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.”
