In form Mollusca, with singular or plural agreement. Originally: a heterogeneous group of mostly shell-less invertebrates, forming the second order of the class Vermes in Linnaeus's classification (Systema Naturae (ed. 10, 1758) I. vi. ii. 652) and including cephalopods, echinoderms, hydroids, slugs, and annelids. Now, mainly following the classification proposed by Cuvier in 1788–1800: a phylum of invertebrates that live in aquatic or damp habitats and have a soft, unsegmented body and usually an external calcareous shell. Also, with plural agreement (also mollusca): animals of this phylum (collectively or individually).