Neoheterobothrium hirame sp. nov.is described, based on specimens collected from the buccal cavity wall of Japanese flounder, Paralichthys olivaceus, caught in Wakasa Bay, Japan. The parasite was 14-33 mm in total length, with 4 pairs of clamps on the pedunculated haptor, which was separated from the body proper by a long isthmus. The presence of a pair of peripheral intestinal branches running along both sides of body, in addition to the main pair of medial branches, is described here for the first time.The new species can be distinguished from N. affine (Linton, 1898) --the most closely related species and the type species of the genus--by the relatively large body proper and the shorter isthmus. The taxonomic status of other related species is discussed. The generic diagnosis proposed by Price (1943), Yamaguti (1963) and Mamaev (1987) is emended.