Proposal to synonymize Neoplagioporus Shimazu, 1990 with Urorchis Ozaki, 1927; taxonomic revision and the description of Urorchis takahaya n. sp.

Urorchis Ozaki, 1927 and Neoplagioporus Shimazu, 1990 (Digenea: Opecoelidae: Sphaerostomatinae) comprise species parasitic in freshwater fishes of eastern Asia, although the status of these genera is questionable. We revised these genera, primarily using evidence from a molecular phylogeny based on nuclear ribosomal DNA, including new sequences of four known and one new species. Urorchis was part of the clade of Neoplagioporus species, rendering the genus Neoplagioporus paraphyletic. Based on this evidence, we regard Neoplagioporus as a junior synonym of Urorchis, and amend its taxonomic diagnosis. Moreover, we consider Neoplagioporus kajika Urabe & Higa, 2006 to be a junior synonym of Urorchis zacconis (Yamaguti, 1934). Finally, we describe a new species, Urorchis takahaya n. sp., from upstream fat minnow Rhynchocypris oxycephalus collected in an inlet of Lake Biwa, Shiga, Japan.