Lacustriella provecta Sherbakova, Pomazkina & Rodionova sp. nov.

Light microscopy (LM): (Figs 24–38). Valves linear lanceolate with slightly protracted apiculate apices. Valve length 32–49 μm, width 13–15 μm. External axial area narrow at apices, then gradually expanding towards a weakly defined central area. Raphe filiform, central endings straight, terminal ends bent oppositely. Striae uniseriate, slightly radial becoming radial towards apices, 12–14 in 10 μm. One longitudinal canal along each margin.

Scanning electron microscopy (SEM): (Figs 39–46). Externally, areolae in striae irregular along entire valve surface (from 1 to 4 or several more areolae in a stria), round open, and lay in depressions, 13–20 in 10 μm (Figs 39, 41). Areolae in striae along the border of longitudinal canal slit-like, significantly elongated transapically (Figs 41, 44). The surface of longitudinal canals smooth, unornamented (Fig. 44). Proximal raphe endings lay in slightly elongated drop-shaped depressions (Fig. 41). Distal endings curved towards opposite sides (Fig. 42, 43). Internally, areolae in striae covered with hymenes. Raphe endings terminate on helictoglossae, central helictoglossae merged (Figs 40, 45, 46).

Type: RUSSIA. Lake Baikal: Northern Baikal, Olkhon isl., Cape Khoboi, (53.576111 ºN, 107.8075 ºE), 12 m, sand sample, collected by Sherbakova T.A. on June 18 2021 (holotype: NSK0201992 housed at the Central Siberian Botanical Garden, Novosibirsk, Russia, M.G. Popov Herbarium NSK. Representative type specimen is illustrated in Fig. 25. Isotypes: slide 0014-ВК, Limnological Institute SB RAS, Irkutsk, Russia, station 6, near Anga Bay).

Etymology: the specific epithet provecta means elongated and refers to long areolae near canals.