Infraspecies complex of Thalassiosira incerta (Bacillariophyta) from Holocene deposits of Taganrog Bay (Sea of Azov): Thalassiosira incerta var. strelnikovae var. nov. and Thalassiosira incerta var. fluvialis var. nov.

Abstract

New data on the morphology of Thalassiosira incerta, one of the most abundant species of the genus Thalassiosira in the Holocene deposits of the Sea of Azov, are presented. New varieties, T. incerta var. strelnikovae Kovaleva et Gogorev, var. nov. and T. incerta var. fluvialis Gogorev et Kovaleva, var. nov., are described. They are orphologically similar to the type and differ mainly by the presence of a rosette of large areolae around the central fultoportulae and the areolae density on a valve.