Eucyclops roseus, a new Eurasian copepod, and the E. serrulatus-speratus problem in Japan

Abstract

A new Eucyclops species similar to E. serrulatus and E. speratus is described as Eucyclops roseus. The species seems to be distributed widely in Europe and Asia. The confusing taxonomical status of E. serrulatus and E. speratus in Japanese waters has been partly solved by the recognition of this new species. Eucyclops speratus s. str. does not occur in Japan, while E. roseus, E. serrulatus, and the speratus-like species complex are distributed from the Ryukyu Islands to Hokkaido. This species complex may be divided into several taxa ; one is distributed mainly in the northern half of Japan, and the others mainly in the southern half. The habitats of E. roseus and the E. speratus-like species complex in Japan are ponds, lakes, and the middle and lower reaches of rivers and streams, while E. serrulatus is generally restricted to mountain waters and springs.