Description of Metopograpsus cannicci, new species, a pseudocryptic crab species from east Africa and the Western Indian ocean (Decapoda: Brachyura: Grapsidae)

The Indo-Pacific genus Metopograpsus H. Milne Edwards, 1853, of the family Grapsidae (Decapoda: Brachyura: Thoracotremata) comprises six recognised species of intertidal crabs from sheltered rocky shores and mangrove forests. Recent molecular evidences suggest that Metopograpsus thukuhar (Owen, 1839) and M. quadridentatus Stimpson, 1858, could represent species complexes, each consisting of two species. Here we deal with M. thukuhar and its genetic separation into two clusters, one with all East African specimens, including samples from the Red Sea, Iran, and the Seychelles, and the other one comprising all the known specimens from Southeast Asia and Pacific islands. In this paper, we present new results of an in-depth morphological investigation of samples assigned to M. thukuhar, designate a neotype, and confirm the presence of an undescribed species by adding support from nuclear DNA comparisons. With respect to M. thukuhar, which was originally described from Hawaii, the new species corresponds to samples from the western Indian Ocean. The distinguishing morphological characters include differences in the shape of the first male gonopod. While the observed differences are relatively subtle, they nevertheless support the differentiation revealed by molecular findings. Therefore, we refer to the new species as a pseudocryptic taxon and name it Metopograpsus cannicci. The description of this new taxon elevates the species number within Metopograpsus to seven and adds another record to the list of newly described crabs from the Western Indian Ocean mangroves.