Sympatric colour morphs or distinct taxa? Examining species boundaries among two South African freshwater crabs (Decapoda: Potamonautidae: Potamonautes MacLeay, 1838), with the description of a new species

A new pearl white freshwater crab was collected in sympatry with Potamonautes sidneyi (Rathbun, 1904) in the Indian Ocean coastal belt forest at Mbotyi on the Wild Coast of the Eastern Cape Province, South Africa. Specimens of the two sympatric congeneric species were subjected to DNA sequencing of three partial mitochondrial loci (COI, 12S rRNA and 16S rRNA) together with morphological examination. Phylogenetic analyses of the new species were undertaken to determine its evolutionary relationship with the other east and southern African species of freshwater crabs. Results revealed that, Potamonautes mhlophe sp. nov. is sister to P. dentatus (Stewart & Cook, 1995) and distantly related to the sympatric P. sidneyi. The two congeneric sympatric species were characterised by the absence of shared COI haplotypes and marked sequence divergence value for the latter locus. Furthermore, Potamonautes mhlophe sp. nov. is morphologically distinct from P. sidneyi based on the structure of the first and second gonopods. Considering the congruence between the mtDNA and morphology, the new species is herein described.