| Anomura Temporal range: Norian–Recent |
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|---|---|
| The hermit crab Dardanus megistos | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Subphylum: | Crustacea |
| Class: | Malacostraca |
| Order: | Decapoda |
| Suborder: | Pleocyemata |
| Infraorder: | Anomura Macleay, 1838 |
| Superfamilies | |
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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 Meiura).[1]
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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 very rare in true crabs (only in the small family Hexapodidae),[2] a "crab" with only eight pereiopods is generally an anomuran.
The Infraorder Anomura is divided into eight superfamilies:[3][4]
| Superfamily | Members | Families | Photo |
|---|---|---|---|
| Aegloidea | Aegla | Aeglidae | |
| † Eocarcinoidea | † Eocarcinus † Platykotta |
† Eocarcinidae † Platykottidae |
|
| Galatheoidea | squat lobsters porcelain crabs |
Chirostylidae Galatheidae Porcellanidae † Retrorsichelidae |
Munidopsis serricornis (Galatheidae) |
| Hippoidea | mole crabs sand crabs |
Albuneidae Blepharipodidae Hippidae |
Blepharipoda occidentalis (Blepharipodidae) |
| Kiwaoidea | Kiwa hirsuta Kiwa puravida |
Kiwaidae | Kiwa puravida |
| Lithodoidea | king crabs | Hapalogastridae Lithodidae |
Lithodes santolla (Lithodidae) |
| Lomisoidea | hairy stone crab | Lomisidae | |
| Paguroidea | hermit crabs coconut crab |
Coenobitidae Diogenidae Paguridae Parapaguridae Pylochelidae Pylojacquesidae |
Coenobita clypeatus (Coenobitidae) |
The oldest fossil attributed to Anomura is Platykotta, from the Norian–Rhaetian of the United Arab Emirates.[4]
Kiwa hirsuta was discovered in 2005 on a deep sea hydrothermal vent, and placed in a new family.[5] A second species, Kiwa puravida, was described in 2011.[6]