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.

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

Reproduction Separate sexes External fertilization Young are part of plankton community

Tridacna Clam