Abstract
Cyclotella distinguenda Hust. was studied in material from Lake Kournas in the Island of Crete, Greece. It is characterised by a highly variable central area without any processes, a striate zone of varying width with simple alveoli, a single marginal rimoportula. and several marginal fultoportulae. Analyses of the populations reveal two clusters of morphotypes, distinguished by size range and the relative size of the central area, which appears to represent life cycle variation. The affinity of C. distinguenda with other species of Cyclotella is discussed.