A new species of Alvinocaris (Crustacea: Decapoda: Caridea: Alvinocarididae) from hydrothermal vents in the Izu-Bonin and Mariana Arcs, north-western Pacific

A new species of the caridean genus Alvinocaris , A. marimonte sp. nov., is described and illustrated on the basis of specimens collected from hydrothermal vents at three locations in Izu-Bonin and Mariana Arcs of the north-western Pacific Ocean, Myojin Knoll (1224 m depth), NW Eifuku (1574–1582 m depth) and NW Rota seamounts (525 m depth). It is the 17th species assigned to Alvinocaris , and differs from all other congeneric species in several morphological characteristics derived from the rostrum length and armature, the carapace armature, the shape of the posterior margin of the telson and the armature of the third and fourth pereopods. Results of molecular phylogenetic analyses based on partial sequences of the mitochondrial COI and nuclear ITS-I genes compared between specimens of A. marimonte sp. nov. and other known species of Alvinocaris supported our recognition of the new species, although available data are still limited. Alvinocaris marimonte sp. nov. is represented by two morphotypes, distinguished by the armature of the posterior margin of the telson (spines vs plumose setae), which were not detected as separate species by the molecular analysis. Our discovery of the intraspecific variation in the armature of the posterior margin of the telson led us to reassess diagnostic characters used to distinguish species within the genus Alvinocaris .