Anomura (sometimes Anomala) is a group of decapod crustaceans, including hermit crabs and others. Several groups such as the king crabs and porcelain crabs within the Anomura have independently undergone carcinisation, acquiring the armoured crab body plan with a concealed tail. It is the sister group to the "true crabs" or Brachyura.
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. a "crab" with only eight visible pereiopods is generally an anomuran.
Some of the internal relationships within Anomura are shown in the cladogram below, which shows Hippidae as sister to Paguroidea, and resolves Parapaguridae outside of Paguroidea:
{| class="wikitable"
! Superfamily !! Members !! Families !! Photo
|-
| Aegloidea || Aegla || Aeglidae || 200px<br />Aegla sp.
|-
| Chirostyloidea || squat lobsters || Chirostylidae<br />Eumunididae<br />Kiwaidae || 200px<br />Eumunida picta
|-
| † Eocarcinoidea || † Eocarcinus<br />† Platykotta || † Eocarcinidae<br />† Platykottidae ||
|-
| Galatheoidea || squat lobsters<br />porcelain crabs || Galatheidae<br />Munididae<br />Munidopsidae<br />Porcellanidae<br />† Retrorsichelidae || 200px<br />Munidopsis serricornis<br />(Munidopsidae)
|-
| Hippoidea || mole crabs<br />or sand crabs || Albuneidae<br />Blepharipodidae<br />Hippidae || 200px<br />Blepharipoda occidentalis<br />(Blepharipodidae)
|-
| Lomisoidea || hairy stone crab || Lomisidae || 200px<br />Lomis hirta<br />(Lomisidae)
|-
| Paguroidea || hermit crabs<br />coconut crab || Coenobitidae<br />Diogenidae<br />Lithodidae<br />Paguridae<br />Parapaguridae<br />Probeebeidae<br />Pylochelidae<br />Pylojacquesidae<br />Xylopaguridae || 200px<br />Coenobita clypeatus<br />(Coenobitidae)
|}
The oldest fossil attributed to Anomura is Platykotta, from the Norian–Rhaetian (Late Triassic) Period in the United Arab Emirates.