Heterotremata

 ( Crabs ) 

Heterotremata is a clade of , comprising those crabs in which the genital openings are on the sternum in females, but on the arthropod leg in males. It comprises 68 families in 28 superfamilies.

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Evolution Heterotremata is the sister group to Thoracotremata within the clade Eubrachyura, having diverged during the Cretaceous period. Eubrachyura itself is a subset of the larger clade Brachyura, which consists of all "true crabs". A summary of the high-level internal relationships within Brachyura can be shown in the cladogram below:

The internal relationships within Heterotremata are less certain, with many of the superfamilies found to be invalid. The proposed cladogram below is from analysis by Tsang et al, 2014:

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Superfamilies

• Aethridae
• Belliidae
• Bythograeidae
• Calappoidea
• Cancroidea
• Carpilioidea
• Cheiragonoidea
• Corystidae
• Dairoidea
• Dorippoidea
• Eriphioidea
• Gecarcinucoidea
• Goneplacoidea
• Hexapodidae
• Leucosioidea
• Majoidea
• Orithyioidea
• Palicoidea
• Parthenopidae
• Pilumnoidea
• Portunoidea
• Potamoidea
• Pseudothelphusoidea
• Pseudozioidea
• Retroplumidae
• Trapezioidea
• Trichodactyloidea
• Xanthoidea

However, recent studies have found the following superfamilies and families to not be monophyletic, but rather paraphyletic or polyphyletic:

• The superfamilies Calappoidea, Eriphioidea, and Goneplacoidea are polyphyletic
• The superfamily Potamoidea is paraphyletic with respect to Gecarcinucoidea, which is resolved by placing Gecarcinucidae within Potamoidea
• The Majoidea families Epialtidae, Mithracidae and Majidae are polyphyletic with respect to each other
• The Xanthoidea family Xanthidae is paraphyletic with respect to Panopeidae

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