and enables the brittlestar to crawl rapidly and swim.
To examine the skeletal structure of Ophioderma, remove the distal half of an arm and place it in
sodium hypochlorite to clean. Examine and describe the skeletal plates. How are they designed
to allow movement? Try to observe both crawling and swimming movements. Some
brittlestars have feathery spines which allow them to swim quite effectively.
Ophiuroids are microphagous ciliary-mucoid feeders and may feed macrophagously as
well. Mucous glands in the integument produce a network of mucus on the surface of the arms,
and the mucus and food entrapped by it are moved by cilia, tube feet, and arms to the mouth.
They also sweep their arms over the substrate to capture larger food particles, which may be
brought to the mouth by flexion of the arms or by passage from podia to podia.
The feeding methods of brittlestars can be categorized as follows.
A. Microphagous methods:
1) Mucous net method. The animal assumes a feeding posture with arm tips raised and spines
spread. Mucous glands secrete strings of mucus which hang over the spines. The arms are
then swept through the water column and the plankton-laden net is moved to the mouth by
podia and/or cilia). 2)Surface film feeding. The animal will move its arms parallel to the
surface and particulate matter is picked up by the podia.
B. Acrophagous methods:
1) Arm-loop capture. The arms may flex around large particles and convey them directly to the
mouth; 2) Browsing. Rarely, an animal will move over the substrate directly picking up food
with its mouth; 3) Tubefoot capture. Intermediate sized particles are picked up by the tube feet
and passed directly to the mouth. Clearly, the availability of these feeding mechanisms provides
brittlestars with a wide diversity of food types and consequently they have been very successful.
Place your Ophiostoma in a fingerbowl and offer it pieces of chopped mussel in the
following sizes to detect different feeding modes: 1) 10 x 5 mm; 2) <2 mm squares, and 3)
finely-ground mussel. In hopes of observing a mucous net, introduce into the dish of seawater a
weak solution of toluidine blue so that the water is colored a faint blue.
In stark contrast to other echinoderms, holothuroids have assumed a worm-like shape, with
mouth and anus at opposite ends of a cylindrical body; but the basic pentameric structure of the
typical echinoderm is still evident. The former five-part symmetry is particularly evident in the
arrangement of tube feet and muscles. Obtain a specimen of Thyone and place it in a seawater
filled watch glass for examination (refer to page 285 of S&S for illustration). In sea cucumber
that burrow or are found on open surfaces, the body is cylindrical and elongated in the oral-aboral
direction. In most holothuroids, tube feet are restricted to the ventral surface, but this is not the
case with Thyone. Can you differentiate between the dorsal and ventral surfaces of Thyone?
Are the tube feet evenly distributed and all of identical structure. Locate the mouth, buccal
tentacles, and cloaca aperture. How many tentacles are present? The tentacles represent
modified tube feet and are used in feeding. Food is trapped on the tentacles and then are
withdrawn into the mouth. Try to feed your Thyone some small pieces of chopped mussel. If
you are patient you may be able to observe the slow opening and closing of the cloacal aperture.
This represents a breathing movement.
Holothuroids have the most reduced skeleton of all the echinoderm classes. It consists of
numerous isolated plates and spicules in the body wall. Calcareous plates, however, give
support to the mouth, cloaca, tentacles, madroporite, and ring canal. Examine the body wall of
Thyone under a dissecting microscope and cut out a piece of wall material to examine the
spicules. Boil the piece in sodium hypochlorite and describe the spicules. How do they
compare with the other ossicles you have seen.
Anesthetize your Thyone by injecting it with 5 to 10 ml of MgC1 . It should be relaxed
for dissection in about 30 minutes. To open your Thyone make a ventral incision from the
mouth to anus, open the incision, and pin the specimen to a dissecting pan. In cutting, be sure
you don't harm the internal organs. Compare your opened specimen to the diagram on page 285
of S&S. Identify the dorsal madroporite and stone canal, which hang free in the coelom. The
stone canal connects to the water vascular ring canal, which surrounds the esophagus. The ring
canal has two elongate sacs called polian vesicles which are thought to be reservoirs of water
vascular fluid. From the ring canal, radial canals run anteriorly to the oral tentacles, and then
turn back as posterior branches that are embedded in the longitudinal muscle bands and give rise
to the tube feet. Five paired bands of longitudinal muscles run the length of the body wall. At
the anterior end retractor muscles, attached to a calcareous ring function to pu the tentacles into
the body. Circular muscles line the body wall and are thickened as sphincters around the mouth
Locate the respiratory trees, which are the two large branching organs that lead out of the
terminal end of the intestine. These are the structures that are ventilated by the cloacal breathing
of Thyone. The red color of the respiratory trees should tell you that they contain hemoglobin as
an oxygen carrier.
Identify the components of the digestive system, including the mouth, pharynx, esophagus,
stomach, intestine, and cloaca. Can you determine the feeding mechanism of holothuroids by a
close examination of the tentacles? Examine the contents of the stomach and intestine for
parasites and commensals.
Obtain a Strongylocentrotus specimen and place it in a fingerbowl of fresh water for
examination. Refer to pages 280-282 of S&S for illustrations. Examine the oral surface and
locate the mouth which bears five protrusible teeth used for scraping and chewing algae. A soft,
membranous area called the peristome surrounds the mouth and has modified buccal tube feet
which have a chemosensory function. At the edge of the peristome are five pairs of gills that
are evaginations of the body wall that communicate with the coelom and are thought to have a
respiratory function. On the aboral surface locate the periproct, madroporite and genital
plates. The genital plates are perforated and provide exit for the gametes. Between each
genital plate is an ocular plate which has a single pore through which a modified light-sensitive
tube foot/tentacle emerges.
Examine the surface of your urchin under the dissecting scope. Note that the entire
external surface is ciliated. Why is this advantageous? How do the cilia penetrate the fused
ossicles? Examine the spines of Strongylocentrotus. Are they all similar? Why is this so?
Examine how the spines are attached to the surface of the test (skeleton) and examine their
movement (see page 298 of S&S). Locate the tube feet on the urchin and note that they are
restricted to five bands on the test known as the ambulacra. The ambulacra areas are separated
from each other by five interambulacral regions which have no tube feet. It should be easy to
envision the relationship between starfish and urchin after seeing this basic five-part pattern.
Examine locomotion in your urchin and describe the roles of tube feet and spines. Are
there any obvious modifications of tube feet and spines for locomotion purposes? Turn your
urchin upside down and see if it is able to right itself. How is this accomplished? The organs
of equilibrium in most urchins are modified bean-shaped spines known as sphaeridia. They are
generally found on the ambulacral areas around the mouth, but some urchins that live in wave
exposed areas have them along the entire ambulacra. Carefully remove che tube feet at the edge
of the periostome and attempt to remove the sphaeridia. Now test the urchin for a righting
response and see if the surgery has influenced its behavior.
Examine the structure and distribution of the pedicellaria of Strongylocentrotus How many
types of pedicellaria can you find? How do they differ from asteroid pedicellaria? What is
their function? Watch their operation by pulling a piece of hair or thread over the urchin's test.
You can examine their microstructure by removing a couple and placing them in sodium
hypochlorite, and then examining under the compound microscope. See page 298 of S&S.
Sea urchins have become a standard organism for examining fertilization and development
since they are generally cooperative in the laboratory. Like all echinoderms, they are dioecious,
have external fertilization, and generally reproduce seasonally and/or synchronously. Male and
female urchins (only urchins know the difference without a dissection) can be stimulated to
release their gametes by injecting them through the periostome with 0.5 ml of 0.5 M KC1.
These gametes can be artificially fertilized and watched in the laboratory. You will want to start
this part of the laboratory as soon as you arrive. Follow the directions given on pages 300-301
of S&S. Try to observe fertilization and at least one subsequent cleavage. If we are successful,
we can incubate some fertilized eggs and try to observe free-swimming larvae in next week's
Anesthetize your urchin by placing it in 7% MgCl2 for about 30 minutes. Remember to
use only glass containers with chemicals. With a saw or pair of scissors, cut through the equator
of the urchin and separate the two halves as shown on page 281 of S&S. Carefully examine the
internal structures of your urchin using the illustrations in S&S. Chip off a large piece of test
containing both ambulacral and interambulacral regions and boil lt in sodium hypochlorite.
Examine it closely under the dissecting microscope and compare echinoid test structure with the
ossicles of other echinoderms.
Pay particular attention, when examining the internal structures, to the Aristotle's
lantern. The lantern is composed of muscles and calcareous plates and is used in feeding and in
boring into the substrate in some urchins. Its structure is illustrated on page 282 of S&S.
You should also examine a specimen of the sand dollar Echinarachnius. See page 283
of S&S for an illustration. Sand dollars have assumed a bilateral symmetry. They are flattened
in the oral-aboral plane and the anus has shifted to the edge of the test. The ambulacra are
reduced to a petaloid structure on the aboral surface and ambulacral grooves on the aboral
surface and ambulacral grooves on the oral surface. Each ambulacrum contains a double row of
tube feet that run from the petaloid aboral end to the edge of the test. At the aboral end to the
edge of the test. At the aboral end of each ambulacrum is an ocular plate that contains a
light-sensitive podium. Between the ocular plates are four larger genital plates, each bearing a
genital pore and a large madroporite. Are the aboral tube feet locomotory in function? Are the
spines of the aboral and oral surface uniform in size and distribution?
On the oral surface examine the Aristotle's lantern and the arrangement of cilia and spines.
Cut open a preserved sand dollar and examine the structure of the lantern.
Given the arrangment of spines, tube feet, and the habitat of sand dollars, how do you think
GLOSSARY FOR INVERTEBRATE CONFUSION
This glossary, to be used with the 4th edition of "Invertebrate Zoology" by R. D. Barnes (1980,
W. B. Saunders Co.), was compiled as a labor of love to fill what seemed to a former student to
be a considerable gap in the chain of information from text to reader. It makes no pretense to
include every scientific term. Those which are in common use as well as obvious ones, i.e.
circum pharyngeal, dorso- or ventro lateral, were deliberately omitted.
It is hoped that it will clarify or ease the path to the understanding of the vocabulary of
PREFIXES AND SUFFIXES
L., Latin; G., Greek
a, ab (L) away, from
a, an (G) not, without
acanth (G) thorn, spine
actin (G) a ray
ad (L) toward, near
alveol (L) pit
ampho- (G) both, double
ape, apo- (G) away from
archeo- (G) beginning, first in time
athro- (G) joint
bi-, bio- (G) life
blast- (G) bud, sprout
brachi- (G) arm
brachy- (G) short
branchi- (G) fin, feather
bucc- (G) the cheek
calie- (x) (G) cup
capit- (L) head
caud- (L) tait
cephal- (G) head
cerc- (G) tail
ceno- (G) new, recent
chaet- (G) hair
choan- (G) funnel, tube
-chord (G) gut, string
chrom- (G) color
coel- (G) hollow
cten- (G) comb
cutis- (L) skin
cyto- (G) hollow, cell, vessel
de- (L) down, away from
dent- (L) tooth
derm- (G) skin
de-utero- (G) second
di- (G) double, two
duct (L) a leading, conducting
e, ex (L) out, without, from
ect- (G) outside
end- (G) within
enter- (G) bowel
ep(i)- (G) on, upon, over
eu, ev- (G) good, true
-eury (G) broad
fer (G) carrier of
fil (L) thread
gaster (G) belly
glob (L) ball
glom, glomer (L) ball of yarn
gnash (G) jaw
gul (L) throat
gymn (G) naked
gyr (G) round, circle
haem (G) blood
hal (G) the sea
hemi- (G) half
hetero (G) other, different
hist- (G) web, tissue
hal- (G) whole, entire
homo- (G) alike
hypo- (G) under
hyper- (G) above, beyond
in (L) in, into, not, without
is-, iso- (G) similar, equal
lecith- (G) yolk
loph- (G) ridge, crest
lumen (L) light
macr (o) (G) large
mela (G) black
mere (G) a part of
meso (G) middle
mete (G) next to
mio (G) less
micr (o) (G) small
mon (o) (G) one, single
morph (G) shape
neo (G) new, recent
not (o) (G) the back
odont (G) tooth
oligo (G) few
omm (L) all
opercul (L) cover, lid
opisth (G) behind
orth- (G) straight
paleo (G) ancient
par (a) (G) beside
pectinate (L) comb-like, having tooth-like projections
peri (G) around, near
phag (G) to eat
phil (G) loving, friend
phor (G) to bear
phot (G) light
phyl (G) tribe
pinaco (G) board, tablet
platy (G) broad
plio (G) more
pod (G) foot
poly (G) many
poro (G) hole, passage
post (L) after, behind
prim (o) (L) first
pro (G) before, in front of
prove (G) forward, in front
proto (G) early
pseud (o) (G) false
pulmo (G) lung
pyg- (G) rump
ram (L) branch
retro (L) backwards
rhin (G) nose
rhinch (G) beak, snout
sarc (G) flesh
scler (G) hard
som (e) (G) body
squam (G) scale
steg (G) roof
sten (G) narrow, straight
stom (a) (G) mouth
styl (e) (G) pillar, column
sub (L) under, below
super (L) above, over
syn, sym (G) together
tele (G) far
teleo (G) perfect, entire
tetr (G) four
thee (G) case, container
therm (o) (G) heat
trem (G) a hole
tri (G) three
trich (G) hair
trop (G) a change, a turn
troph (G) a feeding, one who feeds
vas (L) vessel
ventr (L) belly
zoe (ie) (G) life
zyg (G) yolk, a coupling, linkage
Acanthocephala(G. akantha, thorn + kephale, head). A phylem of parasitic worm-like pseudo
Acanthor (der. see above). Larval form of above.
Acoelomate (G. a, without + coel, hollow). Animals which lack a body cavity and a solid type of
Acontium (G. Aconto, spear, javelin). In polyps, a mesenterial filament which projects into the
gastrovascular cavity and produces enzymes for digestion of food.
Acron (G. akron, top, summit, peak). The unsegmented head (prostomium) of annelids.
Actinula (G. acting, rod, beam). A larval form of hydroids
Aerobe (G. aero, air + bios, life). An organism which requires air or oxygen for life.
Aesthetes (G. aisthetikos, sensitive, perceptive). In chitons, mantle cells lodged in the tegmentum
which act as sensory organs.
Ambulacral area (L. ambulacrum, walk). Five sections of the oral area of echinoderms which
Ambulacral grove. A furrow extending from the mouth of echinoderms; in a sterodia along each
Amictic (G. a, not + mixtos, mixed). A thin-shelled diploid egg which cannot be fertilized and
develops by parthogenesis into an amictic female.
Amphid (G. amphi, around, double). An inervated invagination of cuticle in nematodes.
Ampulla (L. flask, bottle). Bulb at end of lateral canal in astroida.
Anabiosis (G. + bios, life). Inactivity accompanied by water loss and very low metabolic rate.
Also cryptobiosis (G. Kryptos, hidden, concealed + bios, life).
Anaerobe (G. an, not + bios, life). An organism which cannot exist in the presence of air or
Anastomose (G. anastomosis, new outlet, new network). Connection between two vessels or
Annulus (L. annulus, ring). A spiraled transverse groove of dinoflagelates. If a simple ring, it is
termed a girdle.
Apodeme (G. apo, from, off, away + demas, body). Projection of procuticle of exoskeleton
muscle attachment in crustaceans.
Aposematic (G. apo, from, off, away + sema, sign, token). Warning coloration.
Archenteron (G. archea, beginning, first cause + enteron, intestine). Pouch formed by
invagination of blastula to form primitive gut.
Archeocytes (G. arche, beginning + cyte, cell, hollow place). Phagocytic cells found in the
mesohyl of spongia.
Articular membrane (L. articulus, joint). A thin, chitinous membrane joining segments of the
Ascus (G. asco, bladder, bag). A space under the frontal plate which provides, with muscles, the
means of protruding the lophophore of bryozoans.
Atrium (L. vestibule, hall). The interior cavity of asconoid sponges.
Autogamy (G. autos, self + gamete, husband, wife). Self mixing of genetic material within the
Autotomy (G. autos, self + temno, cut). The act of casting off an appendage.
Autozooid (G. autos, self + zoe, life). An individual feeding bryozoan.
Avicularium (ia, pl.) (G. avis, bind). A heterozoid in the form of a pincers or jaw which serve to
protect the organism.
Basopodite (G. basis, pedistal, foundation + pod, foot). A/crustacean appendage process attached
to the coxapodite and which bears the endo- and exopodites.
Bdelloid (G. bdelo, leech + oid, like, having the appearance of).A class of fresh water rotifers.
Benthic (G. benthos, deep). Bottom dwelling organisms.
Biramous (L. bi, two + ramus, branch). Two branched; Sometimes extended to cover more than
Blastula (G. blastos, germ, bud, sprout). The early developmental stage of a metazoan; a
spherical layer of cells enclosing a central cavity.
Blastomere (G. blastos, germ, bud, sprout + mere. a part). A cell produced during cleavage of an
ovum; a blastula cell.
Blastozoid (G. blastos, germ, bud, sprout + zoe, life). A reproductive bud of tunicates.
Book gills. Leaf like lamellae of Limulus which serve as organs of gaseous exchange i.e. gills.
Brachiole (G. brachion, arm). A slender pinnule-like projection which contains the peripheral end
of the food groove of fossil crinoids.
Buccal (L. bucca, cheek, cavity). A cavity just within the mouth opening .
Budding - See fission.
Calyx (G. Kalyx, cup, cover). The body, as differentiated from the stalk, of an ectoproct; the
skeletal cup within which a polyp is fixed (scleractinian corals).
Capitulum (L. capitalis, relating to the head). In stalked Cirripedia, the main body, excluding the
Carapace (Sp. carapach(o), shield). A chitinous exterior structure covering the crustacean thorax
minimally and sometimes the whole body.
Cecum, caecum (L. caecum, blind). A pouch or sac within the body which has only one opening.
Centrolecithal (G. Kentron, mid point + lecitho, yolk). An ovum in which the nucleus is
surrounded by a small amount of nonyolk cytoplasm within a large yolk mass.
Cephalon (G. cephalo, head). The interior body of trilobites.
Cerata (G. Keratos, horn). Dorsal body projections of nudibranchs.
Cercaria (New Latin). The fourth developmental stage of trematodes i.e. a free-swimming tailed
Chelicerae (G. chele, claw) . Claw-like feeding appendages of chelicerates (eg. horseshoe crabs).
Coanocyte (G. coane, funnel + cyto, cell). Spongia cells which are flagellated and collared which
create water currents and extract food from them.
Chloragogen (G. ehlor, green + agogue, stimulating). A substance in cells which serves as a
center for glycogen and fat synthesis in oligochaetes.
Chromatophores (G. chrom, color + phore, bearer). Pigment cells in cephalopods.
Cilium, pl. cilia (L. eyelash, hair). A hair-like projection of the cell wall used for locomotion or
Cirri (L. cirrus, curl, tendril)
1. In crinoids, small, jointed appendages attached of the stalk.
2. In Cirripedia, thoracic feeding appendages.
3. In Ciliata, ciliary tufts used for locomotion.
4. In polychaetes, a sensory appendage.
5 . In trematodes and neohabdocoels, an eversible copulatory organ.
Clavules (L. clavus, nail). Specialized spines of Echinoideae. They are believed to produce
mucus for burrow maintenance and to create water currents.
Clitellum (L. clitella, pack saddle). A glandular segment of oligochaetes and hirudinates which
forms a reproductive cocoon.
Cnidosac (G. Knide, nettle + sakkos, bag). Structures at the tip of cerata of nudibranchs which
Cnidocil (G. Knide, nettle + cdl, deriv. unknown). A short bristle-like process on the end of the
cnidocyte which triggers the discharge of nematocysts.
Cnidocyte (G. Knide, nettle + cytos, cell). Cells which contain stinging structures (nematocysts).
Coanenchyme (G. coeno, common + chymos, juice). In octocorallians, a mass of mesoglea which
has gastrodermal tubes connected to adjacent polyps.
Colloblasts (G. collo, glue + blastos, ball). In ctenophores, cells which have adhesive properties
and which are analagous to nematocysts.
Columella (L. dim. columella, pillar). Central column of the shell of gastropods.
Commissure (L. committere, to bring together). A band of fibers joining symmetrical parts,
especially in the brain.
Condyle (L. condylus, knuckle, knob, enlarged end of a bone). A cuticular knob which engages a
socket and permits movement between body segments of arthropods.
Conjugant (L. con, with + jugum, yoke, pair). Fused ciliates.
Contractile vacuole. Water balancing organelle.
Coracidium (G. Korak raven, deriv?)1. Early larval stage of turbullarians. 2. Also an
Coxa (L. hip). The basal section of the leg of chilicerates and insects.
Coxal gland (L. coxa, hip). Thin walled sacs which serve as excretory organs of chilicerates.
Coxapodite (L. coxa, hip + G. pod, foot). The crustacean appendage process nearest the body, to
which the basopodite is attached.
Crown (L. crone, crown, wreath). The pentamerous body of a crinoid.
Cyclomorphosis (G. cyclo, circle + Morpho, shape, form). A seasonal change in body shape or
Cyclosis (G. cyclo, circle). Streaming protoplasm in amoba.
Cysticercus (G. cyst), bladder + New Latin, cercaria, tadpolelike). The second stage of
development of cestodes; pre-adult stage.
Cytoplasm (G. cyto, cell + plasma, substance). The material contained within the cell wall.
Cytostome (G. cyto, cell + stom, mouth). Mouth or oral chamber of ciliates.
Cytopyge (G. cyto, cell + pygo, rump, buttocks). Anal opening in ciliates.
Dactylozooid (G. dactylo, finger + zoe, life). Specialized defensive polyp in hydrozoans.
Demibranch (L. dimidius, half + branchos, gill). One of a pair of lamelli branch gills.
Deutocerebrum (G. deutos - double + L. cerebrum, brain). The median region of the brain of
Digenea (G. di, twice, two + genesis, birth, origin). A parasitic organism whose life cycle
involves two or more hosts.
Dioecious (G. di, twice, two + oeco, house). An organism which produces either male or female
gametes, but not both.
Ditaxic (G. di, twice, two + tasso, place arrange). A fine muscular contraction which sweeps
across half of the foot of some molluses (gastropods).
Diverticula (L. diverticulum, a by-path). In anatomy, a pouch or sac opening out from a tube or
Dorsal lamina (L. dorsum, back + lamina, plate). A projecting ridge of finger-like processes
(languets) which run from the pharynx to the esophagus in tunicates.
Ecdysis (G. ekdysis, escape, molt). The shedding of arthropod skeleton.
Ecdisone (G. ekdysis, escape, molt). Hormone which causes ecdysis.
Echinoplutens (G. echinos, sea urchin + L. pluteus, shield, parapet). The second and planktonic
larral stage of echinoderms.
Elytra (G. elytron, shield, husk). Plate-like scales.
Ectoplasm (G. ecto, out of + plasm, substance). Outer portion of cytoplasm of cells.
Endoplasm (G. endo, within + plasm, substance). Inner portion of cytoplasm of cells.
Endopodite (G. endo, within + pod, foot). Appendage process which is attached to basopodite of
Endostyle (G. endo, within + stylos, pillar, column). In tunicates, a deep groove which extends
the length of the pharyngeal wall which contains mucus secreting cells and flagellae.
Entolicithal (G. ento, within + licitho, yolk). An ovum which has the yolk as an integral part of
Entoproct (G. ento, within + proktos, anus, rectus, tail). Sessile bryozoan-like animals with the
mouth and anus within the tentacular crown.
Ephyrae (Deriv. unknown). Immature medusae.
Epiboly (G. epibole, to place upon, throw). In histology, overriding or surrounding other cells in
Epicardium (G. epi, on, over, upon + Kardia, heart). In tunicates, a tube which parallels the
Epicuticle (G. epi, on over, upon + L. cutis, skin). The exterior portion of the chitinous arthropod
Epiphytic (G. epi, on, over, upon + phytos, plant). Concerning plants which grow
non-parasitically on others.
Epipodite (G. epi, on, over, upon + pod, foot). Appendange process which is attached to, or is
apart of, the coxapodite of crustaceans. It frequently bears gills.
Epistome (G. epi, on, upon, over + stome, mouth). A narrow crescent fold which overhangs the
mouth of phoronids.
Epitheliomuscular cells (G. epi, on, over, upon + there, nipple; + L. musculus, flesh). In hydra,
epithelial cells which have basal extensions connected to each other and which are contractile.
Epitoke (G. epi, on, over, upon + toco, birth, offspring). An annelid reproductive individual
adapted for bottom dwelling or pelagic existence.
Epitoky (See above). The formation of an epitoke.
Epizoic (G. epi, on, upon, over + zoon, animal). An external parasitic form.
Esthetases (G. aisthetikos, sensitive, perceptive). Chemoreceptors on the first antennae of
Eukaryote (G. eu, good, well + caryo, nut, kernel). A cell whose nucleus is enclosed within a
membrane, a characteristic of all life above the level of bacteria and blue-green algae.
Eumellibranch gill (G. eu, good, well + L. lamina, plate + G. branchos, gill, fin). Molluscan gills
which have formed solid sheets of tissue.
Eutely (G. euteleia, thrift, economy). A condition of some aschelminths in which the body is
made up of a constant number of cells for each species.
Exopodite (G. exoterikos, external + pod, foot). An appendage process which is attached
externally to the basopodite of crustaceans.
Exumbrella (L. ex, out of + umbra, shace). The exterior upper surface of a medusa.
Facultative (L. facultas, feasibility, means). Having the ability to live under more than one
environmental condition i.e. parasitic or non-parasitic.
Fillibranch gills (I.. filix, fern + G. brachos, gill, fin). Molluskan gills in which the individual
filaments are more or less separate.
Filopodia (L. glum, thread + G. pod, podium. foot). A pointed pseudo-podium.
Fission (L. cleft, chink). Formation of daughter cells by division:
a. Binary if result is two similar cells
b. Budding if result is two dissimilar cells
c. Schizogony if result is multiple division
Flabellum (L. fan). Spatulate process on last leg of Limulus used to clean gills.
Flagella (L. flagellum, small whip, lash). A long slender motile appendage of cells.
Funiculus (L. funds, rope, cord). Tissue which connects individual bryozoans through pores and
which provides some sort of communication .
Flame cell. The protonephridium of turbellarians. See text (Barnes, pages 220, 221 and 222).
Gametamy (G. gametos, wife, husband, spouse). Sexual reproduction
Gametogonia (G. gametos, spouse + gone, seed). Primary gametodytes which are shed into the
coelom of polychaetes.
Gamete (G. gametos, spouse). Reproductive cell.
Gamont (G. gamos, union). A gametocyte which is the precursor to a gamete. (See gamogony).
Gamogony (G. gametos, spouse + gonad, seed). The development of gametes.
Ganglion (G) A knot or plexus of nerves.
Gastrodermis (G. gastro, stomach + derma, skin). Nutritive muscle cells of cnidarians and
Gastrovascular cavity (G. gastro, stomach + vas, vessel, pouch). A space or channel for digestion.
Gastrozoid (G. gastro, stomach + zoid, life-like). Hydrozoan feeding polyp; food gathering
individual in colonial tunicates (trophozoite).
Gastrula (G. gastro, stomach). A cup-like early stage of germ layer formation characterized by
two layers of cells.
Gemmules (G. gemma, bud, eye). A spore-like aggregate of sponge material which winters over
and grows into a larva in the spring.
Girdle (Anglo-Saxon, gydrdel, belt). In polyplacophorans, the peripheral area of the mantle.
Gonophore (G. gone, seed + phore, bearer, carrier). The repro ductive structure of a polyp (See
Gnathobase (G. gnathos, jaw + basis, foundation). Heavily armed processes at base of
appendages for grinding food in Limulus.
Gnathopods (G. gnathos, jaw + pod, foot). The 2nd and 3rd appendages of amphipods which are
modified for prehension.
Hectocotylus (G. hecto, hold + Koides, hollow). A cephalopod arm modified as a reproductive
Hemocoel (G. haima, blood + coelo, cavity, cup). In arthropods, a sinus or space filled with
Hemocyanin (G. haima, blood + cyano, dark blue). The oxygen carrying component of the blood
of arthropods, cephalopods, crustaceans and mollusks.
Heterozoid (G. heteros, other, different + zoe, life). A modified bryozoan individual which serves
many different functions i.e. stolous, attachment discs, etc.
Hologamy (G. holo, entire + gamos, union). Fusion of two individuals, each acting as a gamete.
Holophyte (G. holo, entire + phyto, plant). The form of life able to create nutriments out of water,
minerals and lignt.
Holozoic (G. holo,entire + zoon, animal).
Homologous (G. homologos, agreeing). Corresponding in type of structure and deriving from a
common primitive origin.
Homology - The state of being homologous.
Hydranth (G. hydra, many headed + anthus, flower). The oral end of a polyp.
Hydrocaulus (G. hydra, many headed + L. caulis, stalk). The stalk of a polyp.
Hydrotheca (G. hydra, many headed + theca, case, container). The continuation of the perisarc of
hydroids which encloses the hydranth
Hydrorhiza (G. hydra, many headed + rhizo, root). Root-like structure at the base of a polyp.
Hypertrophy (G. hyper, very, above + trophe, food, growth). Excessive growth.
Hypertonic (G. hyper, very, above + tongs, stretching). A medium with high osmotic pressure.
Hypodermis (G. hypo, under, beneath + cerma, skin). In arthropods, the underlying layer of
integumentary epithelial cells.
Hypostome (G. hypo, under, beneath + stoma, mouth). The mouth of a hydra.
Hypotonic (G. hypo, less than, under, beneath + tongs, stretching). A medium with low osmotic
Instar (L. form, likeness). Stages between growth periods in arthropods.
Intralecithial (L. intra, within + G. lecitho, yolk). Superficial cleavage of arthropod eggs.
Interstitial (L. interstitium, interstice). Situated between the cellular components of tissue;
specifically between the epidermis and epithelio-muscular cells of hydras.
Introvert (L. intra, within + versus, turn). The head and anterior part of the body of
pogonophorans which can be retracte into the body.
Iridocycle (G. irid, rainbow, iris + Kylon, area under the eye). Cells in the chromatophores of
cephalopods which reflect light differentially.
Isogamy (G. iso, the same + gamete, spouse). The fusion of two gametes with the identical
Isomyarian (G. iso, the same + L. mya, a kind of mussel). A primitive lamellibranch in which the
adductor muscles are more or less equal.
Kinetosome (G. Kinetico, pertaining to motion + some, body). Organelle to which the base of the
cilium or flagellum is attached.
Labial palp (L. labium, lip + G. palpo, touch, feel). Flap-like folds associated with proboseides
which act as food sorting stru tures.
Labium (L. lip). The lower lip of arthropods.
Labrum (L. lip). The lip-like upper prominence of mouth parts of chewing insects.
Lamellibranchea (L. lamella, plate + G. branchos, lung). See pelecypod.
Lappets (Mid. Eng. lappe, fold, wrap). Movable plates on ambulacral groove of crinoids, each
associated with three podia.
Lamellibranchea (L. lamina, plate + G. branchos, gill, fin). Mollusks having 2 valves hinged
dorsally and with sheet-like gills having a food gathering function. Symon. bivalves, pelecypods.
Lamella (L. lamina, plate).
a. Folded filament half of molluskan gill
b. Leaf-like folds of gills of chelicerates (book gills).
Lanquets (Deriv. unknown). Finger-like processes which run posteriorly to the esophogus of
Lecithotrophic (G. lee, tho, yolk + trophe, food, nourishment). Developing forms which receive
their nourishment from yolk.
Lobopodia (G. lobos, a rounded protuberance + pod, foot). A blunt pseudopodium.
Locular (L. loculus, cell, box). A chambered body.
Lophophore (G. lopho, mane, crest + phore, bearer, carrier). A food capturing organ consisting of
ciliated tentacles which are found on phoronids, bryozoans and brachiopods.
Lorica (L. lether cuirass or corselet). The shell, test or thickened encasement of bdelloid rotifers.
Lumen (L. light, window). In biology, a duct, hollow or enclosed space.
Lunules (L. dim. of luna, moon or crescent). Large elongated notches or openings in the body of
Lysosome (G. Blysis, dissolve, break up + some, body). A cellular organelle containing digestive
Madreporite (Deriv. unknown - perhans Spanish madre, mother + G. poros, hole). A modified
pore V in the aboral surface of some echinoderms. [which connects to water channels.]
Malpighian tubules (Malpighi, Italian anatomist who discovered capillaries + L. tubus, pipe).
Slender tubes which carry wastes from the diverticula to the intestine.
Mandible (L. mandibula, jaw). Short, heavy mouth parts of crustaceans used for biting and
a. In bivalves and brachio pods, a sheet of muscular, sensory and secreting tissue lying
beneath the valves.
b. In cephalopods a muscular structure surrounding the body. c. In barnacles, the
enveloping carapace of larval forms.
Manubrium (L. handle, haft). A scyphoran structure which hangs from the subumbrella and
surrounds the mouth aiding in capture and ingestion of prey.
Marsupium (G. marsupion, pouch, bag). In amphipods a brood chamber which holds the eggs.
Mastax (G. mouth). The mouth of a rotifer.
Mastigophora (G. mastigo, whip + phore, bearer, carrier). Zoo or phytoflagellales which have
Maxillae (L. jawbones). Pairs of feeding appendages of crustaceans.
Maxillipeds (L. jawbone + G. pod, foot). The first three appendages on the thorax of
malacostrans which have been modified to manipulate food.
Medusa (L. a gorgon). A free swimming bell or umbrella shaped cnidarian.
Medusoid (L. a gorgon). In hydra, a free swimming reproductive form which develops into a
medusa or is retained as a gonophore.
Mesenchyme (G. meso, middle + chymos, juice). Cells which develop into connective tissue,
blood and blood vessels.
Mesenteron (G. meso, middle + enteron,- intestine). The central part of anthozoan gastrovascular
Mesentery (G. meso, middle + enteron, intestine). A supporting or enfolding membrane which
attaches organs to the body wall or other organs.
Mesoglea (G. meso, middle, glia, glue). The thick gelatinous material making up the major part
of the inner body of medusae.
Mesohyl (G. meso, middle + hylister (?), sieve). A gelatinous matrix lying below the pinacoderm
Metachronal (G. meta, between, after + chronos, time). Wave-like beating of fields of cilia or
Metamerism (G. meta, between, implying change + meris, share portion -pernaps indicating
change from acoelomate to coelomate body archetecture). Division of body into segments along
an amteropostorior axis.
Metanephridium (G. meta, between + nephro, kidney). The nephridium in which the preseptal
end is an open ciliated funnel.
Metazoan (G. meta, between + zoon, animal). A multicellular motile heterophic animal.
Mictic egg (G. mictos, mixed). A haploid egg which produces males parthogenically if not
fertilized. If fertilized, they become dormant after which they develop into females.
Monoecious (G. mono, single + oeco, house).- An individual which produces male and female
Monogenea (G. mono, single + genesis, birth, origin). A parasitic organism having only one form
or generation in the life cycle.
Monoplacophora (G. mono, single + placo, tablet + Phore, bearer, carrier). A class of mollusks
having a single symmetrical shell.
Monopodal growth (G. mono, single + pod, foot). In hydrozoans, growth at the distal end of the
stalk with lateral branching of secondary polyps. The oldest polyp and its hydranth occupy the
Monotaxic (G. mono, single + tasso, arrange, place). A fine muscular contraction which sweeps
synchronously across the whole surface of the foot of gastropods.
Myogenic (G. myo, muscle + genesis, birth, origin). Muscle contraction which originates and is
controlled within the muscle itself.
Myonemes (G. myo, muscle + nema, thread). Long contractile fibrils in ciliates.
Nauplius larva (Der. unknown). Earliest larval form of crustaceans - basic crustacean type.
Nematocyst (G. nemato, thread + cystos, cell). Toxic stinging structures carried by cnidocysts in
hydrozoans and scaphozoans.
Nephridium (G. nephro, kidney+ L.ium,quality or nature of). A tubule specialized for excretion
and/or osmoregulation. See proto- and metanephridia.
Nephrocytes (G. nephro, kidney + cytos, cell). Cells which are capable of filtering and
accumulating waste particles.
Nephrostome (G. nephro, kidney + stoma, mouth). The fan shaped open and ciliated end of
metanephridia in polychaetes.
Neuro pile (G. neuron, nerve + L. pile, column). Intertwined processes of the interior of the
Neuropodium (G. neuro, nerve + pod, foot+ L. ium,quality of). Lower part of the parapodium.
Nudimental gland (L. nudus, nest). A gland of cephalopods (e.g. Loligo) which provides a
gelatinous mass which covers the eggs.
Notopodium (G. noto, back + pod, foot). The upper part of the parapodium.
Nucal organs (Arabic, nukla, nape of neck). Ciliated sensory pits in the head region of
Nucleus (L. nucula, dim, kernel). Chromosomes contained within a double membrane, separate
from the cytoplasm of the cell. The region of the cell containing the genetic material, separated
from the cytoplasm by a double membrane (the nuclear envelope).
Nudibranchs (L. nudus, bare + G. branchos, gill, fin). An order of gastropods characterized by a
secondarily bilateral symmetry and loss of shell, mantle and original gill.
*They are coiled tubes with a short, stiff bristle-like process which is everted for protection or
Obligate (L. obligatus, bound) Biol. Restricted to a particular condition of life i.e. parasites which
must live in close association with hosts.
Odontophore (G. odonto, tooth + phore, carrier, bearer). The cartilaginous base for the radula of
Onchosphere (G. oncho, hook, barb + L. sphere, ball). The ciliated free-swimming larva of
Operculum (L. cover, lid). In serpulids, a modified radiole which serves as a plug when the
crown is withdrawn.
Ophiopluteus (G. ophio, snake + L. pluteus, shed, parapet). The second and planktonic larval
stage of ophioroides.
Opisthaptor (G. opistho, behind + apo, bind, fit). A muscular organ which attaches a parasite to
its host by means of suckers, hooks, etc.
Opisthosoma (G. opistho, behind + some, body). The posterior portion of pogonophores.
Osculum (L. little mouth). The large opening at the top of the atrium of asconid sponges.
Osphradium (G. osphresis, smellable). Sensory areas on the poster margin of efferent gill
membranes which have a chemoreceptor function.
Ossicle (L. ossiculum, dim. of ossis, bone). Calcareous rods, crosses or plates which are the
skeleton of asteroids.
Ostium, Ostia, pl. (L. door). Lateral openings in the heart of arthropods. Also the incurrent pore
Ovicell (L. ovum, egg + cell). A structure at one end of bryozoans which holds the embryo and
serves as a brooding chamber.
Ocelli (L. ocellatus, having small eye spots). Light sensitive organs.
Ommatidium (G. omma, eye + unknown deriv.). A long cylindrical structure possessing the
ability of light reception in the arthropod eye.
Oxconformers (G. oxys, sour, acid + E. conform, to adapt). Organisms whose oxygen
consumption is regulated in part by the amount available.
Paedogenesis (G. paedo, child + genesis, birth, origin). A sexually mature larval form which does
not become adult.
Paedomorphosis (G. paedo, child + morph, form + osis, condition of). Reaching sexual maturity
with juvenile morphology. In an evolutionary sense.
Palium (L. mantle, robe). The epidermis underlying the shell of mollusks.
Palium sinus (L. mantle, robe + sinus, space, hollow). A hollow structure below the adductor
which is the point of attachment of the siphon of mollusks.
Palruella (Deriv. unknown). A stage of development in flagellates characterized by loss of the
flagellum and non-motility.
Papula (L. pistule, pimple). Outpockets of epithelium of echinoderms which serve, with tube
feet, as gas exchange surfaces.
Parapodium (G. pare, beside, near + pod, foot). Lateral appendages extending from the segments
of annelids and from the body or foot of some mollusks.
Parenchyma (G. pare, beside, near + chyma, juice). A spongy mass of cells.
Parthenogenesis (G. parthenos, virgin + genesis, birth, origin). Reproduction by the development
of an unfertilized egg.
Paxilla (L. paxillus, nail, peg). Ossicles on the aboral surface of asteroids raised above the
surface and crowned with small spines.
Pecten (L. comb). Comb like chitinous plates which project from the sides of scorpions and
which are sensory.
Pedicellariae (L. pes, pedis, foot + cellarius, steward). Small specialized jaw like structures of
echinoyds which protect, and in one case, capture prey.
Pedicle (G. pea, foot + L. iculus, dim. suffix). A cylindrical extension of the ventral wall of
orachiopods which attaches to the substrate.
Pedipalp (L. pes, pedis, foot ~ palpo, feel, touch). A sensory appendage arising out of prosoma
and modified to perform various functions.
Pelecypod (lamellibranch) (G. pelecy, ax, hatchet + pod, foot). A class of mollusks which have
two shell valves and a large foot, both laterally compressed, and gills which have assumed a food
Pelmatazoa (G. pelma, sole of foot). Animals which travel on soles of foot (i.e. gastropods).
Pellicle (L. pellis, skin). Body covering of ciliates.
Pericardial (G. pert, near, on, around + kardia, heart). The region nearest the heart.
Perihemal - spaces or sinuses (G. pert, on, around, near + hema, blood). Separate extensions of
the coelam; part of the bloodvascular system of asteroides.
Perrostracum (G. pert, on, around, near + ostrakon, shell). The outer layer of the mollusk shell.
Peripods (G. peri, on, around, near +pod, foot). Crustacean thoracic appendages.
Periproct (G. pert, on, around, near + proctos, anus). The anal region of echinoderms.
Perisark (G. pert, on, around, near + sarco, flesh). In hydroids a non-living protein-chitinous
envelope which acts as a support.
Peristalsis (G. pert, on, around, near + staltikos, contraction). Undulations produced by waves of
contraction in the longitudinal muscles of the body wall.
Peristome (G. pert, on, around, near + stoma, mouth)
1. Groove which leads to cytostome in protozoans
2. Pre-oral chamber of ciliate
3. First complete segment of annelids
4. Post-oral region of polychaetes.
Peristomial membrane (G. pert, on, around, near + stoma, mouth). In ophiuroids a roof-like
structure over the prebuccal cavity.
Perivisceral (G. pert, on, over, around + L. viscera, entrails). Region nearest the intestines.
Petaloid (G. petalon, leaf). In echinoderms the aboral ambulacural area which radiates from the
Phagocyte (G. phago, to eat + cyte, hollow place, cell). Cells which engulf food particles or
foreign bodies. (Phagocytosis; the process of engulfment by a phagocyle)
Phasic neurons (G. phasis, to appear + neuron, nerve). Newrons which initiate fast but brief
muscle contractions in arthropods.
Pharynx (G. throat). Area between the mouth and nasal passages and the larynx.
Phasmid (G. phasma, apparition, specter). Unicellular glands in the tail of nematodes.
Phytoflagellate (G. phyto, plant + L. flagellum, whip). Single celled protozoa having flagellae
Photophores (G. photo, light + phore, bearer). Light producing organs of euphaniaceans-krill.
Pinnules (L. pinnula (dim.), feather, wing). Jointed appendages on arms of crinoids giving them a
Pinocytosis (G. ping, drink + cyto, cell). Uptake of liquid by cellular engulfment.
Polyplacophore (G. poly, many + placo, flat, tablet + phore, bearer, carrier). Chitons which have
eight overlapping transverse plates as shells.
Plankton (G. planeto, wandering, roaming). Floating oceanic organisms.
Planospiral (L. planus, flat, even + spiralis, coil, twist). A spiral form which extends more or less
Planula (L. planus, flat, even). Ciliated free swimming larva of coelenteratis.
Pleopod (G. pleo, swim, sail + pod, foot). Interior abdominal appendages used for swimming,
ventilation, food/gathering, etc. in malacostricans.
Plicate gill (L. plicatus, folded). A molluscan gill which the surface of the lamellae has been
increased by folding along the long axis.
Pleuron (G. pleura, side). The two lateral cuticular sections of the skeleton of arthropods.
Podium (L. platform, projection). Tubular projections on the ambulacural groove of asteroids
which serve as locomotor organs.
Polyp (G. polypous, coral). A sessile cnidarian.
Polypoid (G. polypous, coral + eidos, having the form of). Resembling a polyp, a sessile
Pneumostome (G. pneumo, wind, air, breath + stoma, mouth). Porelike opening in pulmonate
snails leading into lung or mantle cavity.
Podium (podia, pi.) (G. pod, foot). Tubular projections on the arms of echinoderms which serve
as locomotor organs.
Polian vessicles (Deriv. unknown). Elongated muscular sacs suspended in the coelom of some
asteroids which are believed to serve as expansion chambers of the water vascular system.
Polychaete (G. poly, many + chaeto, long hair, mane). A class of annelids with paired lateral
fleshy appendages (parapodia).
Polyp (G. polypos, many footed). Coelanterate individual e.g. coral, anemone.
Polyplucophora (G. poly, many + placo, tablet + phores, body). A class of mollusks having a
body covering of transverse overlapping plates.
Polyploid (G. poly, many + ploid - der. unknown). Having more than two complete sets of
Post larva (L. post, after). The last stage in the development of crustacean larvae.
Pre-epodite (L. pre, before + G. epi, around, on, near + pod, foot). Outer gill bearing structure of
the appendage of trilobites.
Proboscis (G,. proboskis, snout). An extensible or extended structure containing sense organs or
mouth and feeding aparatus.
Proboscides (G. pro, in front of + boske, food, fodder). Tentacles on the margin of the mouth of
Proctodeal (G. proctos, anus, tail). The hind gut region of arthropods.
Protocuticle (G. pro, in front of + L. cutis, skin). The layer of cuticle lying immediately under the
epicuticle in arthropods.
Proglottid (G. pro, in front of + glottis, mouth of the windpipe). Linearly arranged individual
reproductive segments of the strobila of cestodes.
Prokaryote (G. pro, in front of + caryo, kernel, nut). A one celled organism whose genetic
material is distributed throughout the cell. Includes bacteria and blue-green algae.
Propodium (G. pro, in front of + pod, foot). The fore part of a podium.
Prosobranch (G. prove, forward + branchos, gill). Primitive mollusks of the sub order
Prosoplyle (G. prove, forward + pyre, gate, orifice). Pores opening into the incurrent canals of
Protocereberum (G. proto, first + L. cerebrum, brain). The anterior portion of the brain of
arthropods - see prefixes deutero - and trito.
Protonephridium (G. proto, first + nephro, kidney). Primitive excretory and osmoregulatory
organ. See text (Barnes) for flame cells.
Protoplasm (G. proto, first + plasma, substance, that which is formed). All cellular material.
Protopodite (G. proto, first + pod, foot). The two most proximate elements of the crustacean
Protostyle (G. proto, first + style, pillar, colemn). A rotating mass of mucus in the stomach of
Prototroch (G. proto, first + trocho, ball, round). Free swimming larvae of mollusks characterized
by a girdle of ciliated cells.
Protozoan (G. proto, first + zoon, animal). A single celled animal.
Pseudo branch (G. pseudo, false + branchos, gill). In aquatic pulmonates a gill formed
secondarily from folds of the mantle.
Pseudofeces (G. pseudo, false + L. feces, dregs, rejected material). Material too large to be
digested and egested by bivalves.
Pseudopodia (G. pseudo, false + pod, foot). A flowing extension of the body of sarcodinians.
Pteropods (G. ptero, feather, wing + pod, foot). An order of swimming pelagic opisthobranchs.
Pygidium (G. pygo, rump, tail). The terminal end of annelid worms.
Radioles (L. radium, rod, spike). A bipinnate feeding organ of fanworms which forms a conduit
for transporting food particles to the mouth.
Radule (L. radula, scraper). In mollusks, a feeding organ consisting of rows of chitinous teeth.
Redia (Deriv. unknown). The third developmental stage in the trematode life-cycle.
Rhabdites (G. rhabdo, stick, rod + ite, having the nature of). In turbellarians, rod shaped
Rhabdomere (G. rhabdo, stick, rod + mere, part, portion). The area of retinular cells oriented at
right angles to the axis of the omatidium of arthropods.
Reticupodia (L. reticulatus, net-like + pod, foot). Branched interconnected thread-like
Retinula (L. rete, net). A network of rhabdomes which line the omatidium of arthropods.
Rhabdome (G. rhabdos, rod, staff). An enclosed central space, lined with rhabdomeres, in the eye
Rhmophore (G. rhino, nose + phore, bearer, carrier). Modified opisthobranch tentacle containing
tactile and chemoreceptor cells.
Rhopalium (G. rhopalon, club). Concentrations of neurons in the margins of scyphozoans.
Saccules (L. sacculus, dim of saccus, bag). Small spherical bodies near the outer sides of lappets
Saprophyte (G. sapro, rotten + phyto, plant). A plant which obtains its nutrients from dead
Saprozoic (G. sapro, rotten + zoon, life). An organism which obtains its nutrients from dead
Sarcodinas (G. sarco, flesh). Protozoans having flowing extensions of the body i.e. pseudo podia.
Scalid (L. scale, stair, ladder). Longitudinal rib like conical projections on the introvert of
Schizogamy (G. schistos, split + gamos, union). See fission.
Scolex (G. scolo, thorn, pointed). The anterior region of the head of cestodes.
Scaphognathite (G. scapho, trough, hollow vessel + gnathos, jaw). A paddle-like structure which
produces an inhalent current which flows over the lamellae of malacostrians.
Scyphistome (G. scyphus, cup + stoma, mouth). In schyphozoans, the polyploid larva, similar in
appearance to a hydra, which develops from a planula.
Scyphozoan (G. scyphus, cup). The cnidarians in which the medusa is the dominant and
conspicious individual in the life cycle.
Seminal vessicle (L. semen, seed). A coelomic pouch which provides for maturation of gametes
Septibranch (L. septum, fence, wall + G. branchos, gill). A subclass of mollusks having
degenerate gills modified to muscular septa.
Seta, pl. setae (L. seta, bristle). A modified ennervated cilium.
Sinus (L. cavity, recess). Any cavity, recess, or passage in tissue or bone.
Siphonoglyph (G. syphon, pipe, tube + glypho, carve, engrave). In anemones, a ciliated groove at
each end of the mouth which provides for circulation of water.
Solenogaster (G. soleno, a pipe + gaster, stomach). A class of worms-shaped mollusks.
Spermatheca (G. spermation, seed + theca, case, container). Chambers or receptacles for storage
Spermatophore (G. spermation, seed + phore, carrier, bearer) Sperm contained within a
membrane or case.
Spheridia (L. sphere, ball). Statocyst containing structures in echinoids (urchins, sand dollars).
Spicule (L. kernel of grain, point). Skeletal process of spongia,either calcareous or siliceous.
Sporocyst (G. spore, seed + cyst, cell). The second developmental phase of a trematode
life-cycle, a hollow structure which develops into a radia.
Sporogony (G. spore, seed + gony, node). The development of spores
Sporozoite (New L. spore, seed + zoa, life). Stage in life-cycle of some protozoans, the
development of which follows sporogony.
Statoblast (G. statos, fixed, placed + blastos, ball). Resistant reproductive bodies of bryozoans
which germinate under favorable conditions.
Statocyst (G. statos, fixed, placed + cyst, cell). Kinetic sense organs; chambers containing
statoliths (concretions) in contact with recptor cells.
Sternum (G. sternon, breast, chest). The ventral cuticular skeleton of arthropods.
Sterogastrula (G. stereos, solid, first, hard + gaster, belly, paunch, womb). A blastula changed to
a solid gastrula by ingression, a process by which cells move into the blastocoel.
Stigmata (G. stigma, mark, spot). Pharyngeal slits in tunicates.
Stolon (L. stolo, branch, shoot, runner) - Runner connecting hydroids in colonial cnidarians.
Stomodeal (G. stoma, mouth). The foregut region of arthropods.
Stomodium (G. stoma, mouth + ium). Mouth area of larvae and gastrulae.
Strobila (G. strobilos, twisted or turning). 1. Posterior body of cestodes consisting of linearly
arranged proglettids. 2. The polyploid stage of scyhozoans which produce medusae by transverse
Style sac (G. style, pillar, column). The posterior conical section of the stomach of molluscs.
Subumbrella (L. sub, under + umbra, shade). Lower exterior surface of medusae.
Superposition image (L. super, over f positus, placed, put). The response of a rhabdomere to light
entering from adjacent ones.
Synapse (G. synapsia, connection, junction). Connections between neurons.
Torsion (Mid. Eng. torcion, to twist). In mollusks, the visceral mass, mantle and mantle cavity
being twisted 180degrees counterclock wise.
Totipotent (L. totus, all + noteus, powerful). Cells which can be transformed into all other types
i.e. archeocytes. (Undifferentiated cells)
Trachea (L. windpipe). Respiratory tubes of insects and some arachnids.
Trichobothria (G. tricho, hair + bothros, trench, pit). Long sensitive hairs, set in a socket; the
most important sense organs of arachnids.
Trichocyst (G. tricho, hair + cyst, cell). Organelles containing fluid hardens into rod-like
structures for defense or attachment.
Tritocerebrum (G. tritos, third + L. brain). The posterior region of the arthropod brain
Trivium (L. tri, three + rivus, alive). The three ventral ambulacral areas of holothuroids.
Trophozooid (G. trephin, nourish + zoe, life). A feeding or nutritive polyp (gastrozooid).
Tun (L. tunica, garment, husk). An animal which has undergone anabiosis.
Tunicin (L. tunica, garment, husk). A type of cellulose which is the principal constituent of the
covering of tunicates.
Umbo (L. boss, knob). A dorsal projection of the valve of bivalves.
Vacuole (L. vacuus, em~ty). A liquid-filled cavity in a cell.
Vector tissue (L. carrier, messenger). Special tissue which acts as a passageway for sperm
moving to ovisacs in hirudineans.
Vibraculum (L. vibrissa, whisker, hair). Modified bryozoan operculum with a seta used to sweep
Veliger larva (Deriv. unknown). Molluscan larva in which the foot and shell make their
Velum (L. curtain, veil). Marginal flap or shelf attached to subumbrella at margin of bell of
Vitillarium (L. vitellus, yolk of egg +arium, place or thing connected with). A structure in the
flatworm ovary which produces yolk eggs.
Zoea (G. zoe, life). The second stage of crustacean larvae.
Zooecium (G. zoe, life +L. ium, nature of). The external covering of bryozoans.
Zoochlorellae (G. zoe., life +chloro, green). Photosynthetic cells which live commensally with
cnidarians and ctenophores.
Zooid (G. zoon, animal +id, nature of).
1. Individual organisms which are attached in a chain-like fashion to form a colony.
2. An individual bryozoan.
Zooflagellates (G. zoon., animal +flagellum, whip). Protozoans which have one or more
flagellae and are without chloroplasts.
Zooxanthellae (G. zoon, animals + xanthos, yellow).
1. Symbiotic dinoflagellates
2. Foreign animals living symbiotically with marine animals.
Zygote (G. zygon, yoke, pair). A cell created by union of two gametes; a diploid form of a
Zygosis (G. zygon, yoke, pair). The process of the union of two zygotes.