The scientific name of a sea slug is "Nudibranchia". The name "Nudibranchia" is Latin for naked gills. This refers to the animal’s lack of a shell as well as the feather-like gills and horns on its body. These animals are also called gastropod mollusks and pteropods.

There are over 2,000 species of sea slug. In short, sea slug is a common name standing for many types of these animals. They belong to the Gastropoda class, the family of Opistobranches and are in the phylum Mollusca.

More Info: a-z-animals.com