Although most members of the freshwater leech family Glossiphoniidae have mid-body somites divided into three annuli, the genus Torix Blanchard, 1893 is distinguished by two-annuli somites. Torix has high species richness in Far East Asia, and three nominal species have been recognised in the Japanese Archipelago and adjacent regions that can be distinguished by a combination of both internal and external morphological characteristics. However, recent studies have shown that these diagnostic features are ontogenetically variable and this has resulted in taxonomic confusion among Torix species endemic to the Japanese Archipelago. In this study, we revisit the taxonomic accounts of T. orientalis (Oka, 1925) and T. tagoi (Oka, 1925), in addition to that of the recently redescribed T. tukubana (Oka, 1935) to clarify the diagnostic characteristics for each of the three species. Our morphological and molecular phylogenetic analyses demonstrated that the three Torix species in Japan are indistinguishable. We therefore conclude that these species should be synonymised and treated as a single species. The specific names orientalis and tagoi were simultaneously established under the genus Oligobdella Moore, 1918, therefore we acted as First Reviser and gave precedence to the name O. tagoi, thus the valid name for the Far East Asian Torix species is T. tagoi unless T. orientalis and T. tagoi are treated as distinct species. There are several type localities for T. tagoi and the name-bearing types have been lost, therefore we designate a neotype for this species to obviate zoological and nomenclatural issues.

ZooBank: urn:lsid:zoobank.org:pub:E2DBF999-3B51-456F-AB04-A7D138E0AF2D