A revision of "blanket-hermit crabs" of the genus Paguropsis Henderson, 1888, with the description of a new genus and five new species (Crustacea, Anomura, Diogenidae).

For 130 years the diogenid genus Paguropsis Henderson, 1888 was considered monotypic for an unusual species, P. typica Henderson, 1888, described from the Philippines and seldom reported since. Although scantly studied, this species is known to live in striking symbiosis with a colonial sea anemone that the hermit can stretch back and forth like a blanket over its cephalic shield and part of cephalothoracic appendages, and thus the common name "blanket-crab". During a study of paguroid collections obtained during recent French-sponsored biodiversity campaigns in the Indo-West Pacific, numerous specimens assignable to Paguropsis were encountered. Analysis and comparison with types and other historical specimens deposited in various museums revealed the existence of five undescribed species. Discovery of these new species, together with the observation of anatomical characters previously undocumented or poorly described, including coloration, required a revision of the genus Paguropsis. The name Chlaenopagurus andersoni Alcock & McArdle, 1901, considered by Alcock (1905) a junior synonym of P. typica, proved to be a valid species and is resurrected as P. andersoni (Alcock, 1899). In two of the new species, the shape of the gills, length/width of exopod of maxilliped 3, width and shape of sternite XI (of pereopods 3), and armature of the dactyls and fixed fingers of the chelate pereopods 4, were found to be characters so markedly different from P. typica and other species discovered that a new genus for them, Paguropsinagen. n., is justified. As result, the genus Paguropsis is found to contain five species: P. typica, P. andersoni, P. confusasp. n., P. gigassp. n., and P. laciniasp. n. Herein, Paguropsinagen. n., is proposed and diagnosed for two new species, P. pistillatagen. et sp. n., and P. inermisgen. et sp. n.; Paguropsis is redefined, P. typica and its previously believed junior synonym, P. andersoni, are redescribed. All species are illustrated, and color photographs provided. Also included are a summary of the biogeography of the two genera and all species; remarks on the significance of the unusual morphology; and remarks on knowledge of the symbiotic anemones used by the species. To complement the morphological descriptions and assist in future population and phylogenetic investigations, molecular data for mitochondrial COI barcode region and partial sequences of 12S and 16S rRNA are reported. A preliminary phylogenetic analysis using molecular data distinctly shows support for the separation of the species into two clades, one with all five species of Paguropsis, and another with the two species Paguropsinagen. n.