Phylum Mollusca

Phylum Mollusca Soft bodied Bilateral symmetry Head, foot, and coiled visceral mass Most have external or internal shell Brain Coelom: fluid filled cavity Over 100,000 species

Class Bivalvia (Bivalves) Two shells hinged together by adductor muscles Prey to sea stars, predatory snails and humans

Shell Lines on shells represent age (like tree rings) Made of calcium carbonate Produced by mantle-thin membrane inside shell Mantle also makes pearls by reacting to a grain of sand.

Siphon Tube Protrudes through gap btwn the clam’s shell Used for breathing and feeding Two openings Incurrent siphon allows water containing food and O2 in Excurrent siphon allows water containing wastes and CO2 out

Respiration Gills- membranes that take in O2 and give off CO2 Microscopic cilia beat to create a current on gills.

Feeding and Digestion Filter feeding: currents of water that contain plankton and organic debris pass into the clam through it’s incurrent siphon, propelled by the ciliary action of gill surfaces. Cilia move the food into the clam’s mouth and into a one-way digestive tract.

Circulation Open circulatory system: nutrients and O2 transported by a colorless blood.

Reproduction Separate sexes External fertilization Young are part of plankton community

Movement Mussels: live in turbulent intertidal zone w/ constant wave action. Attach with fibrous protein secreted by foot Oysters: bottom shell secretes a cement like substance Use muscular foot to dig in sand Contract and relax adductor muscles Scallops

Tridacna Clam

Class Gastropoda Snails, sea slugs (nudibranchs), limpets, abalone Gastropoda: one shell “univalve” Shells are made of calcium carbonate and may have an operculum: covering of the shell opening that closes like a trap door over its foot.

Respiration Gills take up oxygen from the water through the siphon tube. Absorbs O2 and releases CO2.

Feeding Styles Snails use a radula (ribbon like toothed structure)to feed. Herbivores- (ex. Periwinkle) graze on algae Scavenger-(mud snail) feed on dead or dying organisms. Use radula to tear and shred the dead matter into small pieces.

Feeding Styles Predator- actively hunt and kill their food. Ex moon snail- feeds on live clams by secreting chemical to soften the shell and then eat the animal inside. Ex. Cone snail-uses toxins from its harpoon-like radula to kill its prey.

Cone Snail

Circulation Open circulatory system w/ a one chambered heart and tiny blood vessels.

Movement Carried out by the nervous and muscular system working together. Signals sent from brain to motor nerves.

Reproduction Many different methods Some have separate sexes; some are hermaphrodites Fertilization is internal; development is external. Many different methods: Welk has egg casings; moon snail has sand collar; mud snail has transparent jelly capsules.

Reproduction Egg casing of welk  Sand collar

Gastropod Diversity Abalone- produces mother of pearl used for jewelry Slipper shell- live in intertidal zone attached to any hard substrate (even horshoe crab); change from male to female and stack themselves up. (Crepidula)

Gastropod Diversity Limpet- intertidal zone of rocky coasts; looks like a flattened cone. (hole on top of shell for wastes to exit)

Gastropod Diversity Nudibranch (sea slug)- lack or have a reduced shell; breathe through skin w/ tufts of gills on their backs; eat hydroids and anemones and use their stinging as part of their defense; very colorful to serve as a warning. Sea hare eat algae and some turn green from all the chlorophyll they consume.

California Sea Hare 75 cm in length= largest gastropod in ocean!!!! Releases a dye when disturbed 

Pteropoda Important zooplankton Affected by rising CO2 in the oceans This shells of calcium carbonate are eaten away by the carbonic acid formed because of too much CO2