''Hemioniscus balani'', a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

of isopod

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group can ...

, is a widespread parasitic castrator of barnacle in the northern

Atlantic Ocean The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe ...

. Its

range Range may refer to: Geography * Range (geographic), a chain of hills or mountains; a somewhat linear, complex mountainous or hilly area (cordillera, sierra) ** Mountain range, a group of mountains bordered by lowlands * Range, a term used to i ...

extends from

Norway Norway, officially the Kingdom of Norway, is a Nordic country in Northern Europe, the mainland territory of which comprises the western and northernmost portion of the Scandinavian Peninsula. The remote Arctic island of Jan Mayen and the ...

to the Atlantic coast of

France France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of overseas regions and territories in the Americas and the Atlantic, Pacific and Indian Oceans. Its metropolitan area ...

, and as far west as

Massachusetts Massachusetts (Massachusett: ''Muhsachuweesut Massachusett_writing_systems.html" ;"title="nowiki/> məhswatʃəwiːsət.html" ;"title="Massachusett writing systems">məhswatʃəwiːsət">Massachusett writing systems">məhswatʃəwiːsət'' En ...

. It is also commonly found on the Pacific coast of North America; it is not known if the Pacific and Atlantic populations are the same species, or if the Pacific population exists following human-assisted introduction.

Life history

''H. balani'' parasitically castrates adults of several species of barnacles, including '' Semibalanus balanoides'', ''

Chthamalus fissus ''Chthamalus fissus'' is a species of star barnacle in the family Chthamalidae. References External links * Sessilia {{crustacean-stub Crustaceans described in 1854 ...

'', '' Chthamalus dalli'', and ''

Balanus glandula ''Balanus glandula'' (North American Acorn Barnacle, Common Acorn Barnacle) is one of the most common barnacle species on the Pacific coast of North America, distributed from the U.S. state of Alaska to Bahía de San Quintín near San Quintín, ...

''. Rarely does more than one ''H. balani'' parasitize the same host, but under conditions of heavy infestation, a single barnacle may contain as many as seven ''H. balani'' individuals. Both the isopod parasite and its barnacle host are hermaphroditic crustaceans with a free-swimming larva and a sessile adult. ''H. balani'' is a

protandrous Sequential hermaphroditism (called dichogamy in botany) is a type of hermaphroditism that occurs in many fish, gastropods, and plants. Sequential hermaphroditism occurs when the individual changes its sex at some point in its life. In particular, ...

hermaphrodite that develops into a female only after attaching to its adult host. While in its male swimming form, it resembles a typical isopod with antennae, jointed limbs, and a segmented exoskeleton. When fully mature, the adult female form of ''H. balani'' is reduced to a bloated, star-shaped egg sac, up to 8 mm in length inhabiting the mantle cavity of its barnacle host. The barnacle host species are simultaneous hermaphrodites, with both male and female gonads in each adult. ''H. balani'' feeds on its host's ovarian fluid, so the barnacle loses female reproductive ability, but can still produce sperm.

References

{{Taxonbar, from=Q3862741 Cymothoida Crustaceans of the Atlantic Ocean Crustaceans described in 1866 Parasites of crustaceans Parasitic crustaceans