Anomura (sometimes Anomala) is a group of decapod crustaceans, including hermit crabs and others. Although the names of many anomurans includes the word crab, all true crabs are in the sister group to the Anomura, the Brachyura (the two groups together form the clade ).1]
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.[2] 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).
The group has been moulded by several instances of carcinisation ? the development of a crab-like body form.[3] Thus, the king crabs (Lithodidae), porcelain crabs (Porcellanidae) and hairy stone crab (Lomisidae) are all separate instances of carcinisation.[3]
As decapods (meaning ten-legged), anomurans have ten pereiopods, but the last pair of these is often reduced in size, and hidden inside the gill chamber (under the carapace) to be used for cleaning the gills.[2] Since this arrangement is very rare in true crabs (for example, the small family Hexapodidae),[4] a "crab" with only eight visible pereiopods is generally an anomuran.[2]
There is wide acceptance from morphological and molecular data
that Anomura and Brachyura (true crabs) are sister taxa, together making up the clade Meiura.[3]
The infraorder Anomura is divided into eight superfamilies:[5][6]
The oldest fossil attributed to Anomura is Platykotta, from the Norian?Rhaetian of the United Arab Emirates.[6]
Kiwa hirsuta was discovered in 2005 on a deep sea hydrothermal vent, and placed in a new family.[7] A second species, Kiwa puravida, was described in 2011.[8]
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. [more]
Chirostylidae
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. They are distributed worldwide in the oceans, and occur from near the surface to deep sea hydrothermal vents. There are currently 870 described species. [more]
Coenobitidae
Coenobitidae are a family of hermit crabs, widely known for their terrestrial habits. There are 17 species in two genera: [more]
Diogenidae
Diogenidae is a family of hermit crabs, sometimes known as "left-handed hermit crabs" because in contrast to most other hermit crabs, it is the left chela (claw) that is enlarged instead of the right. It comprises 429 extant species, and a further 46 extinct species, making it the second largest family of marine hermit crabs, after Paguridae. [more]
Galatheidae
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. They are distributed worldwide in the oceans, and occur from near the surface to deep sea hydrothermal vents. There are currently 870 described species. [more]
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 . They burrow into sand, and are found throughout the world, except the Arctic and Antarctic. [more]
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. [more]
Paguridae is a family of hermit crabs of the order Decapoda. It contains 542 species in over 70 genera: [more]
Parapaguridae
Parapaguridae is a family of terrestrial hermit crabs. They have gill chambers that function as lungs. Some genera, such as and Tylaspis, do not inhabit shells. The following genera are included: [more]
Porcelain crabs are decapod crustaceans in the widespread family Porcellanidae, which superficially resemble true crabs. They are typically less than 15 mm (0.6 in) wide, and have flattened bodies as an adaptation for living in rock crevices. They are delicate, readily losing limbs when attacked, and use their large claws for maintaining territories. [more]
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 2,000 metres (6,600 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. [more]
At least 22 species and subspecies belong to the Family Pylochelidae.
More info about the Family Pylochelidae may be found here.
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