Thoracotremata Explained

Thoracotremata is a clade of crabs, comprising those crabs in which the genital openings in both sexes are on the sternum, rather than on the legs. It comprises 17 families in four superfamilies .^[1]

Evolution

Thoracotremata is the sister group to Heterotremata 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 Thoracotremata 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 and families

• Ocypodoidea
  • Camptandriidae
  • Dotillidae
  • Heloeciidae
  • Macrophthalmidae
  • Mictyridae
  • Ocypodidae
  • Ucididae
  • Xenophthalmidae
• Pinnotheroidea
  • Pinnotheridae

• Cryptochiroidea
  • Cryptochiridae
• Grapsoidea
  • Gecarcinidae
  • Glyptograpsidae
  • Grapsidae
  • Plagusiidae
  • Sesarmidae
  • Varunidae
  • Xenograpsidae

However, recent studies have found the superfamilies Grapsoidea and Ocypodoidea to be polyphyletic and invalid.^{[2] [3]}

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.
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 .