Invertebrate Phylum

Mollusca

(Mollusks)

Vocabularyvisceral mass = contains internal

organs of digestion, excretion, and reproduction

mantle = thin membrane that surrounds internal organs

VocabularyRadula = tongue-like structure

with teeth used to grate, cut, and scrape

Torsion =visceral mass twists 180* in relation to head

Siphon = fleshy tubes for movement of water in a mollusk

Characteristicstrue coelm

* bilateral symmetry* two body openings

* 3 body parts: head, muscular foot, visceral mass

* most have shell secreted by mantle* gills for gas exchange with water* some have a radula for feeding

Gastropoda: "stomach foot"

* single shell - snails, abalone, conch* no shell - nudibrachs, slugs* move by muscular contractions of

foot* open circulatory system

Bivalvia: shell with "two valves”* clams, oysters, scallops

* strong muscle for pulling shell and burrowing

* no head or radula* filter food from water via gills; cilia

move food to stomach

Cephalopoda: "head-foot”

* octopuses, squid, nautilus* free swimming; predatory; tentacles

with suckers* radula and sharp beak* large brain and advanced nervous

system* closed circulatory system