Endemism of subterranean Diacyclops in Korea and Japan, with descriptions of seven new species of the languidoides-group and redescriptions of D. brevifurcus Ishida, 2006 and D. suoensis Ito, 1954 (Crustacea, Copepoda, Cyclopoida)

This work explores for the first time comprehensively the diversity and endemism of subterranean copepod crustaceans from the genus Diacyclops in the Far East. Previous scarce records have indicated presence of only a few widely distributed species, despite relative isolation of subterranean habitats in this part of the world and very dynamic changes in topography during the Pleistocene glacial cycles. A wide range of samples from Korea and Japan are studied, and all previous records of subterranean Diacyclops are re-evaluated. Morphological analyses of microcharacters, many of which are used in cyclopoid taxonomy for the first time herein, reveal high diversity in both countries. No subterranean species is found in common, although the existence of four sibling species pairs is probably indicative of relatively recent speciation. Seven species are described as new to science and two are re-described. This research provides evidence for the importance of subterranean habitats as reservoirs of biodiversity, and also demonstrates the inadequacy of current morphological methods for identifying closely related species of copepods. The disproportionately high diversity and short-range endemism discovered around Lake Biwa provides further evidence for the role of ancient lakes as biodiversity pumps for subterranean habitats.