A new species of Orobdella (Hirudinida, Arhynchobdellida, Gastrostomobdellidae) and redescription of Orobdella kawakatsuorum from Hokkaido, Japan with the phylogenetic position of the new species.

A new quadrannulate Orobdella Oka, 1895 species, Orobdella koikeisp. n., is described on the basis of six specimens collected from Hokkaido, Japan. In addition, an emended description of quadrannulate Orobdella kawakatsuorum Richardson, 1975 is also provided. Orobdella koikei differs from other quadrannulate species of Orobdella in possessing the following combination of characters: color dorsally brown, IV uniannulate, male gonopore at XI b6, gastropore and female gonopore at XIII a1, 1/2 + 4 + 1/2 between gonopores, XXV triannulate, tubular but bulbous at junctions with gastropore and crop gastroporal duct, epididymides in XVII to XIX, and atrial cornua ovate. The phylogenetic position of the newly described species is estimated using mitochondrial COI, tRNA(Cys), tRNA(Met), 12S rDNA, tRNA(Val) and 16S rDNA markers. Orobdella koikei is a sister taxon of Orobdella kakawatsuorum according to the molecular phylogenetic analyses.