Phylum: Mollusca Gastropods, Bivalves & Cephalopods

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

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

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

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

Response/Movement/Reproduction Response- Clams- simple nervous system/eyespot Response- Clams- simple nervous system/eyespot Octopi – brains, complex behavior. Octopi and squid can open jars for reward or to avoid punishment 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. 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. 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. 1. Gastropods – shell-less or single shelled mollusks that move by using a muscular foot. Ex. Sea hares – can squirt ink at predators 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. 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. 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. 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.

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. 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. 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.” They have a pen for a “backbone.”