Two new fossil Cyclotella (Kützing) BréBisson species from Lake Ohrid, Ma- cedonia/Albania Slavica Tofilovska 1* , Aleksandra CveTkoska 2 , Elena Jovanovska 3 , Nadja ognJa- nova–Rumenova 4 & Zlatko levkov 1 1 Institute of Biology, Faculty of Natural Sciences, Arhimedova 3, 1000 Skopje, R. Macedonia; *Corresponding author: e–mail: stoflovska@gmail.com 2 Deptartment of Physical Geography, Faculty of Geosciences, Utrecht University, Willem C. van Unnikgebouw 028, Heidelberglaan 2, NL – 3584 CS Utrecht, The Netherlands 3 Department of Animal Ecology and Systematics, Justus–Liebig University, Heinrich–Buff–Ring 26–32, 35392 Giessen, Germany 4 Department of Paleontology, Stratigraphy and Sedimentology, Geological Institute, Bulgarian Academy of Sciences, Acad.G.Bonchev–Street Build. 24, 1113 Sofa, Bulgaria Abstract: Lake Ohrid is the oldest existing lake in Europe and it is known for its high diversity with around 200 endemic or relict diatom species recognized. In order to understand this phenomenon, a large project on deep drilling was performed and a core with maximum sediment depth of 569 m which spans > 1.2 million years was recovered. Two new species of Cyclotella were discovered in the core samples, which are described here as Cyclotella cavitata sp. nov. and Cyclotella sollevata sp. nov. The species have been studied with light and scanning electron microscopes, their morphological features and their relevance to other members of the genus Cyclotella are discussed. Cyclotella cavitata sp. nov. is characterized by round to elliptical shape; elliptic and tangentially undulate central area with one to three papillae on the elevated side. Central fultoportulae are absent while marginal fultoportulae internally are located on slightly depressed costae, with short tube openings with two satellite pores surrounded by cowlings. Satellite pores are situated circumferentially. Internally the rimoportula is situated in the marginal area with a sessile labium. Cyclotella sollevata sp. nov. is characterized by round valves with convex or concave central area which is uneven, colliculate, with papillae and granules. Central fultoportulae are present with variable number (9–21), internally with short tube openings with two satellite pores, which are surrounded by cowlings; Internally marginal fultoportulae are located on depressed costae and have short tube openings with two satellite pores situated circumferentially, surrounded by cowlings. The rimoportulae are located in the marginal area with a sessile labium variably orientated. Cyclotella sollevata and Cyclotella cavitata have been observed only in the fossil sediments of Lake Ohrid. Comments on the position of rimoportula, used as synapomorphic character to separate Lindavia from Cyclotella sensu lato are provided. Key words: Cyclotella, fossil, Lake Ohrid, new species, rimoportula introduction The genus Cyclotella (küTzing) BRéBisson is classified in the family Stephanodiscaceae gleseR & makaRova and represents one of the most frequently cited genera in this family (Houk et al. 2010). Species belonging to Cyclotella are commonly planktonic and mainly fresh- water, a considerably lower number inhabit brackish and marine waters (loginova 1990a, Round et al. 1990; gleseR et al. 1992). Species in Cyclotella have been also frequently recorded in many lacustrine deposits (ognJanova–Rumenova 2001; kHuRseviCH et al. 2001; kHuRseviCH 2006; kHuRseviCH & koCiolek 2008; ko- Ciolek & kHuRseviCH 2013). loginova (1990b) repor- ted that the first representatives from this genus are known from the Late Miocene. Similarly, Temnisko- va–Topalova et al. (1994) showed that the diversity of Cyclotella species in South Europe was higher during 218 Fottea, Olomouc, 16(2): 218–233, 2016 DOI: 10.5507/fot.2016.003