A new spinicaudatan (Crustacea : Branchiopoda) from the Island of Olkhon (Lake Baikal, Russia) and the zoogeography of East Asian spinicaudata

Abstract

A spinicaudatan branchiopod crustacean, Baikalolkhonia tatianae gen. et sp. nov., is described from the Baikal region in Russia. The genus is assigned to the family Cyzicidae Stebbing, 1910, based on the absence of a frontal organ on the head, the absence of triangular epipodal laminae on the thoracopods, and the presence of a pair of large frontal spines on the telson. The main distinguishing characteristic is that the epipodal upper corners of many anterior thoracopods (including even the first pair) are transformed into "sausage-like organs." Since such epipodal processes have been until now unknown in the Cyzicidae, the diagnosis of the family is emended, and 2 newly defined subfamilies, Baikalolkhoniinae and Cyzicinae, are proposed. Up to the present, 11 species belonging to 7 genera in 4 families of Spinicaudata (Cyclestheriidae, Cyzicidae, Leptestheriidae, and Limnadiidae) are known from the neighboring regions of East Asia, including the Russian Far East, Mongolia, China, Korea, and Japan. The list of species and the key to the species are provided. Their distribution defines 4 zoogeographical provinces, and the species diversity clearly shows a latitudinal gradient in a similar pattern to the European fauna.