The Pylochelidae are a family of hermit crabs. Its members are commonly called the 'symmetrical hermit crabs'. They live in all the world's oceans, except the Arctic and the

Antarctic The Antarctic ( or , American English also or ; commonly ) is a polar region around Earth's South Pole, opposite the Arctic region around the North Pole. The Antarctic comprises the continent of Antarctica, the Kerguelen Plateau and other ...

, at depths of . Due to their cryptic nature and relative scarcity, only around 60 specimens had been collected before 1987, when a

monograph A monograph is a specialist work of writing (in contrast to reference works) or exhibition on a single subject or an aspect of a subject, often by a single author or artist, and usually on a scholarly subject. In library cataloging, ''monograph ...

was published detailing a further 400. Pylochelidae (MNHN-IU-2013-2380)

Description

Unlike other hermit crabs, pylochelid hermit crabs are not markedly asymmetrical, with a straight body and equal numbers of

appendage An appendage (or outgrowth) is an external body part, or natural prolongation, that protrudes from an organism's body. In arthropods, an appendage refers to any of the homologous body parts that may extend from a body segment, including anten ...

s on both sides. This characteristic, together with the partial calcification of the abdomen (which is soft in other hermit crabs) led

Edward J. Miers Edward John Miers Zoological Society of London, FZS Fellow of the Linnean Society, FLS (1851– 15 October 1930) was a British zoologist and curator of the crustacean collection at the Natural History Museum, London, Natural History Museum in Lond ...

, when describing the first species, to consider it to represent a transition between hermit crabs and "Macrura" (long-tailed decapods, such as

lobster Lobsters are a family (biology), family (Nephropidae, Synonym (taxonomy), synonym Homaridae) of marine crustaceans. They have long bodies with muscular tails and live in crevices or burrows on the sea floor. Three of their five pairs of legs ...

s and

shrimp Shrimp are crustaceans (a form of shellfish) with elongated bodies and a primarily swimming mode of locomotion – most commonly Caridea and Dendrobranchiata of the decapod order, although some crustaceans outside of this order are refer ...

). Correspondingly, pylochelid hermit crabs do not usually inhabit gastropod shells, but instead withdraw into decayed pieces of wood, stones, tusk shells (especially

Dentaliidae Dentaliidae is a family of relatively large tusk shells, scaphopod mollusks in the order Dentaliida. Genera * '' Antalis'' H. & A. Adams, 1854 * '' Coccodentalium'' Sacco, 1896 * '' Compressidentalium'' Habe, 1963 * '' Dentalium'' ...

), living sponges, pieces of bamboo or mangroves. Their claws are often adapted to form an operculum, which closes off the entrance to their home.

Distribution

Although the family as a whole has a global distribution, diversity is concentrated in the

Indo-Pacific The Indo-Pacific is a vast biogeographic region of Earth. In a narrow sense, sometimes known as the Indo-West Pacific or Indo-Pacific Asia, it comprises the tropical waters of the Indian Ocean, the western and central Pacific Ocean, and the ...

, with only four species being found in the western Atlantic Ocean and Caribbean Sea (''

Cheiroplatea scutata ''Cheiroplatea'' is a genus of hermit crabs within the family Pylochelidae. Species * ''Cheiroplatea cenobita'' Spence Bate, 1888 * ''Cheiroplatea laticauda'' Boas, 1926 * ''Cheiroplatea mitoi'' Miyake, 1978 * ''Cheiroplatea pumicicola'' Fore ...

'', '' Pylocheles agassizii'', '' Bathycheles cubensis'' and '' Mixtopagurus paradoxus''). Pylochelid hermit crabs inhabit a great range in water depths, from , with most living between deep.

Genera

The family contains 41 species in 10 genera: *'' Bathycheles'' – six species *'' Cancellocheles'' – one species *''

Cheiroplatea ''Cheiroplatea'' is a genus of hermit crabs within the family Pylochelidae The Pylochelidae are a family of hermit crabs. Its members are commonly called the 'symmetrical hermit crabs'. They live in all the world's oceans, except the Arctic an ...

'' – six species *† ''

Cretatrizocheles ''Cretatrizocheles olazagutiensis'' is an extinct hermit crab which existed during the Albian or Cenomanian of what is now Spain , image_flag = Bandera de España.svg , image_coat = Escudo de España (mazonado).svg , n ...

'' – one species *'' Forestocheles'' – one species *'' Mixtopagurus'' – one species *'' Pomatocheles'' – three species *'' Pylocheles'' – two species *'' Trizocheles'' – 18 species *'' Xylocheles'' – two species

References

External links

* {{Taxonbar, from=Q3411224 Hermit crabs Extant Late Jurassic first appearances Decapod families