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|Noun||1.||Nudibranchia - comprising numerous marine gastropod mollusks lacking a shell in the adult state and usually having a body like a slug|
animal order - the order of animals
Opisthobranchia, subclass Opisthobranchia - gastropods having the gills when present posterior to the heart and having no operculum: includes sea slugs; sea butterflies; sea hares
nudibranch, sea slug - any of various marine gastropods of the suborder Nudibranchia having a shell-less and often beautifully colored body