Parapinnixa affinis
Encyclopedia
Parapinnixa affinis, the California Bay pea crab, is a species of pinnotherid
crab
endemic to Southern California
. It is a small crab that lives commensally
in the tube of a tube-dwelling worm. It was described in 1900, and is one of only two marine crustaceans to be included on the IUCN Red List
.
s of the genus Parapinnixa
, especially P. nitida. It differs from P. nitida in the proportions of its carapace
, 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 4.5 millimetre wide, with a maximum of 6 millimetre. The carapace is usually "light amber mottled with dark ochre", but 5% of crabs are albino
.
, having been recorded from San Pedro, Anaheim Landing, Newport Bay
and San Diego. It was once recorded from Siberia
, but this record is doubtful.
s to be included on the IUCN's list of endangered species
, the other being the coconut crab
.
It lives commensally
in the tubes of the polychaete worms Terebella californica and Loimia. A bryozoa
n from the family Vesiculariidae is sometimes found on the legs of P. affinis.
by Samuel Jackson Holmes
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
, San Pedro, California (now part of the Port of Los Angeles
); 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.
Pinnotheridae
Pinnotheridae is a family of pea crabs. Pea crabs are tiny soft-bodied crabs that live commensally in the mantles of certain bivalve molluscs...
crab
Crab
True crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" , or where the reduced abdomen is entirely hidden under the thorax...
endemic to Southern California
Southern California
Southern California is a megaregion, or megapolitan area, in the southern area of the U.S. state of California. Large urban areas include Greater Los Angeles and Greater San Diego. The urban area stretches along the coast from Ventura through the Southland and Inland Empire to San Diego...
. It is a small crab that lives commensally
Commensalism
In ecology, commensalism is a class of relationship between two organisms where one organism benefits but the other is neutral...
in the tube of a tube-dwelling worm. It was described in 1900, and is one of only two marine crustaceans to be included on the IUCN Red List
IUCN Red List
The IUCN Red List of Threatened Species , founded in 1963, is the world's most comprehensive inventory of the global conservation status of biological species. The International Union for Conservation of Nature is the world's main authority on the conservation status of species...
.
Description
Parapinnixa affinis is similar to other pea crabPea crab
The New Zealand pea crab, Pinnotheres novaezelandiae, is a small, parasitic crab that lives most commonly inside New Zealand green-lipped mussels. Adult females are about the size and shape of a pea, while adult males are smaller and flatter. Adult New Zealand pea crabs are completely reliant on...
s of the genus Parapinnixa
Parapinnixa
Parapinnixa is a genus of crab in the family Pinnotheridae. Originally described by Samuel Jackson Holmes as Pseudopinnixa, he published the replacement name Parapinnixa the following year, after learning of the senior homonym Pseudopinnixa Ortmann, 1894.The genus contains the following...
, especially P. nitida. It differs from P. nitida in the proportions of its carapace
Carapace
A carapace is a dorsal 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 tortoises, the underside is called the plastron.-Crustaceans:In crustaceans, the...
, 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 4.5 millimetre wide, with a maximum of 6 millimetre. The carapace is usually "light amber mottled with dark ochre", but 5% of crabs are albino
Albinism
Albinism is a congenital disorder characterized by the complete or partial absence of pigment in the skin, hair and eyes due to absence or defect of an enzyme involved in the production of melanin...
.
Distribution
Parapinnixa affinis appears to be endemic to Southern CaliforniaSouthern California
Southern California is a megaregion, or megapolitan area, in the southern area of the U.S. state of California. Large urban areas include Greater Los Angeles and Greater San Diego. The urban area stretches along the coast from Ventura through the Southland and Inland Empire to San Diego...
, having been recorded from San Pedro, Anaheim Landing, Newport Bay
Newport Beach, California
Newport Beach, incorporated in 1906, is a city in Orange County, California, south of downtown Santa Ana. The population was 85,186 at the 2010 census.The city's median family income and property values consistently place high in national rankings...
and San Diego. It was once recorded from Siberia
Siberia
Siberia is an extensive region constituting almost all of Northern Asia. Comprising the central and eastern portion of the Russian Federation, it was part of the Soviet Union from its beginning, as its predecessor states, the Tsardom of Russia and the Russian Empire, conquered it during the 16th...
, but this record is doubtful.
Conservation and ecology
Parapinnixa affinis is one of only two marine crustaceanCrustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s to be included on the IUCN's list of endangered species
Endangered species
An endangered species is a population of organisms which is at risk of becoming extinct because it is either few in numbers, or threatened by changing environmental or predation parameters...
, the other being the coconut crab
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 land-living arthropod in the world, and is probably at the upper size limit of terrestrial animals with exoskeletons in today's atmosphere at a weight of up to...
.
It lives commensally
Commensalism
In ecology, commensalism is a class of relationship between two organisms where one organism benefits but the other is neutral...
in the tubes of the polychaete worms Terebella californica and Loimia. A bryozoa
Bryozoa
The Bryozoa, also known as Ectoprocta or commonly as moss animals, are a phylum of aquatic invertebrate animals. Typically about long, they are filter feeders that sieve food particles out of the water using a retractable lophophore, a "crown" of tentacles lined with cilia...
n from the family Vesiculariidae is sometimes found on the legs of P. affinis.
Taxonomy
Parapinnixa affinis was first describedAlpha taxonomy
Alpha taxonomy is the discipline concerned with finding, describing and naming species of living or fossil organisms. This field is supported by institutions holding collections of these organisms, with relevant data, carefully curated: such institutes include natural history museums, herbaria and...
by Samuel Jackson Holmes
Samuel Jackson Holmes
Samuel Jackson Holmes was an American zoologist. He was at University of California, Berkeley. He was also a eugenicist.He was the son of Joseph Holmes and his wife Avis Folger née Taber...
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
Deadman's Island (San Pedro)
Deadman's Island was one of two islands near San Pedro, Los Angeles, California in the 19th century. The land, sometimes referenced as Dead Man's Island, Isla Del Muerto, and Reservation Point, was dredged away in 1928 as part of a harbor development effort...
, San Pedro, California (now part of the Port of Los Angeles
Port of Los Angeles
The Port of Los Angeles, also called Los Angeles Harbor and WORLDPORT L.A, is a port complex that occupies of land and water along of waterfront. The port is located on San Pedro Bay in the San Pedro neighborhood of Los Angeles, approximately south of downtown...
); it was donated to the University of California
University of California
The University of California is a public university system in the U.S. state of California. Under the California Master Plan for Higher Education, the University of California is a part of the state's three-tier public higher education system, which also includes the California State University...
. 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
Paratype
Paratype is a technical term used in the scientific naming of species and other taxa of organisms. The exact meaning of the term paratype when it is used in zoology is not the same as the meaning when it is used in botany...
in 1932.