From scallop to sea slug, invertebrates have served as models of human and animal disease.
British Dictionary definitions for sea slug
sea slug
noun
1.
any of various shell-less marine gastropod molluscs, esp those of the order NudibranchiaSee nudibranch
sea slug in Science
sea slug Any of various colorful marine gastropods of the suborder Nudibranchia, lacking a shell and gills but having fringelike projections that serve as respiratory organs. Also called nudibranch.