Anomura

 ( Arthropod Infraorders ) 

Anomura (sometimes Anomala) is a group of decapod , including and others. Although the names of many anomurans include the word crab, all true are in the sister group to the Anomura, the Brachyura (the two groups together form the clade Meiura).

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Description The name Anomura derives from an old classification in which Reptantia 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.

Gary Poore (2025). 9780643099258, CSIRO Publishing. ISBN 9780643099258

The group has been moulded by several instances of carcinisation – the development of a crab-like body form.

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

As decapods (meaning ten-legged), anomurans have ten , 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 Crab (for example, the small family Hexapodidae), a "crab" with only eight visible pereiopods is generally an anomuran.

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Evolution

The infraorder Anomura belongs to the group Reptantia, which consists of the walking/crawling decapods (lobsters and crabs). There is wide acceptance from morphological and molecular data that Anomura and Brachyura ("true" crabs) are sister taxa, together making up the clade Meiura. Anomura likely diverged from Brachyura in the Late Triassic period, with the earliest discovered Anomuran fossil Platykotta akaina dating from the Norian–Rhaetian aged Ghalilah Formation of the United Arab Emirates.

The cladogram below shows Anomura's placement within the larger order Decapoda, from analysis by Wolfe et al. (2019).

Some of the internal relationships within Anomura are shown in the cladogram below, which shows Hippidae as sister taxon to Paguroidea, and resolves Parapaguridae outside of Paguroidea:

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Classification

The infraorder Anomura contained seven extant superfamilies:

Aegla sp.

Eumunida picta

Munidopsis serricornis (Munidopsidae)

Blepharipoda occidentalis (Blepharipodidae)

Lomis hirta (Lomisidae)

Coenobita clypeatus (Coenobitidae)

The oldest fossil attributed to Anomura is Platykotta, from the Norian–Rhaetian (Late Triassic) Period in the United Arab Emirates.

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External links

Categories: Arthropod Infraorders, Norian First Appearances, Extant Late Triassic First Appearances

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