The study of phytoplankton in the lakes of the Middle and Southern Urals (Arakul, Elovoe and Bolshie Kasli) using scanning electron microscopy made it possible to detect a small-sized species of diatoms Pantocsekiella comensis that is new for this region. The study of phytoplankton of the lakes of the Middle and Southern Urals (Arakul, Elovoe and Bolshie Kasli) using scanning electron microscopy made it possible to detect a small-sized species of diatoms Pantocsekiella comensis that is new to this region. The study of its morphology in a population from Lake Elovoe showed a coincidence of quantitative (valve diameter, the number of striae in 10 µm, the number of central fultoportulae, the frequency of marginal fultoportulae, the number of lacunae on the valve) and qualitative (valve relief, the presence and location of granules on the valve, the location of lacunae, the orientation of the slit of the rimoportula) features with those of the diagnosis of the species and literature data.