''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 Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found elsew ...

Southern California Southern California (commonly shortened to SoCal) is a geographic and Cultural area, cultural region that generally comprises the southern portion of the U.S. state of California. It includes the Los Angeles metropolitan area, the second most po ...

. 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 The International Union for Conservation of Nature (IUCN) Red List of Threatened Species, also known as the IUCN Red List or Red Data Book, founded in 1964, is the world's most comprehensive inventory of the global conservation status of biol ...

in 1996.

Description

''Parapinnixa affinis'' is similar to other

pea crab The pea crab, ''Pinnotheres pisum'', is a small crab in the family Pinnotheridae that lives as a parasite in oysters, clams, mussels, and other species of bivalves. Description Pea crabs are small crustaceans about the size of a pea or dime, wit ...

s 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 Albinism is the congenital absence of melanin in an animal or plant resulting in white hair, feathers, scales and skin and pink or blue eyes. Individuals with the condition are referred to as albino. Varied use and interpretation of the term ...

Distribution

''Parapinnixa affinis'' appears to be

, having been recorded from San Pedro, Anaheim Landing, Newport Bay and

San Diego San Diego ( , ; ) is a city on the Pacific Ocean coast of Southern California located immediately adjacent to the Mexico–United States border. With a 2020 population of 1,386,932, it is the List of United States cities by population, eigh ...

. It was once recorded from

Siberia Siberia ( ; rus, Сибирь, r=Sibir', p=sʲɪˈbʲirʲ, a=Ru-Сибирь.ogg) is an extensive geographical region, constituting all of North Asia, from the Ural Mountains in the west to the Pacific Ocean in the east. It has been a part of ...

, but this record is doubtful.

Conservation and ecology

''Parapinnixa affinis'' was one of only two marine

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 ...

s 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 The coconut crab (''Birgus latro'') is a species of terrestrial hermit crab, also known as the robber crab or palm thief. It is the largest terrestrial arthropod in the world, with a weight of up to . It can grow to up to in width from the tip ...

. 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

bryozoa Bryozoa (also known as the Polyzoa, Ectoprocta or commonly as moss animals) are a phylum of simple, aquatic invertebrate animals, nearly all living in sedentary colonies. Typically about long, they have a special feeding structure called a l ...

n 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 In biology, a type is a particular wiktionary:en:specimen, specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally attached. In other words, a type is an example that serves to a ...

was a single female, collected in July 1895 from Dead Man's Island,

San Pedro, California San Pedro ( ; Spanish: " St. Peter") is a neighborhood within the City of Los Angeles, California. Formerly a separate city, it consolidated with Los Angeles in 1909. The Port of Los Angeles, a major international seaport, is partially located wi ...

(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 The University of California (UC) is a public land-grant research university system in the U.S. state of California. The system is composed of the campuses at Berkeley, Davis, Irvine, Los Angeles, Merced, Riverside, San Diego, San Francisco, ...

. ''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