molluska

1. Phylum:
Mollusca
Gastropods, Bivalves & Cephalopods

2. Mollusks
 Mollusks are soft-
bodied animals that
usually have an internal
or external shell.
 Ex. Clams, squid,
octopi, mussels,
nudibranchs.
 They have a free
swimming larval stage
called a trochophore.

3. Body Plan – 4 parts
 1. foot – used for crawling, burrowing and
tentacles
 2. mantle – thin layer of tissue that covers
organs
 3. shell – made by glands in the mantle that
secrete calcium carbonate
 4. visceral mass – guts. (internal organs)

4. Feeding
 Feeding – radula –
ribbon of teeth
 Others are filter feeders
using an incurrent and
excurrent siphon

5. Respiration and Circulation
 Respiration – gills
 Circulation - Open circulatory system – heart
and open sinuses. Open works for slow moving
creatures
 Closed circulatory system – blood is contained
in veins and arteries. Octopi and squid

6. Response/Movement/Reproduction
 Response- Clams- simple nervous system/eyespot
 Octopi – brains, complex behavior. Octopi and
squid can open jars for reward or to avoid
punishment
 Movement – mucus with the foot/muscle or jet
propulsion for the octopus.
 Reproduction – usually external fertilization in the
water. Some tentacled mollusks do internal
fertilization. Some can be hermaphrodites.

7. 3 main groups of Mollusks
 1. Gastropods – shell-less or
single shelled mollusks that move
by using a muscular foot.
 Ex. Sea hares – can squirt ink
at predators
 Nudibranches – sea slugs,
have chemicals in their bodies that
taste bad. Can recycle
nematocysts from cnidarians they
eat.

8. 3 main groups of Mollusks
 2. Bivalves – two shells held together by two
powerful muscles.
 Ex. Clams, oysters, mussels and scallops.
Scallops can flap their shells to move when
threatened. Filter water over gills use mucus and
cilia on gills to trap food particles.

9. 3 Main Groups of
Mollusks
 3. Cephalopods – “head-footed” . Soft bodied.
The head is attached to a single foot. The foot is
divided into tentacles or arms.
 Example: squid, octopus, nautilus, cuttlefish.
They move by jet propulsion. Many have an ink
sac to distract potential predators.
 They have a pen for a “backbone.”