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A phylum of the subkingdom Metazoa with soft, unsegmented bodies, consisting of an anterior head, a dorsal visceral mass and a ventral foot. Most forms are enclosed in a protective calcareous shell. Mollusca includes the classes Gastropoda (snails, whelks, slugs), Pelecypoda (oysters, clams, mussels), Cephalopoda (squids, octopuses), Amphineura (chitons), Scaphopoda (tooth shells), and the class of primitive metameric mollusks, Monoplacophora.
[L. mollusca, a nut with a thin shell, fr. mollis, soft]
A phylum of animals that includes the bivalves (mussels, oysters, clams), slugs, and snails. Snails are intermediate hosts for many parasitic flukes. Oysters, clams, and mussels, esp. if inadequately cooked, may transmit the hepatitis A virus or bacterial pathogens.