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					                              INVERTEBRATE EVOLUTION
                                    CHAPTER 29

 I. Molecular paleontology – the study of how different body plans evolved ---
comparing DNA among living invertebrates to help determine which phyla are most
closely related.

II. This shows the evolution of vertebrates:

The Geological Timetable:
                                               AGE (millions
      ERA:         PERIOD:        EPOCH:         of years               EVENTS:
                               Recent              0.01        Historic time
                               Pleistocene          2.5        Ice ages; humans appear
                                                               Ape-like ancestors of
                               Pliocene             7
                                                               modern humans
                               Miocene              25
  CENOZOIC        Tertiary                                     Origins of most modern
                               Oligocene            38
                               Eocene               54
                               Paleocene            65
                                                               Flowering plants appear;
                               Cretaceous          135
                                                               dinosaurs extinct
                                                               Conifers, mammals & birds
                               Jurassic            190
                                                               appear; dinosaurs dominant
                                                               Mammal-like reptiles
                               Triassic            235
  MESOZOIC                                                     appear
                                                               Origin of most modern
                               Permian             280
                                                               orders of insects
                                                               Origin of reptiles;
                               Carboniferous       345         amphibians & bony fishes
                                                               dominant; first seed plants
                               Devonian            395         First land plants
                               Silurian            450
                               Ordovician          500         First vertebrates
                               Cambrian            570         Origin of most invertebrates
                                                               Approximate age of the
PRECAMBRIAN                                        4600
                                 III. INVERTEBRATES

The first eon of Earth’s history, from the first coalescence of the planet, about 4500 Mya, to
about 542 Mya, is referred to as the Precambrian. From this hint, one might well suppose
that the Cambrian comes next -- which it does, in a way. Actually, this is the biggest break
point in all of geology. It marks the beginning of the Phanerozoic Eon, the Paleozoic Era,
the Cambrian Period, the Terreneuvian Epoch, and the Fortunian Age (the first age of the
Cambrian). The Cambrian Period was named in 1835 by the geologist Adam Sedgwick,
after the region of Cambria in North Wales, where rocks of this age were first found. The
name "Cambria" is a version of Cumbria, a latinisation the Welsh Cymry (= countryman,
compatriot against the invading Anglo-Saxons).

Long before it was a formal stratigraphic unit, the Cambrian was a concept about Earth
history. It was understood to be the earliest period in which one could find the fossils of
multi-celled animals (Metazoa). Since then, metazoans and their fossilized traces have been
found well before 550 Mya. In particular, Ediacarans, a group of very strange and poorly
understood creatures -- but obviously metazoans -- have been found in many parts of the
world with ages pushing the 600 Mya mark.

Consequently, paleontologists now view the Cambrian as the period when the Bilateria first
appeared and, almost at the same time, the first metazoans with shells. The Bilateria include
all living metazoans except jellyfish, corals, and sponges. Bilaterians have a head at one end
of an elongate body which is bilaterally symmetrical (hence the name). Their embryos all
develop a separate layer of embryonic cells, called mesoderm, between the gut or coelom
and the outer wall of the animal. If this whole description suggests a worm, you’ve got the
right idea. A flatworm is the most basal living form of bilaterian.

Unlike many other, somewhat arbitrary, geological markers, the base of the
Cambrian Period is defined with reference to the underlying paleontological
concept. Small worms rarely leave body fossils, but their burrows are frequently
preserved. The burrows of bilaterian worms are fairly distinctive. Trace fossils are
often given names as if they were organisms, and the earliest well-known bilaterian
trace fossil is a type of fossilized burrow referred to as Treptichnus pedum. The base
of the Cambrian is currently defined as the first occurrence of T. pedum at Fortune
Head, near the town of Fortune, on the north coast of western Newfoundland,

 IV>      Invertebrates
   (a)       Most animal phyla are invertebrates (in fact, all but one animal phylum contain
             nothing but invertebrates)
   (b)       Extant animals are grouped into approximately 35 phyla
   (c)       In this survey of the invertebrates we will consider only 10 of these
   Porifera       Cnidaria



  Nematoda        Mollusca
                  Annelida                                   Arthropoda

               Echinodermata                                  Chordata

V. Body Plans or Body Symmetry ---- to see a picture of the animal, click on the link

 1. No symmetry –
        a. Sponge with belongs to the animal kingdom and the phylum Porifera----this
            phylum contains all invertebrates with pore like bodies.
 2. Radial Symmetry – body parts extend from the center of the body
        a. Portuguese Man Of War---this invertebrate belongs to the animal kingdom and
            the phylum Cnidarian----this phylum contains all invertebrates with stinging
            cells in the tentacles
                       Define the following:
                               1. Nematocyst
                               2. Trichocyst
                               3. Hydra
        b. Starfish---this invertebrate belongs to the animal kingdom and the phylum
            Echninodermata----this phylum contains all invertebrates with a spiny type skin
                        Define the following
                                1. Tube feet
                                2. Regeneration
                                3. Radial canal
                                4. Ampullae
 3. Bilateral Symmetry – this basically means that the animal has a mirror image of the left
    and right sides.
 EXAMPLES – click on link
           a. Tapeworms – this invertebrate belongs to the animal kingdom and the phylym
                           Define the following
                                  1. Scolex
                                  2. Hermaphrodite
                                  3. Proglottids
           b. Hook Worm – this invertebrate belongs to the animal kingdom and the phylum
               Nematoda – which means round with NO segments---smooth
           c. Earthworm – this invertebrate belongs to the animal kingdom and the phylum
               Annelida --- which means segmented body
                            Define the following
                                  1. Crop
                                  2. Gizzard
                                  3. Closed Circulatory System
           d. Clam – this invertebrate belongs to the animal kingdom and the phylum
               Molluska---has one or more shells (THIS IS A POWER POINT)
                     Define the following terms:
                              1. Mantle
                              2. Bivalve
                              3. Open Circulatory System
          e. Black Widow Spider – this invertebrate belongs to the animal kingdom and the
phylum Arthropoda…this phylum contains all insects, spiders; it means to have a segmented
                     Define the following
                                 1. Difference between an insect and a spider
                                 2. Cephalothorax
                                 3. Book Lungs
                                 4. Spinnerets
VI. Body Cavities – COELOM

(Mammals the body cavity is called a Coelom and it is the area that contains all heart and
lungs as well as the gut which is a cavity in its own rite. The words used to define different
body cavities relate to how the cavity comes into being during the development of the
embryo as well as to its final observable structure.)

The key words that you need to understand before learning body cavities are as follows:
   Germ Layers
      These layers are a collection of cells that form when the embryo, itself, is developing.
       Germ layers are more known in vertebrates; however, anything more complex than a
Sponge (Porifera), usually have primary germ layers or primary tissue layers.
       Cnidarians, like the Portuguese Man of War, has 2 primary germ layers; we call the two
layers the ectoderm and the endoderm. (TWO LAYERS are usually in radial symmetrical
        Animals with bilateral symmetry have three primary germ layers:
        The germ layers give rise to all of the animals organs and tissues

VII. EXPLANATION of the types of body cavities found in invertebrates
         Coelomates (also known as eucoelomates--"true coelom") have a fluid filled body cavity
          called a coelom (pronounced /ˈsiːləm/) with a complete lining called peritoneum derived
          from mesoderm (one of the three primary tissue layers). The complete mesoderm lining
          allows organs to be attached to each other so that they can be suspended in a particular
          order while still being able to move freely within the cavity. Most bilateral animals,
          including all the vertebrates, are coelomates.

         Pseudocoelomate animals have a pseudocoel, (literally “false cavity”) which is a fully
          functional body cavity. Tissue derived from mesoderm only partly lines the fluid filled
          body cavity of these animals. Thus, although organs are held in place loosely, they are
          not as well organized as in a coelomate. All Pseudocoelomate are protosomes; however,
          not all protosomes are Pseudocoelomates. An example of a Pseudocoelomate is the
          roundworm. Pseudocoelomate animals are also referred to as Hemocoel and

         Acoelomate animals, like flatworms, have no body cavity at all. Organs have direct
          contact with the epithelium. Semi-solid mesodermal tissues between the gut and body
          wall hold their organs in place.
         Terms needed for the first part of chapter 29

    1.    Cephalization
    2.    protosomes
    3.    coelom
    4.    acoelomate
    5.    pseudocoelom
    6.    dorsal
    7.    ventral
    8.    bilateral symmetry
    9.    radial symmetry
    10.   fossil
    11.   invertebrate
    12.   names of each of the phylums
    13.   germ layers
    14.   Cambrian Era

    VI.       Each type of invertebrate has systems to keep it living

The simplest animals break down food primarily through intracellular digestion, whereas more
complex animals use extracellular digestion.
   Respiratory organs have large surface areas that are in contact with the air or water. In order
for diffusion to occur, these respiratory surfaces must be kept moist.
   Most complex animals move fluid through their bodies using one or more hearts and an open
or closed circulatory system.
   Most animals have an excretory system that rids the body of metabolic wastes and controls the
amount of water in their tissues.
   Invertebrates show three trends in the evolution of the nervous system: centralization,
cephalization, and specialization.
   Invertebrates have one of three main kinds of skeletal systems: hydrostatic skeletons,
exoskeletons, and endoskeletons.
  Most invertebrates reproduce sexually during at least part of their life cycle. Depending on
environmental conditions, however, many invertebrates may also reproduce asexually.

          a. Intracellular digestion – this is when the organism brings in food by way of
              Phagocytosis; it is found in sponges and the cnidarians…jelly fish, Portuguese
              man of War, etc.
 - this link will show you
          b. Extra cellular digestion – this is when the organism secretes enzymes through a
              membrane to digest the food it took in. These small particles that have been
              broken down are small enough now to be phagocyzed. The resulting product is
              transported throughout the organism by blood or body fluid.
          c. Simplest animals tend to use intracellular digestion. More complex animals tend
              to use extra cellular digestion, in which food is broken down in a digestive
          d. Simplest digestive systems have just one opening through which food is taken in
              and wastes are expelled. More complex digestive systems have two openings -- a
              mouth and an anus.


            a. Aquatic invertebrates – the oxygen in the water, that the invertebrate lives, has
               Oxygen in it. This Oxygen diffuses into the body; carbon dioxide, a waste
               product formed in the invertebrates body, diffuses out.
            b. Terrestrial invertebrates---these invertebrates bring Oxygen in through
               specialized openings OR their skin is moist.
            c. Respiratory systems require a thin moist membrane and a large surface area for
               effective gas exchange

            a. Open circulatory system----this type of invertebrate has no arteries and veins; the
               blood is colorless…has no hemoglobin
            b. Closed Circulatory system – the fluid/blood stays within arteries and veins; blood
               is red because it has the red pigment hemoglobin in it.

    IX.     RESPONSE – stimulus leads to a response (irritability)
            a.      Three trends in the evolution of the nervous system are centralization,
               Cephalization, and specialization
            b. Specialization ---some animals like the Cnidarians (Jelly Fish, Portuguese Man
               of War, have a nerve net as its nervous system---it is a loosely organized system
               of nerves with NO central control. Impulses are conducted in both directions
               causing the movement of the invertebrate.
            c. Cephalization---this is an evolutionary trend; it shows that the nervous tissue
               becomes more concentrated toward one end of an organism; this leads to sensory
               organs. This occurs with bilateral symmetrical invertebrates
                                     Nervous System
                             Although the ameba is a single-celled
                             animal, it does appear to be sensitive to
 Ameba/Paramecium            the environment. This tiny animal moves
                             away from light, but it has no
                             photodetectors or eyes. The paramecium,
                             another single-celled animal, also has no
                             specialized sensory structures. However,
                             it avoids cold, heat and chemicals by
                             backing up and moving away.

                             Euglena have an eyespot that acts as a
                             shield for a light sensitive receptor. This
  Euglena (flagellate)       small animal can detect the strength and
                             direction of light. It prefers a location
                             with moderate light and moves away
                             from darkness and bright light. Euglena
                             probably use this receptor to keep
                             themselves in light which they use for
                             photosynthesis. Euglena use
                             photosynthesis for energy although they
Image courtesy of Biodidac   can eat solid food (like animals) if they
                             are kept in the darkness.


                             Sponges are the only multicellular
                             animals without a nervous system. They
                             do not have any nerve cells or sensory
                             cells. However, touch or pressure to the
                             outside of a sponge will cause a local
                             contraction of its body.

Image courtesy of Biodidac

                             The hydra has a nervous system
                             characterized by a nerve net. A nerve net
         Hydra               is a collection of separate, but
                             "connected" neurons. Neurons are
                             connected by synapse. Communication
            between neurons can be in both directions
            at the synapse within a nerve net. The
            nerve net is concentrated around the
            mouth. Unlike higher animals, the hydra
            does not have any grouping of nerve cell
            bodies. In other words, there are no

              The hydra does have specialized
              cells for touch and chemical

            Like the hydra, the jellyfish has a nervous
            system characterized by a series of
            interconnected nerve cells (a nerve net).
            The nerve net conducts impulses around
            the entire body of the jellyfish. The
            strength of a behavioral response is
            proportional to the stimulus strength. In
            other words, the stronger the stimulus, the
            larger the response.

              Some jellyfish (for example,
              Aurelia) have specialized structures
Jellyfish     called "rhopalia". These rhopalia
              have receptors for:

                  light (called ocelli)
                  balance (called statocysts)
                  chemical detection (olfaction),
                  touch (called sensory lappets)

                                                    is a
            st. When the animal moves and body is
            tilted, the statocyst makes contact with
            the cilium. When the cilium bends, it
            causes action potentials to fire in a nerve.
            This provides information to move


                       Like the jellyfish and hydra, the anemone
                       has a nerve net.

                       The nervous system of the flatworm has
                       an organization different from the
                       invertebrates describe above. It does have
Flatworms (Planaria)   a nerve net, but these are connected by
                       long nerve cords. These cords are
                       connected to cerebral ganglia located in
                       the head region. The central nervous
                       system has been described as "ladder-
                       like" because of the nerves connecting the
                       nerve cords.

                         Flatworms have "auricles" that
                         project from the side of the head.
                         These auricles contain
                         chemoreceptors that are used to find
                         food. Flatworms also have eyespots
                         called "ocelli". The ocelli are
                         sensitive to light and are connected
                         to the cerebral ganglia. Generally,
                         the flatworm avoids light.

                       The nervous system of the earthworm is
    Earthworm          "segmented" just like the rest of the body.
                       The "brain" is located above the pharynx
                       and is connected to the first ventral
                       ganglion. The brain is important for
                       movement: if the brain of the earthworm
                       is removed, the earthworm will move
                       continuously. If the first ventral ganglion
                       is removed, the earthworm will stop
                       eating and will not dig. Each segmented
                       ganglion gets sensory information from
                              only a local region of its body and
                              controls muscles only in this local region.

                                Earthworms have touch, light,
                                vibration and chemical receptors all
                                along the entire body surface.

                              The nervous system of the starfish is very
                              simple...there is no brain and there are not
                              even any ganglia to coordinate
        Sea Star              movement. The nervous system is
      ("Starfish")            characterized by a nerve ring that
                              surrounds the mouth. A radial nerve
                              branches off of the nerve ring and extends
                              to each arm. The picture on the left shows
                              one of 3 nerve nets that extend
                              throughout the body.

                                Starfish have an interesting way of
                                detecting light. They have
                                "eyespots" at the tip of each arm.
                                The eyespot contains light sensitive
                                pigments that allow the starfish to
                                detect shadows and changes in the
                                brightness of light.

          Snails              The nervous system is characterized by 6
                              ganglia. Some snails have chemosensors
                              called "osphradia" in the mantle cavity.
                              These osphradia are used to detect
                              chemicals in the air or water.

                              The aplysia has several ganglia that are
       (Sea Hare)             connected by long nerves. The cell bodies
                              of some neurons are very large (1 mm in
                              diameter). Neuroscientists like these cells
                              because they are easy to: 1) see 2) record
                              action potentials 3) inject chemicals.
Image courtesy of BrainSurf

                              The nervous system is comprised of 3
                              pairs of ganglia (cerebral, visceral and
    (clams, scallops)         pedal) each associated with the
                         esophagus, muscles close to the shell, and


                         The crab has a condensed central nervous
                         system consisting of several ganglia.

                         The lobster has a brain connected to a
                         first ventral ganglion. This ganglion is
                         located under its stomach. A double nerve
                         cord extends from the first ventral
                         ganglion to a series of paired segmental
                         ganglia running through the entire body
                         on the ventral side of the animal.

                         The grasshopper has a brain located
                         between its eyes, just above the
                         esophagus. The brain is connected to the
                         1st ventral ganglion by a pair of ventral
                         nerves that surround the gut. The
                         grasshopper can do many things, like
                         walking and jumping, WITHOUT its
(such as grasshoppers)   brain. The brain is used to relay sensory
                         information to other parts of the body and
                         to help with movement. The first ventral
                         ganglion is used primarily to control
                         movement of the mouth. The segmental
                         ganglia throughout the length of the
          grasshopper are connected to the first
          ventral ganglion by a double nerve cord
          and serve to coordinate local activities.

            Insects have a compound eye
            containing many different units
            called "ommatidia". Each ommatidia
            is like an individual lens that
            samples a small part of the visual
            field. There can be thousands of
            ommatidia in a single insect eye.
            Science fiction/horror/monster
            movies that show an insect that sees
            thousands of identical images of the
            ENTIRE visual field are WRONG --
            an insect sees only ONE picture at a
            time because each ommatidia sees
            only a small part of the entire field.
            Some insects are sensitive to
            ultraviolet light and others can detect
            infrared wavelengths of light.

          The octopus has the most complicated
          brain of all the invertebrates. The octopus
          brain is estimated to have 300,000,000
          neurons. These neurons are arranged in
          lobes and tracts that are more specialized
          than simple ganglia. An octopus has a
          "good" memory and can also learn.

Octopus     The eye of the octopus is very
            similar to that of vertebrates in that it
            has a cornea, lens, iris and retina. It
            can also focus and form images.
            However, the octopus eye is
            different from that of vertebrates in
            that it focuses light by moving the
            lens closer and further away from
            the retina. The vertebrate eye
            focuses by changing the shape of the
            lens. Octopi can perceive shape,
            color intensity and texture. Another
            difference is that the eye of the
            octopus has NO blind spot because
            the nerve cells leave from the
                                                      outside of the eyeball. The octopus
                                                      also has a statocyst located next to
                                                      the brain. The statocyst is used to
                                                      detect changes in gravity and
                                                      respond to acceleration.

Excretory systems regulate the amount of water in the body and dispose of nitrogenous
   A.      Protozoan and sponges- lack complex excretory organ
            1. Contractile vacuoles excrete water and solutes
            2. Depends on ambient osmotic conditions- contracts more frequently and expels
            more water in fresh H2O

      B.     Flatworms- branched longitudinal tubules in a hollow bulb
               Cilia inside bulb create currents within cell (flame cells)- fluid and waste carried
                out through excretory pores.

      C.     Mollusks- have protonephridia or metanephridia-
             1. Freshwater animals- nephridia produce a copious hypo osmotic urine- excrete
               water, conserve ions
               2. In marine animals- urine- iso-osmotic with body fluid, vol. low to conserve

      D.   Crustaceans- rely primarily on antennal and maxillary glands for solute excretion.
              Urine is formed by filtration at the terminal coelom-sac, which has an arterial;
      blood supply.

      E. Earthworms- closed circulatory system- excretion is carried out by nephridia.
            1. Body fluid enter nephridium through the membrane of the bulb-like
                nephrostome, which is ciliated opening into the nephridium
            2. The nephridium gives rise to a coiled tubule, which is closely associated with
            blood capillaries,
            3. This allows reabsorption of material; the nephridium terminates in a large
            bladder that opens to the outside by nephridiopore

      F. Insects- excretory structure- Malpighian tubules forms urine by active K+ secretion
                  into the tubules, water and solutes follow passively.
             1. Tubules are out pocketing of the gut at the junction of the midgut and
               the hindgut.
             2. These sacs are washed by the blood, fluids and salts are reabsorbed.
             3. The urine formed moves into the hindgut and out of body through
                the rectum.
             4 Both feces and urine exit through the anus where water is reabsorbed

           a. Asexual reproduction makes it possible for one individual to rapidly produce
              many genetically identical offspring. Sexual reproduction creates new
              combinations of genes.
       b. Fertilization may be internal or external.
       a. Hydrostatic Skeleton --- is a structure found in many cold-blooded
          organisms and soft-bodied animals consisting of a fluid-filled cavity, the
          coelom, surrounded by muscles. The pressure of the fluid and action of the
          surrounding muscles are used to change an organism's shape and produce
          movement, such as burrowing or swimming. Hydrostatic skeletons have a
          role in the locomotion of echinoderms (starfish, sea urchins), coelenterates
          (jellyfish), annelids (earthworms), nematodes, and other invertebrates.
       b. Sea anemones and earthworms do not have a single bone in their bodies.
          Instead, they are supported by pressure from a liquid which consists
          mainly of water in their cells and in spaces between their body. The
          hydrostatic skeleton allows the earthworm to burrow through the earth.
          They have some similarities to muscular hydrostats.
       c.   Exoskeleton ---- an outer covering is found over the outside of the invertebrate.
            An exoskeleton is a type of skeleton that is an external anatomical feature
            that supports and protects an animal's body, in contrast to the internal
            endoskeleton of, for example, a human. Whilst many, many other
            invertebrate animals (such as shelled mollusks) have exoskeletons in the
            sense of external hard parts, the character is most associated with the
            arthropods (i.e. insects, spiders, myriapods and crustaceans). Exoskeletons
            contain rigid and resistant components that fulfill a set of functional roles
            including protection, excretion, sensing, support, feeding and (for
            terrestrial organisms) acting as a barrier against desiccation. Exoskeletons
            first appeared in the fossil record about 550 million years ago, and their
            evolution has been seen as a critical driving role in the Cambrian
            explosion of animals that took place subsequent to this time.
       d. Endoskeleton – a skeletal structure within a body; common to invertebrates

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