Taxonomic revision of Microcotyle caudata Goto, 1894 parasitic on gills of sebastids (Scorpaeniformes: Sebastidae), with a description of Microcotyle kasago n. sp. (Monogenea: Microcotylidae) from off Japan.

Two species of microcotylid monogeneans, Microcotyle caudata Goto, 1894 and Microcotyle sebastisci Yamaguti, 1958, have been reported from fishes of the Sebastes inermis species complex and Sebastiscus marmoratus (Cuvier) (Scorpaeniformes: Sebastidae). So far, these parasite species have been distinguished by the size of the eggs and the number of testes, but based on morphological evidence including re-examination of the type-specimens and topotypes and molecular analysis, we consider M. sebastisci to be a junior synonym of M. caudata. As a result, M. caudata exhibits a wide host range, seven species from three genera and two families. A new species, Microcotyle kasago n. sp., is described based on material from S. marmoratus and differentiated from other congeners by means of morphological and molecular analysis.