A Sea Slug or nudibranch is a member of what is now a taxonomic clade, and what was previously a suborder, of soft-bodied, marine gastropod mollusks which shed their shell after their larval stage. They are noted for their often extraordinary colors and striking forms. The clade Nudibranchia is the largest clade within the heterobranchs, with more than 3,000 described species.
The word “nudibranch” comes from the Latin nudus, naked, and the Greek brankhia, gills.
Nudibranchs are often casually called “sea slug”, but many sea slugs belong to several taxonomic groups which are not related to nudibranchs. A number of these other sea slugs (such as the colorful Aglajidae) are often confused with nudibranchs.