Redescription of Cytherissa pennata Mazepova 1990 and Cytherissa latirecta Mazepova 1985 (Ostracoda, Podocopida, Cytherideidae) from Lake Baikal
摘要
—An illustrated redescription of females and males of two rare species of the genus Cytherissa Sars 1925 (Cytherissa pennata Mazepova 1990 and Cytherissa latirecta Mazepova 1985, both endemic to Lake Baikal, Siberia) is provided. The work was carried out on the basis of syntypes from the type collection of G.F. Mazepova, lectotypes and paralectotypes being designated. The carapace morphology of these species was studied in detail using scanning electron microscopy. The limb structure of both species is described in detail, and the ecology is briefly characterised. Using these two endemic species with different carapace morphology as examples, we have shown that the interspecific differences of Baikalian Cytherissa are not limited to carapace structure. The transformed (geniculate) legs of male C. pennata are located on the right side of the body, vs. on the left side in C. latirecta; and in C. pennata the hinge teeth are on the right valve, vs. on the left valve in C. latirecta. As a result, both these species belong to different lineages of Baikalian Cytherissa. In addition, the limb structure of C. pennata shows fusion of the two distal segments of both legs L5 in both sexes, whereas in C. latirecta the segments are clearly separated. Taking four species (C. pennata, C. latirecta, Cytherissa sp. 1 and Cytherissa sp. 2) as examples, the structural differences in the hemipenes and brush organs of males are considered: they differ in size, the length-to-width ratio, and some other characters. The distal segment of the transformed L6 of males in four different species is shown to have structural features peculiar to each species. These features may well be considered species-specific.