We describe three free-living marine nematode species from Sagami Bay, Japan. Wiesoncholaimus jambiosp. nov. is the second species of this genus. It differs from the type species, Wiesoncholaimus mawsonae Inglis, 1966, by its dorsal tooth, which is as long as the other two teeth; its conico-cylindrical tail, which is as long as 4.6-4.8 cloacal body diameters; and the absence of the gubernaculum. Thalassironus cf. britannicus de Man, 1889 agrees well with a redescription of Thalassironus britannicus de Man, 1889 based on specimens collected near the type locality. However, as it is possible that T. britannicus sensu lato includes two or more species, our species may not be conspecific to T. britannicus sensu stricto. Vasostoma cf. longispicula Huang and Wu, 2010 closely resembles Vasostoma longispicula Huang and Wu, 2010 originally described from China, but minor differentiations are observed in body diameter, body cuticle thickness, and type of precloacal supplements.
Keywords: JAMBIO; North Pacific; invertebrates; meiofauna; new species.