A new opheliid polychaete, Euzonus japonicus sp. nov., is described. This species was collected from subtidal zones in Japanese coasts, while most Euzonus species inhabit intertidal sandy beaches. E. japonicus sp. nov. is morphologically most similar to another subtidal species, E. flabelliferus (Ziegelmeier, 1955) collected from northern Europe, but different from that in the form of branchiae. They share a unique characteristic on setiger 10, i. e., a pair of lateral transverse rows of conical cirri, instead of a pair of lateral smooth ridges that are common to all intertidal Euzonus species.
