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Mollusks - BiologyJunction



      The mollusks are members of the large and diverse phylum
Mollusca, which includes a variety of familiar animals well-known for
their decorative shells or as seafood. These range from tiny snails,
clams, and abalone to larger organisms such as squid, cuttlefish,
chambered nautilus, and the octopus (the most intelligent mollusk).
The vast majority of mollusks live in marine environments, mainly on
the coastal plains. However, two groups, the bivalves and the
gastropods, also contain freshwater species, and only the gastropods
have representatives that live on land (snails and slugs).


      Chitons are mollusks that along ocean coastlines in most of the
world, but some species have been found in deep water. They creep
along slowly on their muscular feet and cling to rocks. Chitons have
shells made up of overlapping plates. The shell is divided into eight
plates embedded in the tough muscular girdle that surrounds the
chiton's body. Label and color the girdle tan and the plates dark
green. This arrangement allows chitons to roll into a protective ball
when dislodged and to cling tightly to even irregular surfaces.

Chambered Nautilus

The Chambered Nautilus is the best known species of nautilus. The
spiral shaped shell, when cut away, reveals a lining of shiny mother-
of-pearl. The nautilus has primitive eyes compared to other
cephalopods, mostly due to the fact that they have no lens. It has
about 90 tentacles and NO suckers which is also different from other
cephalopods. This nocturnal animal has a pair of rhinophores, which
detect chemicals and uses smell to find its food. Color the shell
sections of the nautilus tan and brown.

             Chiton                    Chambered Nautilus

                          Cephalopod Mollusk

      The word octopus means "eight feet." Octopi (plural form) are
solitary animals with arms or tentacles that have suckers. They live
on the ocean floor. There are over 100 different species of octopus.
The Giant Octopus is the biggest octopus. This huge mollusk is up to
23 ft (7 m) from arm tip to arm tip, weighing up to 400 pounds (182
kg). The smallest is the Californian octopus, which is only 3/8 inch (1
cm) long.
An octopus has a soft body (visceral mass) and eight arms. The soft
body is covered by a protective layer called the mantle. Label and
color the head and mantle dark blue. Each arm has two rows of suction
cups. If it loses an arm, it will eventually regrow (regenerate) another
arm. Label and color the arms gray and the suckers pink. It has blue
blood. An octopus has an eye on each side of its head and has very
good eyesight. Label and color the eye yellow. An octopus cannot
hear. Octopi eat small crabs and scallops, plus some snails, fish,
turtles, crustaceans (like shrimp), and other octopi. They catch prey
with their arms; kill it by biting it with their tough beak, paralyzing

the prey with a nerve poison, and softening the flesh. Color and label
the beak red. They then suck out the flesh. Octopi hunt mostly at
night. Only the Australian Blue-ringed octopus has a poison strong
enough to kill a person. Octopi live in dens, spaces under rocks,
crevices on the sea floor, or holes they dig under large rocks. Octopi
pile rocks to block the front of their den. The den protects them from
predators (like moray eels) and provides a place to lay eggs and care
for them (a mother octopus doesn't eat during the entire 1 to 2
months she is caring for her eggs). In order to escape predators, an
octopus can squirt black ink into the water, allowing the octopus to
escape. Another defense that octopi have is changing their skin color
to blend into the background, camouflaging them. The octopus swims
by spewing water from its body through a siphon, a type of jet

Read the definitions and the color and label the squid diagram below:
Arms - eight short limbs, each of Feeding tentacles - the two, long
which has two rows of suction cups tentacles are used for obtaining
on the lower side; the arms hold    prey; they have toothed suckers
the food while the squid bites it   only near the tip
into swallowable pieces
Beak and mouth - the parrot-like Head - the small part of the body
beak on the mouth is used for       between the mantle and the arms;
biting food into small pieces. The the head contains the eyes, the
beak and mouth are surrounded by brain, and the muscular buccal
the bases of the arms and           mass, which crushes the food
Clubs - the ends of the tentacles, Mantle - the large part of the
which have toothed suckers          squid in front of the head; inside
                                    the mantle are the stomach, gills,
                                    ink sac, pen, reproductive organs,
                                    and many digestive organs
Eye - an organ used to see; squids Siphon - a tube-like organ on the
have two, very large eyes; they are lower side of the head; it expels
large in proportion to the size of  water forcefully, enabling the
the body                            squid to propel itself through the
Fins - two flaps on the mantle that
are used to stabilize the squid
during swimming

                          Gastropod Mollusk
Read the definitions and the color and label the land snail diagram
eyespots - located at the tips mouth - on the underside of the head -
of the long tentacles on land it contains the radula, a file-like tongue
snails (red)                   that breaks down the snail's food

foot - the soft, muscular part respiratory pore - a small hole in the
of the snail that allows the   side of the body, used for breathing
snail to move (tan)            (green)

shell - the hard, spiral,          tentacles - two long and two short
protective covering of the         sensory tentacles on the upper surface
snail (brown)                      of the snail's head (Purple)

head - the front part of the
snail, containing the tentacles,
eyes, and mouth (gray)

                             Bivalve Mollusk
      Clams are animals that burrow under the sea floor. They are
bivalves, mollusks that have two shells that protect a soft body. The
oldest and highest part of the clam shell is called the umbo. Label the
shell and the umbo. The clam's shell is laid down in rings. The rings
close to the furthest from the umbo are the newest. Label and color
the rings red-brown. The biggest clam is the Giant Clam is up to 4.8
feet (1.5 m) long and weighs up to 550 pounds (250 kg). Most clams are
only a few inches long. Clams come in many colors, including shades of
brown, red-brown, yellow, cream, etc. The two shells are attached by a
muscular hinge and open and close with the help of an adductor muscle.
Label and color the muscular hinge orange. When a clam is
threatened, most clams will pull their soft body into the shells and
close the shells tightly for protection. The foot is used to burrow into
the sand. The foot can be extended outside the shells or valves.
Color and label the foot light blue. Clams use their tube-like siphon to
draw in water, from which they extract oxygen and filter plankton
(tiny plants that they eat.) Clams have both an incurrent and
excurrent siphon for water to enter and leave. Label and color the
siphons pink. The neck and soft body are at the base of the siphons.
Label the neck and soft body.

1. Define visceral mass and tell what protects it.

2. Name mollusks with a shell.

3. Name mollusks without a shell.

4. The foot of cephalopods is modified into ________________.

5. How do aquatic mollusks breathe?

6. Gastropods undergo torsion as they develop. Use your textbook to
help explain the process.

7. What opens and closes bivalve shells?

8. How do bivalves feed?

9. Give 2 defense mechanisms used by octopi.

10. How do squid and octopus move quickly away from predators?

11. What is the most intelligent mollusk?

12. Do mollusks go through larval stages? Explain your answer.

13. What type of circulatory system is found in most mollusks?
14. Explain the circulatory system of cephalopods.


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