A major phylum of the animal kingdom comprising an extreme diversity of external body forms (oysters, clams, chitons, snails, slugs, squid, and octopuses among others), all based on a remarkably uniform basic plan of structure and function. The phylum name is derived from mollis, meaning soft, referring to the soft body within a hard calcareous shell, which is usually diagnostic. Soft-bodied mollusks make extensive use of ciliary and mucous mechanisms in feeding, locomotion, and reproduction. Most molluscan species are readily recognizable as such.