A revision of Carcinoplax abyssicola (Miers, 1885) and seven related species of Carcinoplax H. Milne Edwards, 1852, with the description of two new species and an updated key to the genus (Crustacea, Decapoda, Brachyura, Goneplacidae)

The identities of the deep-water brachyuran crabs Carcinoplax abyssicola (Miers, 1885), C. longipes (Wood-Mason, 1891), and C. specularis Rathbun, 1914 (family Goneplacidae MacLeay, 1838) are clarified on the basis of the examination of types and of an extensive series of specimens from the Indo-West Pacific region, including colour photographs of fresh specimens. Two species described from the Philippines, C. verdensis Rathbun, 1914 and C. polita Guinot, 1989, and previously synonymised under C. specularis, are shown to be distinct species. Two new species, C. adelphia n. sp. and C. jugum n. sp., are described from Vanuatu and the Philippines, respectively. Carcinoplax adelphia n. sp. differs from the closely allied C. specularis by having a male first gonopod (G1) that is relatively more elongated, particularly the distinctly more slender distal half, than the G1 of C. specularis. Carcinoplax jugum n. sp. is characterized by a suite of characters that includes an epistome with strongly concave lateral margins, a carapace having distinctly swollen gastric and cardiac regions, and a G1 with a subconical distal part. The taxonomies of these seven species, as well as that of the allied C. fasciata Ng & Kumar, 2016 from southwestern India, are revised. A revised, updated key to the 25 known species of Carcinoplax H. Milne Edwards, 1852 is also provided.