New species of Tortanus (Copepoda; Calanoida) from stomach contents of chum salmon juveniles collected from the Sea of Japan

Tortanus (Eutortanus) komachi n. sp. {Copepoda: Calanoida) is described from specimens found in the stomach contents of juvenile chum salmon captured off the northern Japanese coast of the Sea of Japan. The new species, known only from the type locality, is most closely related to T. (E.) derjugini, a species that is widely distributed from the Sea of Okhotsk to the South China Sea, with an isolated population in the Ariake Sea, southwestern Japan. The evolutionary process leading to the new species is discussed on the basis of the zoogeography of the subgenus.