Cycloxanthops angustus Rathbun, 1906, C. cavatus Rathbun, 1907, and Medaeus noelensis Ward, 1934, are three Indo-West Pacific small cryptic species of xanthid crabs with extensive distributions ranging from the western Indian Ocean to Hawaii and Polynesia. Their generic status has long been uncertain. Cycloxanthops angustus has several distinctive characters that exclude this species from Cycloxanthops or Neoxanthops as currently defined, including the relatively quadrate and flattened carapace; form of the carapace areolation; structure of the anterolateral teeth and a serrulate merus on ambulatory legs. Cycloxanthops cavatus has many basic differences in morphology such as the anterolateral margin of the carapace, its frontal margin and the distinctly sculptured dorsal surface; the fingers of the chelipeds short and not pigmented black, and the distal structure of first pleopod. Medaeus noelensis too possesses diagnostic features: the narrow and rectangular basal antennular segment that fits tightly into the orbital hiatus, the short carapace frontal margin that folds downwards and inwards and a special peeling tooth on the right chela for opening gastropods. This present study reappraises the taxonomic position of these three enigmatic species and shows that they are not related to the genera they are currently assigned. Consequently, three new monotypic genera are established Marratha n. gen., with M. angusta n. comb.; Jacforus n. gen., with J. cavatus n. comb.; and Danielea n. gen., with D. noelensis n. comb., and their relationship with each other as well as affiliated taxa are discussed.
Crustacea, Decapoda, Brachyura, Xanthoidea, Xanthidae, Indo-West Pacific, new genera, new combinations.