The hydrothermal vent crab Xenograpsus testudinatus NK Ng, Huang & Ho, 2000 (Xenograpsidae), originally described from Kueishan in northern Taiwan, has the been the subject of many ecological and physiological studies in the island and Japan. The species is morphologically similar to the Japanese X. novaeinsularis Takeda & Kurata, 1977, reported from Ogasawara Islands, being supposedly separated by characters of the carapace, proportions and form of the third maxillipeds, chelae, ambulatory legs male pleon and male first gonopod. Earlier studies have shown that most of these differences are not taxonomically reliable and only some carapace characters are able to distinguish them. Genetic analyses of the mitochondrial COI and 16S rRNA genes from specimens of both species across the distribution, including material from or adjacent to their type localities, confirm that previous diagnostic interspecific characters are intraspecific variations, and even the carapace differences do not work. Xenograpsus testudinatus is here regarded as a junior synonym to X. novaeinsularis. Xenograpsus currently contains two species, with X. novaeinsularis in the West Pacific and X. ngtama McLay, 2007, from New Zealand, with the two species being morphologically and genetically distinct.
Integrated taxonomy, Distribution, Type material, Synonymy, Hydrothermal vent crab
