Anomura
Anomura is a group of decapod crustaceans, including hermit crabs and others. Although the names of many anomurans include the word crab, all true crabs are in the sister group to the Anomura, the Brachyura.
Description
The name Anomura derives from an old classification in which reptant decapods were divided into Macrura, Brachyura and Anomura. The alternative 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 group has been moulded by several instances of carcinisation – the development of a crab-like body form. Thus, the king crabs, porcelain crabs and hairy stone crab are all separate instances of carcinisation.
As decapods, anomurans have ten pereiopods, but the last pair of these is reduced in size, and often hidden inside the gill chamber to be used for cleaning the gills. Since this arrangement is very rare in true crabs, a "crab" with only eight visible pereiopods is generally an anomuran.
There is wide acceptance from morphological and molecular data that Anomura and Brachyura are sister taxa, together making up the clade Meiura.
Classification
The infraorder Anomura contained seven extant superfamilies:| Superfamily | Members | Families | Photo |
| Aegloidea | Aegla | Aeglidae | Aegla sp. |
| Chirostyloidea | squat lobsters | Chirostylidae Eumunididae Kiwaidae | Eumunida picta |
| † Eocarcinoidea | † Eocarcinus † Platykotta | † Eocarcinidae † Platykottidae | |
| Galatheoidea | squat lobsters porcelain crabs | Galatheidae Munididae Munidopsidae Porcellanidae † Retrorsichelidae | Munidopsis serricornis |
| Hippoidea | mole crabs or sand crabs | Albuneidae Blepharipodidae Hippidae | Blepharipoda occidentalis |
| Lithodoidea | king crabs | Hapalogastridae Lithodidae | Lithodes santolla |
| Lomisoidea | hairy stone crab | Lomisidae | |
| Paguroidea | hermit crabs coconut crab | Coenobitidae Diogenidae Paguridae Parapaguridae Parapylochelidae Pylochelidae Pylojacquesidae | Coenobita clypeatus |
The oldest fossil attributed to Anomura is Platykotta, from the Norian–Rhaetian Period in the United Arab Emirates.