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 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.
Thoracica is an infraclass of crustaceans which contains the most familiar species of barnacles found on rocky coasts, such as Semibalanus balanoides and Chthamalus stellatus. They have six well-developed limbs, and may be either stalked or sessile. The carapace is heavily calcified. The group includes free-living and commensal species.
Thecostraca is a class of marine invertebrates containing over 2,200 described species. Many species have planktonic larvae which become sessile or parasitic as adults.
The Balanidae comprise a family of barnacles of the order Balanomorpha. As a result of research published in 2021 by Chan et al., the members of the family Archaeobalanidae were merged with this family.
The Chthamalidae are a family of chthamaloid barnacles, living entirely in intertidal/subtidal habitats, characterized by a primary shell wall of eight, six, or four plates, lacking imbricating plate whorls, and either membraneous or more rarely calcareous basis. They are not found below immediate subtidal habitats, and more likely are found in the highest tier of shallow-water barnacle fauna. They can be found in the most rigorous wave-washed locations, and some species are found in the surf zone above high tide mark, only receiving water from wave action at high tide.
The Balanomorpha are an order of barnacles, containing familiar acorn barnacles of the seashore. The order contains these families:
Elminiidae is a family of symmetrical sessile barnacles in the order Balanomorpha. There are about 5 genera and 12 described species in Elminiidae.
Calanticidae is a family of acorn barnacles in the order Calanticomorpha. There are about 12 genera and more than 60 described species in Calanticidae.
The Chthamaloidea are a subdivision of Balanomorpha proposed by Newman and Ross to include barnacles with shell wall composed of rostrum, carina, and one to three pairs of latera, rarely supplemented with one or more whorls of basal imbricating plates. The rostrolatus enters the sheath, but rarely fuses with the rostrum, as in the three higher superfamilies. Shell plates are simple in construction, solid, and incorporate organic chitin between carbonate layers. Opercular plates are deeply interlocked, and in some genera, may become concrescent with age. Soft part morphology includes concave labrum without notch in the central part. Cirrus III more resembles Cirrus IV than II, or may be intermediate in structure. Caudal appendages present in some species.
The Catophragmidae are a family of barnacles in the superfamily Chthamaloidea with eight shell wall plates, surrounded by several whorls of imbricating plates. The basis is membranous.
The clade Multicrustacea constitutes the largest superclass of crustaceans, containing approximately four-fifths of all described crustacean species, including crabs, lobsters, shrimps, woodlice, prawns, krill, barnacles, crayfish, copepods, amphipods and others. The largest branch of multicrustacea is the class Malacostraca.
Scalpellidae is a family of acorn barnacles in the order Scalpellomorpha. There are about 25 genera and 220 described species in Scalpellidae.
Malacolepadidae is a family of acorn barnacles in the order Scalpellomorpha. There are at least two genera and two described species in Malacolepadidae.
Pachylasmatidae is a family of symmetrical sessile barnacles in the order Balanomorpha. There are about 10 genera and at least 30 described species in Pachylasmatidae.
Lithoglyptida is an order of barnacles in the class Thecostraca. There are 2 families and more than 40 described species in Lithoglyptida.
Iblomorpha is a small order of barnacles in the class Thecostraca. There are only two families and about eight described species in Iblomorpha.
Calanticomorpha is an order of acorn barnacles in the class Thecostraca. There are 3 families and more than 90 described species in Calanticomorpha.
Pollicipedomorpha is an order of pedunculated barnacles in the class Thecostraca. There are 3 families and more than 30 described species in Pollicipedomorpha.
Eochionelasmus is a genus of symmetrical sessile barnacles in the family Chionelasmatidae. There are at least two described species in Eochionelasmus.
