Occurrence of Cyclotella ambigua Grunow (Bacillariophyta) in the Kuibyshev Reservoir

The long-term study (1989-1995) of phytoplankton from the Kuibyshev Reservoir aided by the scanning electron microscopy revealed a salt water representative of centric diatoms Cyclotella ambigua Grunow, new for the Volga River. Morphological features of the frustule including elements of valve ultrastructure (location and structure of central and marginal fultoportulae, rimoportula, striae) are studied. The similarity and difference from other species of the genus, C. exigua Hakansson, C. striata (Grunow) Grunow, C. scaldensis Muylaert et Sabbe, and C. meneghiniana Kutzing, are shown. Based on original and literature data, the extended diagnosis of C. ambigua is given along with the examination of the ecology and distribution of this species, little known in Russia and abroad.