Having been reported in 1898 for the first time from Japanese waters, the lineid heteronemertean Lineus longifissus auct. is known to inhabit tidal flats under the influence of the warm Kuroshio Current along the coasts of Honshu and southwestward, characteristically with a uniformly raisin-colored to black body lacking a caudal cirrus. The taxonomic identity of the Japanese L. longifissus auct. has been questioned by specialists because of some obvious morphological differences between Lineus longifissus (Hubrecht, 1887) s.str. (now in HeteronemertesChernyshev, 1995), originally described from the subantarctic region. In the present study, we describe the Japanese L. longifissus auct. as Corsoua takakurai sp. nov. Before the present study, the genus CorsouaCorrêa, 1963 had been monotypic with the type species Corsoua kristenseniCorrêa, 1963 from the Caribbean. We infer the phylogenetic position of Corsoua takakurai within Lineidae based on the mitochondrial 16S rRNA and cytochrome c oxidase subunit I, and the nuclear 18S rRNA, 28S rRNA, and histone H3 genes.