Definition: 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]
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