Morphogenesis in Cyclotella ocellata — complex from Lake El’gygytgyn (Chukchi Peninsula) during the Pleistocene-Holocene

The morphology of valves of Cyclotella ocellata from bottom sediments of Lake El’gygytgyn, Chukchi Peninsula, has been studied with help of light and scanning electron microscopes. Considerable variability in the morphology of valves and gradual elimination of forms with big valves were observed upwards the section. The complex evolved by phenotype selection: kuetzingina-morphotype was replaced by ocellatamorphotype and, in the latest Pleistocene, also by arctica-morphotype. Changes in the valve morphology were mainly caused by paleoclimatic fluctuations.