Anomura is a group of decapod

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...

 crustacean

Crustacean

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, including 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 and others. Although the names of many anomurans includes the word crab, all true 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...

s are in the sister group to the Anomura, the Brachyura

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...

 (the two groups together form the clade

Clade

A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...

 Meiura).

Description

The name Anomala reflects the unusual variety of forms in this group; whereas all crabs share some obvious similarities, the various groups of anomurans are quite dissimilar. The name Anomura derives from an old classification in which reptant decapods were divided into Macrura (long-tailed), Brachyura (short-tailed) and Anomura (differently-tailed).

As decapods (meaning ten-legged), anomurans have ten pereiopods, but the last pair of these is often hidden inside the gill chamber (under the 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...

) and is used for keeping the gills clean. Since this arrangement is very rare in true crabs

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...

 (only in the small family Hexapodidae

Hexapodidae

Hexapodidae is a family of crabs, the only family in the superfamily Hexapodoidea. It has traditionally been treated as a subfamily of the family Goneplacidae, and was originally described as a subfamily of Pinnotheridae...

), a "crab" with only eight pereiopods is generally an anomuran.

Classification

The Infraorder Anomura is divided into eight superfamilies:

Superfamily	Members	Families	Photo
Aegloidea	Aegla	Aeglidae Aeglidae Aeglidae is a family of freshwater crustaceans currently restricted to South America. They are the only anomurans to be found in fresh water except for a single hermit crab species, Clibanarius fonticola, on Espiritu Santo island, Vanuatu...
† Eocarcinoidea Eocarcinoidea Eocarcinoidea is a family of fossil decapod crustaceans. Formerly thought to be the earliest true crabs, they are now thought to be the oldest members of the Anomura. Two species are included, each in its own family: Eocarcinus praecursor and Platykotta akaina ....	† Eocarcinus Eocarcinus Eocarcinus praecursor is a Jurassic species of decapod crustacean, sufficiently distinct from its relatives to be placed in its own family... † Platykotta Platykotta Platykotta akaina is a species of decapod crustacean from the Triassic of the United Arab Emirates. It is the oldest known fossil from the infraorder Anomura, and is most closely related to Eocarcinus praecursor.-Stratigraphy:The holotype of P...	† Eocarcinidae Eocarcinus Eocarcinus praecursor is a Jurassic species of decapod crustacean, sufficiently distinct from its relatives to be placed in its own family... † Platykottidae Platykotta Platykotta akaina is a species of decapod crustacean from the Triassic of the United Arab Emirates. It is the oldest known fossil from the infraorder Anomura, and is most closely related to Eocarcinus praecursor.-Stratigraphy:The holotype of P...
Galatheoidea Galatheoidea Galatheoidea is a superfamily of decapod crustaceans comprising some squat lobsters and the porcelain crabs. Two other families of squat lobsters, Chirostylidae and Kiwaidae, are not closely related to the members of Galatheoidea, and are now placed in other superfamilies...	squat lobster Squat lobster Squat lobsters are decapod crustaceans of the families Galatheidae, Chirostylidae and Kiwaidae, including the common genera Galathea and Munida. They are not lobsters at all, but are more closely related to porcelain crabs, hermit crabs and then, more distantly, true crabs... s porcelain crab Porcelain crab Porcelain crabs are decapod crustaceans in the widespread family Porcellanidae, which superficially resemble true crabs. They are typically less than wide, and have flattened bodies as an adaptation for living in rock crevices... s	Chirostylidae Galatheidae Porcellanidae Porcelain crab Porcelain crabs are decapod crustaceans in the widespread family Porcellanidae, which superficially resemble true crabs. They are typically less than wide, and have flattened bodies as an adaptation for living in rock crevices... † Retrorsichelidae	Munidopsis serricornis Munidopsis serricornis Munidopsis serricornis is a species of squat lobster. It is widely distributed in the world's oceans, being found in the eastern Atlantic Ocean , the western Atlantic Ocean , and the Indo-Pacific... (Galatheidae)
Hippoidea Hippoidea Hippoidea is a superfamily of decapod crustaceans known as sand crabs or mole crabs.-Ecology:Hippoids are adapted to burrowing into sandy beaches, a habit they share with raninid crabs, and the parallel evolution of the two groups is striking...	mole crabs sand crab Sand crab The common term sand crab can refer to various species of crustacean:* Crustacea of the superfamily Hippoidea, often known as mole crabs* Crabs of the genus Ocypode, also commonly known as ghost crabs... s	Albuneidae Albuneidae Albuneidae is a little-known family of specialized burrowing sand crabs. There are 50 extant species as well as nine fossil species that have been described. Fossil specimens have been described from the Cretaceous, Miocene and Oligocene.... Blepharipodidae Hippidae Hippidae Hippidae is a family of decapod crustaceans, commonly known as "mole crabs" or "sand crabs". They are closely related to the family Albuneidae, with which they are usually joined in the superfamily Hippoidea. The family Hippidae comprises the three genera Emerita, Hippa and Mastigochirus...	Blepharipoda occidentalis Blepharipoda occidentalis Blepharipoda occidentalis, the spiny sand crab or spiny mole crab, is a species of sand crab or mole crab which lives in the eastern Pacific Ocean, from Central California to Baja California. It is oval in shape, growing up to long and wide. It lives on sandy beaches up to under water, and feeds... (Blepharipodidae)
Kiwaoidea Kiwa hirsuta Kiwa hirsuta is a crustacean discovered in 2005 in the South Pacific Ocean. This decapod, which is approximately long, is notable for the quantity of silky blond setae covering its pereiopods . Its discoverers dubbed it the "yeti lobster" or "yeti crab."-Identification:K...	Kiwa hirsuta Kiwa hirsuta Kiwa hirsuta is a crustacean discovered in 2005 in the South Pacific Ocean. This decapod, which is approximately long, is notable for the quantity of silky blond setae covering its pereiopods . Its discoverers dubbed it the "yeti lobster" or "yeti crab."-Identification:K...	Kiwaidae Kiwa hirsuta Kiwa hirsuta is a crustacean discovered in 2005 in the South Pacific Ocean. This decapod, which is approximately long, is notable for the quantity of silky blond setae covering its pereiopods . Its discoverers dubbed it the "yeti lobster" or "yeti crab."-Identification:K...
Lithodoidea	king crab King crab King crabs, also called stone crabs, are a superfamily of crab-like decapod crustaceans chiefly found in cold seas. Because of their large size and the taste of their meat, many species are widely caught and sold as food, the most common being the red king crab, Paralithodes camtschaticus.King... s	Hapalogastridae Hapalogastridae Hapalogastridae is a family of decapod crustaceans, containing the following species:*Acantholithodes Holmes, 1895**Acantholithodes hispidus *Dermaturus Brandt, 1850**Dermaturus mandtii Brandt, 1850 — wrinkled crab... Lithodidae	Lithodes santolla (Lithodidae King crab King crabs, also called stone crabs, are a superfamily of crab-like decapod crustaceans chiefly found in cold seas. Because of their large size and the taste of their meat, many species are widely caught and sold as food, the most common being the red king crab, Paralithodes camtschaticus.King... )
Lomisoidea	hairy stone crab Hairy stone crab The hairy stone crab, Lomis hirta, is a crab-like crustacean that lives in the littoral zone of southern Australia from Bunbury, Western Australia to the Bass Strait. It is the only species in its family...	Lomisidae
Paguroidea 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:...	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 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...	Coenobitidae Coenobitidae Coenobitidae are a family of hermit crabs, widely known for their terrestrial habits. There are 17 species in two genera:*Coenobita Latreille, 1829*Coenobita brevimanus Dana, 1852*Coenobita carnescens Dana, 1851... Diogenidae Paguridae Paguridae Paguridae is a family of hermit crabs of the order Decapoda. It contains 542 species in over 70 genera:*Acanthopagurus de Saint Laurent, 1968*Agaricochirus McLaughlin, 1981*Alainopaguroides McLaughlin, 1997... Parapaguridae Parapaguridae Parapaguridae is a family of terrestrial hermit crabs. They have gill chambers that function as lungs. Some genera, such as Bivalvopagurus and Tylaspis, do not inhabit shells... Pylochelidae Pylochelidae Pylochelidae is 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, at depths of up to... Pylojacquesidae Pylojacquesidae Pylojacquesidae is a small family of hermit crabs, comprising only two species in two genera. The family was erected in 2001, after two specimens at at the were recognised as being quite distinct from other described hermit crabs...	Coenobita clypeatus (Coenobitidae Coenobitidae Coenobitidae are a family of hermit crabs, widely known for their terrestrial habits. There are 17 species in two genera:*Coenobita Latreille, 1829*Coenobita brevimanus Dana, 1852*Coenobita carnescens Dana, 1851... )

The oldest fossil

Fossil

Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

 attributed to Anomura is Platykotta

Platykotta

Platykotta akaina is a species of decapod crustacean from the Triassic of the United Arab Emirates. It is the oldest known fossil from the infraorder Anomura, and is most closely related to Eocarcinus praecursor.-Stratigraphy:The holotype of P...

, from the Norian

Norian

The Norian is a division of the Triassic geological period. It has the rank of an age or stage . The Norian lasted from 216.5 ± 2.0 to 203.6 ± 1.5 million years ago. It was preceded by the Carnian and succeeded by the Rhaetian.-Stratigraphic definitions:The Norian was named after the Noric Alps in...

–Rhaetian

Rhaetian

The Rhaetian is in geochronology the latest age of the Triassic period or in chronostratigraphy the uppermost stage of the Triassic system. It lasted from 203.6 ± 1.5 to 199.6 ± 0.6 million years ago...

 of the United Arab Emirates

United Arab Emirates

The United Arab Emirates, abbreviated as the UAE, or shortened to "the Emirates", is a state situated in the southeast of the Arabian Peninsula in Western Asia on the Persian Gulf, bordering Oman, and Saudi Arabia, and sharing sea borders with Iraq, Kuwait, Bahrain, Qatar, and Iran.The UAE is a...

.

Kiwa hirsuta

Kiwa hirsuta

Kiwa hirsuta is a crustacean discovered in 2005 in the South Pacific Ocean. This decapod, which is approximately long, is notable for the quantity of silky blond setae covering its pereiopods . Its discoverers dubbed it the "yeti lobster" or "yeti crab."-Identification:K...

was discovered in 2005 on a deep sea hydrothermal vent

Hydrothermal vent

A hydrothermal vent is a fissure in a planet's surface from which geothermally heated water issues. Hydrothermal vents are commonly found near volcanically active places, areas where tectonic plates are moving apart, ocean basins, and hotspots. Hydrothermal vents exist because the earth is both...

, and placed in a new family.