Mollusc shell

Common card · No. 486335

The mollusc (or mollusk) shell is typically a calcareous exoskeleton which encloses, supports and protects the soft parts of an animal in the phylum Mollusca, which includes snails, clams, tusk shells, and several other classes. In this phylum, the shell takes on various forms: in Gastropoda, many species bear the archetypical coiled shell of snails, while Bivalvians typically have two shells known as valves. In various groups, the shell has been reduced, often internalized and encased within the soft tissue, which is seen in slugs, sea slugs, and cephalopods of the subclass Coleoidea. The ancestral mollusc is thought to have had a shell, but this has subsequently been lost or reduced on some families, such as the squid, octopus, and some smaller groups such as the caudofoveata and solenogastres. Today, over 100,000 living species bear a shell; there is some dispute as to whether these shell-bearing molluscs form a monophyletic group (Conchifera) or whether shell-less molluscs are interleaved...

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