East Asian Cymonomid Crabs (Crustacea: Brachyura)

Shane T. Ahyong and Peter K.L. Ng (2017) Cymonomid crabs are small cryptic deep-water brachyurans occurring worldwide. Six species have been reported from East Asia: one from both Taiwan and Japan (C. andamanicus Alcock, 1905) and five from Japan only (C. curvirostris Sakai, 1965, C. japonicus Balss, 1922, C. sagamiensis Sakai, 1983, C. soela Ahyong and Brown, 2003, C. umitakae Takeda, 1981). Cymonomus curvirostris, C. japonicus, C. sagamiensis and C. umitakae were described from Japanese waters, but C. andamanicus and C. soela have much more distant type localities - the Andaman Sea and southeastern Australia, respectively. We review all previous records of Cymonomus from East Asia, describe two new species, and clarify the status of records of C. andamanicus and C. soela from the region. Records of C. andamanicus and C. soela from East Asia are referable to two new species occurring in both Taiwan and Japan. The identities of C. japonicus and C. sagamiensis are fixed by neotype selection; C. sagamiensis is made a junior objective synonym of C. umitakae. Six species of Cymonomus are now recorded from Japan, of which two also occur off Taiwan. We also report on cymonomids collected by Taiwanese research vessels in the South China Sea (Dongsha and Macclesfield Bank) of which four species were collected, including C. hakuhoae Takeda and Moosa, 1990, not previously found in Japan or Taiwan. A key to the species of Cymonomus from East Asia and the South China Sea is included.