A barnacle is a type of arthropod constituting the subclass cirripedia in the subphylum crustacea, and is hence related to crabs and lobsters. barnacles are exclusively marine, and tend to live in shallow and tidal waters, typically in erosive settings. they are sessile (nonmobile) and most are suspension feeders, but those in infraclass rhizocephala are highly specialized parasites on crustaceans. they have four nektonic (active swimming) larval stages. around 1,000 barnacle species are currently known. the name cirripedia is latin, meaning "curl-footed". the study of barnacles is called cirripedology.

Source: Wikipedia