''Anelasma'' is a

monotypic genus In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispec ...

goose barnacle Goose barnacles, also called stalked barnacles or gooseneck barnacles, are filter-feeding crustaceans that live attached to hard surfaces of rocks and flotsam in the ocean intertidal zone. Goose barnacles formerly made up the taxonomic order Ped ...

s that live as

parasite Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has ...

s on various shark

hosts A host is a person responsible for guests at an event or for providing hospitality during it. Host may also refer to: Places *Host, Pennsylvania, a village in Berks County People *Jim Host (born 1937), American businessman *Michel Host ( ...

Taxonomy

The genus ''Anelasma'' contains a single species, ''Anelasma squalicola''. The nominal species, however, has a very broad distribution and may in fact be a

species complex In biology, a species complex is a group of closely related organisms that are so similar in appearance and other features that the boundaries between them are often unclear. The taxa in the complex may be able to hybridize readily with each oth ...

that contain several

undescribed species In taxonomy, an undescribed taxon is a taxon (for example, a species) that has been discovered, but not yet formally described and named. The various Nomenclature Codes specify the requirements for a new taxon to be validly described and named. U ...

. It has been suggested that ''Anelasma'' diverged from the ancestor it shares with its current closest relatives (the free-living, suspension-feeding species in the genera ''

Capitulum capitulum (plural capitula) may refer to: *the Latin word for chapter ** an index or list of chapters at the head of a gospel manuscript ** a short reading in the Liturgy of the Hours *** derived from which, it is the Latin for the assembly known ...

'' and '' Pollicipes'') a long time ago. The species may represent the only remaining representative of a previously more numerous clade that made the evolutionary transition from filter-feeding to parasitism.

Description

left, Velvet belly lanternshark with ''Anelasma'' This barnacle reaches a length of approximately 25 mm. Unlike most barnacles, it has no shell; the outermost integument is its tough, purplish-black mantle, without any calcareous plates. The body protrudes from the skin of its host and is usually encountered in pairs. The

cirri Giovanni Battista Cirri (1 October 1724 – 11 June 1808) was an Italian cellist and composer in the 18th century. Biography Cirri was born in Forlì in the Emilia-Romagna Region of Italy. He had his first musical training with his brother ...

, normally used by barnacles for filtering food items out of the water, are

vestigial Vestigiality is the retention, during the process of evolution, of genetically determined structures or attributes that have lost some or all of the ancestral function in a given species. Assessment of the vestigiality must generally rely on co ...

, being small and unbranched, and have lost their feeding function. Nutrition is instead extracted from the host through hidden tendrils that extend downwards from the base.

Distribution

The species is widespread in deeper waters (samples off South Africa have been obtained from ~650 m) and occurs on a variety of shark species. Records are known from cold waters off Greenland, Britain, New Zealand, Chile and South Africa, as well as warmer waters off Spain, the Canary Islands, Australia, and in the Gulf of Mexico.

Ecology

''Anelasma'' are mesoparasitic barnacles that can be found attached to several species of deep-sea squaloid sharks, including at least

black dogfish The black dogfish (''Centroscyllium fabricii'') is a species of dogfish shark in the family Etmopteridae. It is common over the outer continental shelf and continental slope at depths of . Females generally inhabit deeper water than males, and ...

(''Centroscyllium fabricii''), combtooth dogfish (''Centroscyllium nigrum''),

velvet belly lanternshark The velvet belly lanternshark (or simply velvet belly) (''Etmopterus spinax'') is a species of dogfish shark in the family Etmopteridae. One of the most common deepwater sharks in the northeastern Atlantic Ocean, the velvet belly is found from Ic ...

(''Etmopterus spinax''),

fringefin lanternshark The fringefin lanternshark (''Etmopterus schultzi'') is a shark of the family Etmopteridae found in the western central Atlantic from Texas to Florida, northern Gulf of Mexico, and Mexico. It is endemic to this area. It is a deep water shark and ...

(''E. schultzi''), great lanternshark (''E. princeps''),

brown lanternshark The brown lanternshark or bristled lanternshark (''Etmopterus unicolor'') is a little-known species of deep-sea dogfish shark in the family Etmopteridae. It is found off Japan and New Zealand, and possibly also South Africa and Australia, typi ...

(''E. unicolor''), and southern lanternshark (''E. granulosus''). ''Anelasma'' are partially embedded in the flesh of the host, and seem to retard sexual development of their hosts, apparently

castrating Castration is any action, surgical, chemical, or otherwise, by which an individual loses use of the testicles: the male gonad. Surgical castration is bilateral orchiectomy (excision of both testicles), while chemical castration uses pharmaceu ...

them.

References

http://marinespecies.org/aphia.php?p=taxdetails&id=106093

External links

* {{Taxonbar, from=Q15896140 Barnacles Monotypic crustacean genera Parasitic crustaceans Taxa named by Charles Darwin