Thalassiosira azovica sp. nov. and some other Thalassiosira species (Bacillariophyta) from Holocene sediments of the Sea of Azov

New data on morphology of 10 Thalassiosira species from the Holocene deposits of the Sea of Azov are presented. The new species, Thalassiosira azovica Gogorev et Kovaleva, sp. nov., is described. It is very similar to T. latimarginata and T. trifulta and differs mainly by presence of scattered strutted processes on the valve face. Two species, T. allenii and T. mediterranea, are first recorded for the Sea of Azov and Russia. Furthermore, they are first found in fossils as well as T. incerta and T. proschkinae.