Molecular phylogeny of the crab genus Brachynotus (Brachyura : Varunidae) based on the 16S rRNA gene

The crab genus Brachynotus de Haan, 1833 is restricted to the intertidal an d shallow subtidal of the Mediterranean and northeastern Atlantic. It is pr esently recognized to consist of four species, of which three (B. foresti, B. gemmellari and B. sexdentatus) are endemic to the Mediterranean. The fou rth species, B. atlanticus, is found along the Atlantic coasts of northern Africa and southern Europe, but also extends into the western Mediterranean . This high level of endemism suggests that speciation within Brachynotus i s strongly correlated with the geography and geology of the Mediterranean S ea. A molecular phylogeny based on the mitochondrial large subunit (16S) rR NA gene indicates that the four species of Brachynotus form a monophyletic group within Atlantic Varunidae. The DNA sequence data also show that the g enus Brachynotus can be subdivided into two species groups, one comprising B. atlanticus and B. foresti, and the other one B. gemmellari and B. sexden tatus. While B. atlanticus and B. foresti are clearly genetically distinct, B. gemmellari and B. sexdentatus are identical in the studied region of th e 16S rRNA gene, suggesting a recent separation or continuing gene flow.