Morphology, taxonomical position, and distribution of the genera of diatoms Ochigma and Khursevichia from Lake Baikal

Resumo

The morphology of the genera of diatoms Ochigma and Khursevichia based on new data from LM and SEM is discussed. The genera have been described from Lake Baikal. The morphology of raphe and pore occlusions resembles those in cymbelloid diatoms. We suggest including these genera in the order Cymbellales and the family Cymbellaceae. The role of different morphological features that are important for the taxonomy is discussed. Symmetry plays a minor role in diatom taxonomy. The morphology of raphe and pore occlusions is the most important factor. Pore occlusions within the genus Khursevichia belong to the tectulum type. Pore occlusions within the genus Ochigma are more complicated: they are represented by a tectulum inside and a foricula outside. The broadened description of the species Ochigma dubiosa is given.