Molecular phylogeny of grapsoid crabs from East Africa based on two mitochondrial genes and a proposal for refraining from current superfamily classification

Grapsoid and ocypodoid crabs receive a lot of attention in the literature due to their predominance and important role as primary and secondary consumers in intertidal as well as supratidal marine habitats. They are especially species-rich in the tropics, where they have been found to repeatedly invade terrestrial and freshwater habitats. However, the systematics of the crabs belonging to these two superfamilies is still not settled, despite recent steps clarifying phylogenetic relationships and introducing new taxa. In this study, a molecular phylogeny of grapsoid crabs primarily based on East African representatives is constructed based on DNA sequences of the mitochondrial small and large ribosomal subunits (12S and 16S rRNA), thus complementing previous molecular taxonomic studies that had been carried out with the American and East Asian fauna. In addition, selected representatives of all ocypodoid families and subfamilies were included. The monophyly of Grapsidae, Ocypodidae (sensu stuctu), Sesarmidae and Varunidae is well confirmed, if the genera Cyclograpsus, Helice are considered Varunidae and Euchirograpsus a Plagusiidae, as previously suggested. The monophyly of the family Gecarcinidae cannot be supported with our data. The family Plagusiidae in its present composition is polyphyletic. Special attention was given to the large family Sesarmidae, which has many endemic genera in the Indo-West Pacific. According to this study, two of the most speciose genera, Chiromantes and Parasesarma, are not monophyletic and need to be redefined. On the higher taxonomic level, it becomes evident that both superfamilies, Grapsoidea and Ocypodoidea, are not monophyletic in their current composition, as exemplified by a proposed sister group relationship of Varunidae and Macrophthalmidae. These results confirm those from previous molecular studies and we therefore propose to refrain from the traditional use of the Grapsoidea and Ocypodoidea as monophyletic superfamilies and treat the constituent families separately.