Observations of the genus Cyclotella (Kützing) Brébisson in ancient lakes Ohrid and Prespa and a description of two new species c. paraocellata sp. nov. and C. prespanensis sp. nov

Several taxa from the genus Cyclotella observed in two ancient sister lakes, Prespa and Ohrid were studied and compared to the regionally common species Cyclotella ocellata. Two new species are described from Lake Prespa and additionally Cyclotella thienemannii var. minuscula from Lake Ohrid is formally transferred to Cyclotella minuscula (Jurilj) Cvetkoska stat. nov. Cyclotella paraocellata sp. nov. is compared to C. ocellata and is characterized by a large morphological variability in the fossil and recent diatom assemblages. Cyclotella prespanensis sp. nov. is described and distinguished as a separate taxon by its valve size range, colliculate central area, stria density and number and position of marginal fultoportulae and rimoportulae. The investigation reveals C. ocellata and C. minuscula as the only taxa of the genus Cyclotella present in fossil and contemporary diatom assemblages from both Lake Ohrid and Lake Prespa.