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.
Rhizocephala are derived barnacles that parasitise mostly decapod crustaceans, but can also infest Peracarida, mantis shrimps and thoracican barnacles, and are found from the deep ocean to freshwater. Together with their sister groups Thoracica and Acrothoracica, they make up the subclass Cirripedia. Their body plan is uniquely reduced in an extreme adaptation to their parasitic lifestyle, and makes their relationship to other barnacles unrecognisable in the adult form. The name Rhizocephala derives from the Ancient Greek roots ῥίζα and κεφαλή, describing the adult female, which mostly consists of a network of thread-like extensions penetrating the body of the host.
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 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.
Acorn barnacle and acorn shell are vernacular names for certain types of stalkless barnacles, generally excluding Pedunculata. As adults they are typically cone-shaped, symmetrical, and attached to rocks or other fixed objects in the ocean. Members of the barnacle order Balanomorpha are often called acorn barnacles.
Androdioecy is a reproductive system characterized by the coexistence of males and hermaphrodites. Androdioecy is rare in comparison to the other major reproductive systems: dioecy, gynodioecy and hermaphroditism. In animals, androdioecy has been considered a stepping stone in the transition from dioecy to hermaphroditism, and vice versa.
Whale barnacles are species of acorn barnacle that belong to the family Coronulidae. They typically attach to baleen whales, and sometimes settle on toothed whales. The whale barnacles diverged from the turtle barnacles about three million years ago.
Chthamalus is a genus of barnacles that is found along almost all non-boreal coasts of the northern hemisphere, as well as many regions in the southern hemisphere. These small barnacles have been studied in part because of the taxonomic confusion over a group of species that, by and large, are morphologically and ecologically quite similar. In recent years, molecular techniques have identified a number of cryptic species that have been subsequently confirmed by taxonomists using morphological measurements. Most recently the genus has been shown to be paraphyletic, with the genus Microeuraphia nested within Chthamalus.
Dosima fascicularis, the buoy barnacle, is "the most specialised pleustonic goose barnacle" species. It hangs downwards from the water surface, held up by a float of its own construction, and is carried along by ocean currents.
Calanticidae is a family of barnacles in the order Pedunculata, containing the following genera:
Chelonibiidae is a family of turtle barnacles in the order Balanomorpha. There are at least three genera and about eight described species in Chelonibiidae.
Dipterosaccus is a genus of barnacle.
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.
Pseudoctomeris sulcatus is a species of barnacle, the only member of the genus Pseudoctomeris. It has an eight-plated shell wall with the rostrum partially fused with adjacent rostrolatera. The suture lines are visible only from the inside, thus in exterior view, the shell appears to have six wall plates. The basis is calcareous. Opercular plates are higher than wide, and not deeply articulated. These features and others show strong relationship to family Pachylasmatidae, and taxonomic revision of Pachylasmatidae has resulted in the transfer of Pseudoctomeris from Chthamalidae to Pachylasmatidae.
Chamaesipho is a genus of four-plated notochthamaline barnacles in the Pacific Ocean limited to Australian/New Zealand temperate waters. They are intertidal in preference, and tend to form crowded columnar colonies. They can be identified in the field by having a four-plated wall, an unfused rostrum, and narrow opercular plates. Elminius, which also inhabits the same area, has four plates in its shell wall. However, in Elminius, the rostrum and rostrolatera are fused completely, and the compound rostrum receives the alae of the adjacent carinolaterals. In Chamaesipho, the unfused rostrum bears alae, and closely resembles the carina in appearance.
Concavus is a genus of barnacles.
Platylepas hexastylos is a species of barnacle in the family Platylepadidae. It is native to the Indo-Pacific Ocean where it lives as a symbiont of such large marine creatures as the dugong, the green sea turtle, the olive ridley sea turtle, or the loggerhead sea turtle.
Chelonibia testudinaria is a species of barnacle in the family Chelonibiidae. It is native to the Atlantic Ocean, Mediterranean Sea and Gulf of Mexico where it lives as a symbiont on sea turtles, being particularly abundant on the loggerhead sea turtle.
Conchoderma virgatum is a species of goose barnacle in the family Lepadidae. It is a pelagic species found in open water in most of the world's oceans attached to drifting objects or marine organisms.
