Navicula sparsilineolata Chudaev, Glushchenko, Kulikovskiy & Kociolek sp. nov.

Figs 3, 4

Holotype.

Slide 00962 in collection of Maxim Kulikovskiy at the Herbarium of the Institute of Plant Physiology Russian Academy of Science, Moscow, Russia, represented here by Fig. 3D.

Isotype.

Slide MW-D 899s1 in Diatom collection of the Department of Mycology and Algology, Faculty of Biology, M.V. Lomonosov Moscow State University, Moscow, Russia.

Type locality.

Laos. Champasak Province, Bolaven Plateau, near the Pakse Town, unnamed waterfall, benthos, 15°16.616'N, 106°19.935'E, 1149 m elev., leg. E.L. Konstantinov, 30.11.2011.

Description.

LM (Fig. 3A-N). Valves lanceolate with acutely rounded, non-protracted apices, length 33.9-56.5 μm, width 7.7-9.1 μm (n=31). Axial area narrow, widening towards valve centre, slightly wider on the secondary valve side, central area more or less round, occupying 1/3-1/2 of valve width, margins of raphe-sternum clearly visible as longitudinal lines at the central area. Striae radiate, sometimes (usually in larger valves) becoming parallel at the valve ends, 9.3-10.5/10 μm . Lineolae easy to resolve in light microscope, 17.5-19.7/10 μm . Raphe filiform to narrowly lateral, terminal fissures barely visible, deflected to the secondary valve side, central pores deflected to secondary valve side.

SEM, external view (Fig. 4 A-C). Areolae apically elongate, areolae openings lie in shallow apical grooves more clearly expressed near valve apices (Fig. 4C, white arrows). At each apex two small isolated apical areolae present with shorter slits oriented obliquely or subparallel to valve margin (Fig. 4C, white arrowheads). Raphe-sternum elevated slightly above valve surface in centre, widened, with asymmetrical margins (Fig. 4A, black arrow). Its primary margin slightly convex, secondary margin slightly concave or straight. Central pores drop-like, deflected to secondary side. Each pore possesses small projection in proximal part (Fig. 4B, white arrowheads) and larger triangular insertion in distal part (Fig. 4B, black arrows). Terminal fissures hooked to secondary side (Fig. 4C, black arrow), proximal parts of fissures dilated. On axial area are present thin transapical sutures (Fig. 4B, C, black arrowheads).

SEM, internal view (Fig. 4D-F). Striae wider than virgae, lie at same level as latter, no transapical grooves formed (Fig. 4E, F, black arrows). Internal areola openings occluded with hymens (mostly destroyed) rectangular, wider than external ones (Fig. 4E, black arrows). Raphe slit opens obliquely to secondary side and visible in proximal and distal parts only (Fig. 4E, F, white arrowheads). Raphe-sternum very narrow, widened in centre, flanked with apical grooves from both sides. Accessory rib almost absent, especially in proximal part of valve. Central raphe endings straight, simple (Fig. 4E, black arrowheads). Distal raphe endings well-developed straight helictoglossae (Fig. 4D, F, black arrowheads).

Etymology.

The specific epithet refers to the comparatively low density of areolae in the new species.

Distribution.

Laos. Type locality (unnamed waterfall, slide no 00962) and Tad Yueang Waterfall (slide no 01621).

Ecology.

Navicula sparsilineolata sp. nov. was found in a the waterfalls with low conductivity and circumneutral pH values (Table 1). Below are the dominant species found in the samples along with N. sparsilineolata sp. nov:

Sample 00962: Gomphonema capitatum Ehrenberg, D. confervacea, Luticola burmensis Metzeltin & Levkov, L. nipkowii, P. sikkimensis .

Sample 01621: L. burmensis, L. nipkowii, P. sikkimensis, Platessa oblongella ( Østrup) Wetzel, Lange- Bertalot & Ector.