Tortanus derjugini Smirnov (Copepoda: Calanoida) from the Ariake Sea, western Japan, with notes on the zoogeography of brackish-water calanoid copepods in East Asia
Tortanus (Eutortanus) derjugini
Tortanus (Eutortanus) derjugini Smirnov is redescribed from brackish regions of the Ariake Sea, western Japan. The copepod is presumed to be an Asian continental relict because of its exclusive occurrence in Asian continental waters and the Ariake Sea in Japan. A comparison between specimens from Japanese, Korean and Chinese waters is made, and some differences were detected in the anal somite and caudal rami of females between Japanese and Korean specimens; the length/width ratio of the anal somite and the ratio of the right caudal ramus to the left one are significantly lower in the former. These differences indicate that the isolation of the Ariake Sea population from the Asian continental populations since the last transgression (ca. 6,000-10,000 years ago) has caused no great morphological variation. Zoogeography of brackish-water calanoid copepods including this species in East Asia is discussed. There are three types of distribution patterns that are supposed to be related to geological events occurring during the Cenozoic era.
Copyright (c) 1995 The Plankton Society of Japan