Parasesarma semperi (Bürger, 1893) was first described from Bohol in the Philippines and is considered to be widely distributed in Southeast Asia. Parasesarma longicristatum (Campbell, 1967) was originally described as a subspecies of P. semperi from Queensland, Australia, and later recognised as a full species. In this study, we re-examine specimens of the two species from across their entire geographic range using genetic markers, a morphometric analysis, and traditional morphological characters. Previous taxonomic species diagnoses were found to be unreliable, but morphometric principle component analyses consistently separate the two species, with the length to width ratio of the propodus of the fourth pereiopod being of particular importance. Genetic data corresponding to the mitochondrial genes COI, ND1 and 16S confirmed a close sister relationship between the two species, forming reciprocally monophyletic groups. Both species have high haplotype diversities and high intraspecific gene flow.