Redescription of Diaphanosoma dubium Manuilova, 1964 (Branchiopoda: Ctenopoda: Sididae), and description of a new, related species

The poorly known D. dubium Manuilova is redescribed on extensive material from more than 80 populations from the Russian Far East, Central Asia, Mongolia, China, Japan, Vietnam, the Philippines, Thailand, Malaysia, Bangladesh, India and Sri Lanka. Its morphological variability and geographical distribution are analysed and supplemented by notes on biology. The conspecificity of morphologically different distant populations is discussed. In the northern part of its range, D. dubium was long confused with D. brachyurum or D. leuchtenbergianum, and in the south with D. modigliani. It seems that the recent appearance of D. dubium in fish ponds of Uzbekistan and Kazakhstan was an introduction, together with Far Eastern fish. D. pseudodubium sp.nov., close to but markedly different, is described from two lakes in the lower Amur river system. D. dubium, D. pseudodubium, D. tropicum and D. modigliani s. str. form a group of related species, widely distributed in Eastern and Southern Asia.