Heterotremata Explained

Heterotremata is a clade of crabs, comprising those crabs in which the genital openings are on the sternum in females, but on the legs in males. It comprises 68 families in 28 superfamilies.^[1]

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:^{[2] [3]}

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:^[2]

Superfamilies

• Aethroidea
• Bellioidea
• Bythograeoidea
• Calappoidea
• Cancroidea
• Carpilioidea
• Cheiragonoidea
• Corystoidea
• Dairoidea
• Dorippoidea
• Eriphioidea
• Gecarcinucoidea
• Goneplacoidea
• Hexapodoidea
• Leucosioidea
• Majoidea
• Orithyioidea
• Palicoidea
• Parthenopoidea
• Pilumnoidea
• Portunoidea
• Potamoidea
• Pseudothelphusoidea
• Pseudozioidea
• Retroplumoidea
• Trapezioidea
• Trichodactyloidea
• Xanthoidea

However, recent studies have found the following superfamilies and families to not be monophyletic, but rather paraphyletic or polyphyletic:^{[2] [3]}

• 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

Notes and References

1. . 2009 . Suppl. 21 . 1–109 . A classification of living and fossil genera of decapod crustaceans . Sammy De Grave . N. Dean Pentcheff . Shane T. Ahyong . etal . dead . https://web.archive.org/web/20110606064728/http://rmbr.nus.edu.sg/rbz/biblio/s21/s21rbz1-109.pdf . 2011-06-06 .
2. Evolutionary History of True Crabs (Crustacea: Decapoda: Brachyura) and the Origin of Freshwater Crabs . Ling Ming Tsang . Christoph D. Schubart . Shane T. Ahyong . Joelle C.Y. Lai . Eugene Y.C. Au . Tin-Yam Chan . Peter K.L. Ng . Ka Hou Chu . . Oxford University Press . 31 . 5 . 2014 . 1173–1187 . 10.1093/molbev/msu068 . free.
3. Wolfe . Joanna M. . Breinholt . Jesse W. . Crandall . Keith A. . Lemmon . Alan R. . Lemmon . Emily Moriarty . Timm . Laura E. . Siddall . Mark E. . Bracken-Grissom . Heather D. . A phylogenomic framework, evolutionary timeline and genomic resources for comparative studies of decapod crustaceans . Proceedings of the Royal Society B . 24 April 2019 . 286 . 1901 . 10.1098/rspb.2019.0079 . 6501934 . 31014217 . free .