''Parapinnixa affinis'', the California Bay pea crab, is a species of pinnotherid

crab Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (abdomen) ( el, βραχύς , translit=brachys = short, / = tail), usually hidden entirely under the thorax. They live in all the ...

endemic to Southern California. It is a small crab that lives commensally in the tube of a tube-dwelling worm. It was one of the first marine crustaceans to be included on the IUCN Red List in 1996.

Description

''Parapinnixa affinis'' is similar to other pea crabs of the genus ''

Parapinnixa ''Parapinnixa'' is a genus of crabs in the family Parapinnixidae. Originally described by Samuel Jackson Holmes as ''Pseudopinnixa'', he published the replacement name ''Parapinnixa'' the following year, after learning of the senior homonym In ...

'', especially '' P. nitida''. It differs from ''P. nitida'' in the proportions of its

carapace A carapace is a Dorsum (biology), dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tor ...

, which is more than twice as wide as long in ''P. nitida'' but less than twice as wide as long in ''P. affinis''. The carapace is approximately wide, with a maximum of . The carapace is usually "light amber mottled with dark ochre", but 5% of crabs are albino.

Distribution

''Parapinnixa affinis'' appears to be endemic to Southern California, having been recorded from San Pedro, Anaheim Landing, Newport Bay and San Diego. It was once recorded from Siberia, but this record is doubtful.

Conservation and ecology

''Parapinnixa affinis'' was one of only two marine crustaceans to be included on the IUCN's list of

endangered species An endangered species is a species that is very likely to become extinct in the near future, either worldwide or in a particular political jurisdiction. Endangered species may be at risk due to factors such as habitat loss, poaching and inv ...

in 1996, the other being the coconut crab. Many others have been added later. It lives commensally in the tubes of the

polychaete worms Polychaeta () is a paraphyletic class of generally marine annelid worms, commonly called bristle worms or polychaetes (). Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are m ...

'' Terebella californica'' and ''

Loimia ''Loimia'' is a genus of annelids belonging to the family Terebellidae. The genus has cosmopolitan distribution. Species: *''Loimia annulifilis'' *''Loimia arborea'' *''Loimia armata'' *''Loimia bandera'' *''Loimia batilla'' *''Loimia berm ...

''. A bryozoan from the family Vesiculariidae is sometimes found on the legs of ''P. affinis''.

Taxonomy

''Parapinnixa affinis'' was first described by

Samuel Jackson Holmes Samuel Jackson Holmes (March 7, 1868 – March 5, 1964California Death Records. – California Department of Health Services Office of Health Information and Research.) was an American zoologist and eugenicist. He was a professor at the Universit ...

in 1900, in his ''Synopsis of California stalk-eyed Crustacea''. The type specimen was a single female, collected in July 1895 from

Dead Man's Island ''Dead Man's Island'' is a 1996 American made-for-television mystery-thriller film starring Barbara Eden, William Shatner and featuring an ensemble cast: Roddy McDowall, Morgan Fairchild, Traci Lords, David Faustino, Christopher Atkins, Olivia ...

, San Pedro, California (now part of the

Port of Los Angeles The Port of Los Angeles is a seaport managed by the Los Angeles Harbor Department, a unit of the City of Los Angeles. It occupies of land and water with of waterfront and adjoins the separate Port of Long Beach. Promoted as "America's Port", t ...

); it was donated to the University of California. ''P. affinis'' no longer lives at the type locality, which has been made unsuitable by the accumulation of "harbor refuse and oil". No further specimens were collected for over thirty years, until one was collected in 1930, and Steve Glassell collected specimens including an allotype in 1932.

References

{{Taxonbar, from=Q3934656 Pinnotheroidea Crustaceans of the eastern Pacific Ocean Endemic fauna of California Crustaceans described in 1900 Taxonomy articles created by Polbot