Resurrection of the diatom genus Stephanocyclus (Coscinodiscophyceae: Stephanodiscaceae) on the basis of an integrated molecular and morphological approach

: The history of the description and subsequent consideration of the diatom genus Stephanocyclus Skabitschevsky (Thalassiosirales, Bacillariophyta) is discussed. The new genus was described on the basis of a new species, S. planum Skabitschevsky, originally collected from the River Ob. However, the genus has been more or less forgotten since its initial description in 1975. Type material from Skabitschevsky’s collection has subsequently been lost. An epitype for this species is recognized from the same region as the original collection, and typified with a population from Lake Baikal and using molecular data. The population from Lake Baikal fully corresponds in terms of morphological features with the population originally investigated by Skabitschevsky. Morphology of the genus Stephanocyclus is discussed and, on the basis of an integrated molecular and morphological investigation, we propose to recognize the genus, including four species within it. Three taxa are transferred to the genus, including Cyclotella cryptica , C. gamma and C. meneghiniana. A comparison of Stephanocyclus with other cyclotelloid genera is given.