Thoracotremata

Thoracotremata
Leptograpsus variegatus, Grapsidae
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Malacostraca
Order:	Decapoda
Suborder:	Pleocyemata
Infraorder:	Brachyura
Section:	Eubrachyura
Subsection:	Thoracotremata Guinot, 1977
Families
See text

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]

Brachyura	Dromiacea Raninoida Cyclodorippoida Eubrachyura Heterotremata Thoracotremata

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]

Thoracotremata	Pinnotheridae Dotillidae Percnidae Xenograpsidae Cryptochiridae Ocypodidae Glyptograpsidae Grapsidae Plagusiidae Gecarcinidae Sesarmidae Mictyridae Varunidae Macrophthalmidae

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]

References

1. Sammy De Grave; N. Dean Pentcheff; Shane T. Ahyong; et al. (2009). "A classification of living and fossil genera of decapod crustaceans" (PDF). Raffles Bulletin of Zoology. Suppl. 21: 1–109.
2. 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 (2014). "Evolutionary History of True Crabs (Crustacea: Decapoda: Brachyura) and the Origin of Freshwater Crabs". Molecular Biology and Evolution. 31 (5). Oxford University Press : 1173–1187. doi:10.1093/molbev/msu068.
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. (24 April 2019). "A phylogenomic framework, evolutionary timeline and genomic resources for comparative studies of decapod crustaceans". Proceedings of the Royal Society B. 286 (1901). doi:10.1098/rspb.2019.0079. PMC 6501934. PMID 31014217.