Gastropods, Bivalves & Cephalopods Phylum: Mollusca Gastropods, Bivalves & Cephalopods

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.

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)

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

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

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.

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.

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.