Pseudocrangonyx Akatsuka & Komai 1922

Genus Pseudocrangonyx Akatsuka & Komai, 1922

syn.: Pseudocrangonyx Akatsuka & Komai, 1922, p. 120, figs 1, 2, (orig. descrip.)—Tomikawa et al. 2008, p. 276 (type species redescrip.)

Type species. Pseudocrangonyx shikokunis Akatsuka & Komai, 1922 [type loc.—water well in Tomioka, Tokushima Prefecture, Shikoku Isl., Japan]

Remarks. Although phenotypic features clearly differentiated a new species from other representatives of the genus Pseudocrangonyx, we compared mt- cox1 sequences from 7 members of the genus to confirm their distinctness. The newly described species well as P. f e b r a s, P. kseniae, and P. korkishkoorum that are also known from Primory and P. susunaensis from neighboring Sakhalin were analyzed.

Each amphipod specimen sequenced for this study was characterized by a unique cox1 sequence (Fig. 2). Five highly similar (pairwise distances 0.025–0.003) P. korkishkoorum accessions KF153105 – KF153109 formed moderately supported (75 %) clade further split into two subclades corresponding to closely located rivers Narva and Barabashevka. This lineage had P. tiunovi, sp. nov. as a sister (100 %). P. susunaensis and P. sympatricus, sp. nov. formed another moderately supported sister pair (79 %) with P. febras branching basally (68 %). Relationship between P. kseniae and P. holsingeri, sp. nov. remained unresolved in our analysis.

There was notable difference in pairwise distances between the sequences. The most distinct from each other were P. susunaensis and P. holsingeri, sp. nov. (0.201) while in most other cases the distances did not exceed 0.150–0.170. Only difference between P. korkishkoorum and P. tiunovi, sp. nov. did not exceed 0.076 although these species clearly differ morphologically (see below).