Phylum Molluska

Characteristics of Mollusks•Aquatic (freshwater, marine) & Terrestrial

•External or internal shell or no shell

•Size: small (i.e. grain of sand) to large (20 meter squid)

•Bilateral Symmetry

Circulatory System of Mollusks•Open in most, blood not confined to

vessels (example: snails, slugs)

•Closed in others, blood is confined to vessels(example: squid, octopi)

Larvae = trochophore•Free swimming

•Young form of animal

•Looks and behavesdifferently fromadult

Body Plan of ALL Mollusks•FOOT - used for movement; contains

mouth

•VISCERAL MASS - internal organs

•SHELL – made of calcium carbonate; not all mollusks have

•MANTLE – a thin membrane that surrounds and secretes the shell

Reproduction – mainly external fertilization

•Most are separate sexes▫Release sperm and eggs into the water

•Some are hermaphrodites▫Some water snails and some oysters

•Land mollusks have internal fertilizations ▫Male has a penis to transfer sperm

Class Bivalvia“Bivalves”

Bivalvia (Clam, oyster, scallop, mussel)•Have 2 VALVES (shells) held together by a

ligament held together

•Shell stays shut by adductor muscles

•They are FILTER FEEDERS▫Food and water enter the incurrent siphon; food

taken in by mouth▫Can accumulate toxins from the surrounding

environment

•GILLS for respiration

Mussels attach to rocks with their BYSSUS THREADS (sessile)

Scallops FLAP their shells to swim

•http://www.youtube.com/watch?v=_2iXHBuSIJY

Clams burrow into sand/mud with their FOOT

•http://www.youtube.com/watch?v=HrBijKf0Ywk