Two New Species, Mallomonas baicalensis sp. nov. and M. grachevii sp. nov. (Synurales Chrysophyceae), Found under the Ice of Lake Baikal

Two new species of silica-scaled chrysophytes (order Synurales) from the genus Mallomonas and sections Striatae Mallomonas baicalensis sp. nov. and M. grachevii sp. nov. found at the bottom surface of the ice of Lake Baikal, with a structure of siliceous scales, are described using electron microscopy. The main and unique distinctive feature of M. baicalensis is its dome with a long spine and the slightly asymmetrical shape of its scales, regardless of their position on the cell. We could not find the bristles, and if there are spines on the dome, we can assume that they may be missing. The main distinguishing feature of M. grachevii is the presence of a secondary layer on the shield except at the angle of the V-rib, in which an area without the secondary layer, a "window", is present with numerous pores, and the first transverse rib closest to the dome is thickened. Among the Mallomonas species from the section Striatae, only M. siveri and M. baicalensis have a group of rimmed pores in the corner of the V-rib. As a result of our research, the number of Mallomonas species of the section Striatae found in Lake Baikal has increased to eight, of which, in addition to the new species, only one species is widespread, and the rest are rare, previously foundin oligotrophic/mountain water bodies.