Redescription of Cytherissa pennata Mazepova 1990 and Cytherissa latirecta Mazepova 1985 (Ostracoda, Podocopida, Cytherideidae) from Lake Baikal

Illustrated redescription of females and males of two rare species of the genus Cytherissa Sars 1925, both endemic to Lake Baikal, Siberia, are provided: Cytherissa pennata Mazepova 1990 and Cytherissa latirecta Mazepova 1985. The work was carried out on the basis of syntypes from the type collection of G. F. Mazepova, lectotypes and paralectotypes being designated. The shell 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 shell morphology as examples, the interspecific differences of Baikalian Cytherissa are shown to not be limited to shell structure. The transformed (geniculate) legs of males of 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, vs the segments are clearly separated in C. latirecta. Taking four species (C. pennata, C. latirecta, Cytherissa sp. 1 and Cytherissa sp. 2) as examples, the structural differences in the hemipenises 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.