Anomura

Anomura Temporal range: Norian–Recent PreЄ Є O S D C P T J K Pg N
File:Dardanus megistos2.jpg
The hermit crab Dardanus megistos
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Subphylum:	Crustacea
Class:	Malacostraca
Order:	Decapoda
Suborder:	Pleocyemata
Infraorder:	Anomura Macleay, 1838
Superfamilies
Aegloidea Chirostyloidea † Eocarcinoidea Galatheoidea Hippoidea Lithodoidea Lomisoidea Paguroidea

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).

Description

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 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 (Lithodidae), porcelain crabs (Porcellanidae) and hairy stone crab (Lomisidae) are all separate instances of carcinisation.

As decapods (meaning ten-legged), anomurans have ten pereiopods, but the last pair of these is reduced in size, and often hidden inside the gill chamber (under the carapace) to be used for cleaning the gills. Since this arrangement is very rare in true crabs (for example, the small family Hexapodidae), a "crab" with only eight visible pereiopods is generally an anomuran.

There is wide acceptance from morphological and molecular data that Anomura and Brachyura (true crabs) are sister taxa, together making up the clade Meiura.

Classification

The infraorder Anomura is divided into nine superfamilies:

Superfamily	Members	Families	Photo
Aegloidea	Aegla	Aeglidae
Chirostyloidea	squat lobsters	Chirostylidae Eumunididae Kiwaidae	Eumunida picta
† Eocarcinoidea	† Eocarcinus † Platykotta	† Eocarcinidae † Platykottidae
Galatheoidea	squat lobsters porcelain crabs	Galatheidae Munididae Munidopsidae Porcellanidae † Retrorsichelidae	200px Munidopsis serricornis (Munidopsidae)
Hippoidea	mole crabs or sand crabs	Albuneidae Blepharipodidae Hippidae	200px Blepharipoda occidentalis (Blepharipodidae)
Lithodoidea	king crabs	Hapalogastridae Lithodidae	200px Lithodes santolla (Lithodidae)
Lomisoidea	hairy stone crab	Lomisidae
Paguroidea	hermit crabs coconut crab	Coenobitidae Diogenidae Paguridae Parapaguridae Parapylochelidae Pylochelidae Pylojacquesidae	Coenobita clypeatus (Coenobitidae)

The oldest fossil attributed to Anomura is Platykotta, from the Norian–Rhaetian of the United Arab Emirates.

External links

• Media related to at Wikimedia Commons
• Data related to Anomura at Wikispecies