Pylochelidae
Encyclopedia
Pylochelidae is a family
of hermit crab
s. Its members are commonly called the symmetrical hermit crabs. They live in all the world's oceans, except the Arctic
and the Antarctic
, at depths of up to 2000 metres (6,561.7 ft). Due to their cryptic nature
and relative scarcity, only around 60 specimens had been collected before 1987, when a monograph
was published detailing a further 400.
s, pylochelid hermit crabs are not markedly asymmetrical, with a straight body and equal numbers of appendage
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
, when describing the first species, to consider it to represent a transition between hermit crabs and "Macrura" (long-tailed decapods
, such as lobster
s and shrimp
). Correspondingly, pylochelid hermit crabs do not usually inhabit gastropod shell
s, but instead withdraw into decayed pieces of wood
, stones, tusk shell
s (especially Dentaliidae
), living sponges, pieces of bamboo
or mangrove
s. Their claw
s are often adapted
to form an operculum, which closes off the entrance to their home.
, with only four species being found in the western Atlantic Ocean
and Caribbean Sea
(Cheiroplatea scutata, Pylocheles agassizii, Bathycheles cubensis and Mixtopagurus paradoxus). There is also a great range in water depths inhabited by pylochelid hermit crabs, from 100 metres (328.1 ft) to 2200 m (7,217.8 ft), with most living between 200 metre deep.
Some fossil
ised carapace
s from the Late Jurassic
are thought to represent members of the Pylochelidae.
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
of hermit crab
Hermit crab
Hermit crabs are decapod crustaceans of the superfamily Paguroidea. Most of the 1100 species possess an asymmetrical abdomen which is concealed in an empty gastropod shell that is carried around by the hermit crab.-Description:...
s. Its members are commonly called the symmetrical hermit crabs. They live in all the world's oceans, except the Arctic
Arctic
The Arctic is a region located at the northern-most part of the Earth. The Arctic consists of the Arctic Ocean and parts of Canada, Russia, Greenland, the United States, Norway, Sweden, Finland, and Iceland. The Arctic region consists of a vast, ice-covered ocean, surrounded by treeless permafrost...
and the Antarctic
Antarctic
The Antarctic is the region around the Earth's South Pole, opposite the Arctic region around the North Pole. The Antarctic comprises the continent of Antarctica and the ice shelves, waters and island territories in the Southern Ocean situated south of the Antarctic Convergence...
, at depths of up to 2000 metres (6,561.7 ft). Due to their cryptic nature
Crypsis
In ecology, crypsis is the ability of an organism to avoid observation or detection by other organisms. It may be either a predation strategy or an antipredator adaptation, and methods include camouflage, nocturnality, subterranean lifestyle, transparency, and mimicry...
and relative scarcity, only around 60 specimens had been collected before 1987, when a monograph
Monograph
A monograph is a work of writing upon a single subject, usually by a single author.It is often a scholarly essay or learned treatise, and may be released in the manner of a book or journal article. It is by definition a single document that forms a complete text in itself...
was published detailing a further 400.
Description
Unlike other hermit crabHermit crab
Hermit crabs are decapod crustaceans of the superfamily Paguroidea. Most of the 1100 species possess an asymmetrical abdomen which is concealed in an empty gastropod shell that is carried around by the hermit crab.-Description:...
s, pylochelid hermit crabs are not markedly asymmetrical, with a straight body and equal numbers of appendage
Appendage
In invertebrate biology, an appendage is an external body part, or natural prolongation, that protrudes from an organism's body . It is a general term that covers any of the homologous body parts that may extend from a body segment...
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 J. Miers
Edward John Miers F.Z.S. F.L.S. was a British zoologist and curator of the crustacean collection at the Natural History Museum in London...
, when describing the first species, to consider it to represent a transition between hermit crabs and "Macrura" (long-tailed decapods
Decapoda
The decapods or Decapoda are an order of crustaceans within the class Malacostraca, including many familiar groups, such as crayfish, crabs, lobsters, prawns and shrimp. Most decapods are scavengers. It is estimated that the order contains nearly 15,000 species in around 2,700 genera, with...
, such as lobster
Lobster
Clawed lobsters comprise a family of large marine crustaceans. Highly prized as seafood, lobsters are economically important, and are often one of the most profitable commodities in coastal areas they populate.Though several groups of crustaceans are known as lobsters, the clawed lobsters are most...
s and shrimp
Shrimp
Shrimp are swimming, decapod crustaceans classified in the infraorder Caridea, found widely around the world in both fresh and salt water. Adult shrimp are filter feeding benthic animals living close to the bottom. They can live in schools and can swim rapidly backwards. Shrimp are an important...
). Correspondingly, pylochelid hermit crabs do not usually inhabit gastropod shell
Gastropod shell
The gastropod shell is a shell which is part of the body of a gastropod or snail, one kind of mollusc. The gastropod shell is an external skeleton or exoskeleton, which serves not only for muscle attachment, but also for protection from predators and from mechanical damage...
s, but instead withdraw into decayed pieces of wood
Wood
Wood is a hard, fibrous tissue found in many trees. It has been used for hundreds of thousands of years for both fuel and as a construction material. It is an organic material, a natural composite of cellulose fibers embedded in a matrix of lignin which resists compression...
, stones, tusk shell
Tusk shell
The tusk shells or scaphopods are a class of shelled marine mollusks. The scientific name of this class is Scaphopoda, meaning "shovel-footed". Shells of species within this class range from about 0.5 to 15 cm in length...
s (especially Dentaliidae
Dentaliidae
Dentaliidae is a family of tusk shells in the order Dentaliida.-Genera:* Antalis H. & A. Adams, 1854 * Coccodentalium Sacco, 1896 * Compressidentalium Habe, 1963 * Dentalium Linnaeus, 1758 * Eudentalium Cotton & Godfrey, 1933...
), living sponges, pieces of bamboo
Bamboo
Bamboo is a group of perennial evergreens in the true grass family Poaceae, subfamily Bambusoideae, tribe Bambuseae. Giant bamboos are the largest members of the grass family....
or mangrove
Mangrove
Mangroves are various kinds of trees up to medium height and shrubs that grow in saline coastal sediment habitats in the tropics and subtropics – mainly between latitudes N and S...
s. Their claw
Claw
A claw is a curved, pointed appendage, found at the end of a toe or finger in most mammals, birds, and some reptiles. However, the word "claw" is also often used in reference to an invertebrate. Somewhat similar fine hooked structures are found in arthropods such as beetles and spiders, at the end...
s are often adapted
Adaptation
An adaptation in biology is a trait with a current functional role in the life history of an organism that is maintained and evolved by means of natural selection. An adaptation refers to both the current state of being adapted and to the dynamic evolutionary process that leads to the adaptation....
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-PacificIndo-Pacific
The Indo-Pacific is a biogeographic region of the Earth's seas, comprising the tropical waters of the Indian Ocean, the western and central Pacific Ocean, and the seas connecting the two in the general area of Indonesia...
, with only four species being found in the western Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
and Caribbean Sea
Caribbean Sea
The Caribbean Sea is a sea of the Atlantic Ocean located in the tropics of the Western hemisphere. It is bounded by Mexico and Central America to the west and southwest, to the north by the Greater Antilles, and to the east by the Lesser Antilles....
(Cheiroplatea scutata, Pylocheles agassizii, Bathycheles cubensis and Mixtopagurus paradoxus). There is also a great range in water depths inhabited by pylochelid hermit crabs, from 100 metres (328.1 ft) to 2200 m (7,217.8 ft), with most living between 200 metre deep.
Genera
The family contains 41 species in 10 genera:- Bathycheles — 6 species
- Cancellocheles — 1 species
- Cheiroplatea — 6 species
- Forestocheles — 1 species
- Mixtopagurus — 1 species
- Parapylocheles — 1 species
- Pomatocheles — 3 species
- Pylocheles — 2 species
- Trizocheles — 18 species
- Xylocheles — 2 species
Some fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
ised 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...
s from the Late Jurassic
Late Jurassic
The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 161.2 ± 4.0 to 145.5 ± 4.0 million years ago , which is preserved in Upper Jurassic strata. In European lithostratigraphy, the name "Malm" indicates rocks of Late Jurassic age...
are thought to represent members of the Pylochelidae.