A New Species of the Genus Rhyacodrilus Bretscher (Oligochaeta, Tubificidae) from Japanese Lakes

A new tubificid oligochaete, Rhyacodrilus hiemalis sp. nov., is described from four lakes in central Japan. This species resembles R. coccineus (Vejdovsky), R. sodalis (Eisen) and their unclear relatives (the Far East Russian R. sokolskajae Semernoi and R. sibiricus Semernoi, the Chinese R. sinicus (Chen)), but is distinguished from these congeners by having many long hair chaetae, many long intermediate teeth on the dorsal pectinate chaetae, ventral pectinate chaetae, and masses of gland cells around the male pores. This species is an annual that breeds during the cold season but aestivates in deeper sediment in summer.