A 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.
All known nudibranchs are carnivorous. Some feed on sponges, others on hydroids,(e.g. Cuthona) others on bryozoans (phanerobranchs such as Tambja, Limacia, Plocamopherus and Triopha), and some eat other sea slugs or their eggs (e.g. Favorinus) or, on some occasions, are cannibals and prey on mem
bers of their own species. Other groups feed on tunicates (e.g. Tambja, Nembrotha, Polycera, Thecacera), other nudibranchs (Roboastra, which are descended from tunicate-feeding species),[11] barnacles (e.g. Onchidoris), and anemones (e.g. the Aeolidiidae and other Cladobranchia).
The surface dwelling nudibranch, Glaucus atlanticus is a specialist predator of siphonophores, such as the Portuguese Man O' War. This predatory mollusk sucks air into its stomach to keep it afloat and using its muscular foot it clings to the surface film. If it finds a small victim Glaucus simply envelops it with its capacious mouth, but if the prey is a larger siphonophore the mollusk nibbles off its fishing tentacles, the ones carrying the most potent nematocysts. Like some others of its kind Glaucus does not digest the nematocysts; instead, it uses them to defend itself by passing them from its gut to the surface of its skin.
