1. one of the leading divisions of invertebrated animals; an extensive series of invertebrates whose bodies are soft, without any jointed legs, and commonly covered with a hard shell in one, two, or more pieces, and whose principal parts are neither segmented into a series of longitudinal rings, as in insects, crustaceans, and worms, nor radiately arranged, as in echinoderms; the mollusks, as the univalve or bivalve shell-fish of ordinary language.

1. gastropods; bivalves; cephalopods; chitons