Anomura
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Anomura (sometimes Anomala) are 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 Meiura).
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) and is used for keeping the gills clean. Since this arrangement is never found in true crabs, a "crab" with only eight pereiopods must be an Anomuran.
The Infraorder Anomura is divided into four superfamilies:
- Lomisoidea - contains a single family, which contains a single species - Lomis hirta, the Hairy Stone Crab
- Hippoidea - containing the two families of mole crabs, Hippidae and Albuneidae
- Galatheoidea - containing squat lobsters and related animals in five families: Galatheidae (squat lobsters), Chirostylidae (squat lobsters), Porcellanidae (porcelain crabs), Aeglidae (a small group of South American freshwater anomurans with no common name in English), and Kiwaidae, containing the newly-discovered Kiwa hirsuta.
- Paguroidea - hermit crabs and their relatives: Coenobitidae, Diogenidae, Paguridae, Parapaguridae, Pylochelidae, and the king crabs or stone crabs in the Lithodidae)
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