Species distribution ranges of Ilyocryptus Sars, 1862 (Cladocera: Ilyocryptidae) fit the transitional zone between Boreal and Tropical Provinces in the Far East

Abstract

In previous papers, it was shown that the Far East is a territory where moving south, Boreal fauna is fluently changed to Tropical fauna. Kotov (2016) proposed to place all taxa from the northern portion of Far East in several faunistic complexes according to the area of their differentiation in the past, i.e. in Pleistocene refugia. But many daphniids and chydorids were placed in an artificial group of non-revised taxa rather than a certain faunistic complex. Ilyocryptids are less numerous and better studied, and they could be used as a model group to test such an approach. Totally, 10 species were found in the Far East: from the very common I. spinifer group, the relatively common I. acutifrons, I agilis, I. yooni, I. raridentatus and I. cuneatus to the very rare I. cf. bhardwaji, I. isanensis, I. thailandensis and I. uenoi. Note that four species are found in Vietnam for the first time, namely, I. isanensis, I. cf. raridentatus, I. thailandensis and I. yooni. In contrast to the aforementioned daphniids and chydorids, ten Far Eastern ilyocryptid taxa accurately fit three faunistic complexes: WE—widely distributed in North Eurasia; ST—southern tropical; EN—Far Eastern endemic. Ilyocryptid distribution fits well with the “wide transitional zone concept” between “Palaearctic” (in reality, we have found that its separation within the Holarctic does not work well for the cladocerans) and Oriental zones, and such our conclusion is made based on the analysis of the adequately known group.