Electron microscopic studies made it possible to describe a new species of diatom for science – Brachysira carabogazgolensis Bulatov sp. nov. (Bacillariophyta) from the mixing zone of the waters of the Kara-Bogaz-Gol hypersaline bay (eastern part of the Caspian Sea). This new species has the following characteristics: the length of the valves is 24.0–34.6 μm, the width is 6.6–7.9 μm, the striae are radial, parallel at the ends of the valve, 26–28 in 10 μm. In the central area, there are two distinct stigmas. For the first time a description of the genus Brachysira Kützing species living in waters with a high salt content of 50‰ is given. Comparison with morphologically similar species showed that B. carabogazgolensis sp. nov. basically has a close morphological similarity to B. vitrea (Grunow) R. Ross, differing from it in: the form of the valve, the presence of two stigmas within the boundaries of the central area, the number of striae on the valve and its ecology.

Keywords: Kara-Bogaz-Gol Bay, Caspian Sea, Bacillariophyta, Brachysira carabogazgolensis sp. nov., salinity, new species

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