Paraplaconeis dorofeyukae Glushchenko, Mironov, Nergui & Kulikovskiy 2025, sp. nov.

Paraplaconeis dorofeyukae Glushchenko, Mironov, Nergui & Kulikovskiy sp. nov. (Figs 2–45) LM description (Figs 2–19, 26–39):— Valves lanceolate-elliptical. Valve dimensions: length 30.3–33.5 µm, width 12.6–13.6 µm in wild population; length 31.3–32.6 µm, width 11.9–13.0 µm (cultures). Ends rostrate, 2.1–2.9 µm wide in wild population; 2.1–2.5 µm wide in culture. Axial area narrow, weakly expanded to the central area. Central area transapically expanded, nearly rhomboid, ca. 1/3 of the valve breadth, formed by 3–4 shortened striae on each side, sometimes very short intercalary striae are present. Raphe filiform. Central raphe ends are slightly widened and drop-shaped. Distal raphe ends deflected to the valve margin. Striae at the central part of the valve are parallel, radiate to the apices, 11–13 in the 10 µm. Areolae undiscernible in LM. SEM, external view (Figs 20–21, 40–42):— Valve face is almost flat, the striae are slightly deeper relative to the interstriae (Fig. 41, white arrows). These deepenings become nearly inconspicuous at the apices (Fig. 42, white arrows). The raphe is weakly eccentric. The central raphe ends are expanded (Fig. 41, black arrows) slightly deflected in different directions (better noticeable in LM). Distal raphe ends unilaterally deflected. One fissure is simple (Figs 21, 40, black arrows), another is recurved (Fig. 21, 40, white arrows). Striae mostly comprised of two rows of areolae, arranged in quincunx (Fig. 41, black arrowheads); the striae bordering the central sometimes become single-rowed towards the central part of the valve (Fig. 41, white arrowheads). Striae also become uniseriate at the valve margin (Fig. 42, white arrowheads). Areolae density 70–80 in 10 µm. SEM, internal view (Figs 22–25, 43–45):— The raphe slits are straight. Central raphe ends are hook-shaped (Figs 24, 44, black arrows). Distal raphe ends equipped with small helictoglossae, which are slightly deflected in the opposite directions at separate ends (Figs 23, 25, 43, 45, white arrows). Helictoglossae are located in the small hyaline area, near the adjacent striae (Figs 25, 45, asterisks). The striae are deepened into the valve face. The interstriae are noticeably wider than the striae (Figs 24, 44, white arrows). The areolae of the distichous striae are separated by vimines, forming a honeycomb-like arrangement (Figs 24–25, white arrowheads). The areolae of the uniseriate striae are separated by simple vimines with perpendicular struts (Fig. 24, black arrowheads). Areolae occluded by foriculotectula, represented by spear-shaped to nearly reniform outgrowths (Figs 25, 45, black arrowheads). Valve apices possess two groups of subpolar areolae, having the same structure as the transapical areolae (Fig. 25, black arrows). Type:— Mongolia, Arkhangai Province, Tariat District, Undor Tsohen-Nuur Lake (48°05.892’N 099°12.407’E); leg. M.S. Kulikovskiy in 07 July 2015. Slide no. 03291 from oxidized culture strain no. Mnp 217, isolated from sample Mn 075, deposited in the herbarium of MHA, Main Botanical Garden, Russian Academy of Science, Moscow, Russia. Holotype specimen illustrated in Fig. 10. Isotype:— Slide no. 03291a, deposited in the collection of Maxim Kulikovskiy at the Herbarium of the Institute of Plant Physiology Russian Academy of Sciences, Moscow, Russia. Representative specimens:— Strains Mnp17 (slides 03291, 03291a), Mnp219 (slide 03282); sample Mn075 (slide 03112). Reference strains:— Mnp217 and Mnp219, isolated from the sample Mn075, deposited in the collection of Maxim Kulikovskiy at the Herbarium of the Institute of Plant Physiology, Russian Academy of Sciences, Moscow, Russia. Sequence data. Partial SSU rRNA gene sequences, V4 region (GenBank accession number PQ662630 for strain Mnp217, PQ662631 for strain Mnp219); partial rbcL sequences (GenBank accession number PQ736508 for strain Mnp217, PQ736509 for strain Mnp219). Etymology: —The specific epithet is dedicated to Dr N.I. Dorofeyuk, a prominent Russian algologist, for her contribution to understanding the diatoms of Mongolia. Distribution:— As yet known only from the type locality. Ecology:— The species was discovered in a phytoplankton sample with alkaline pH (9.11), temperature—17 °C, and moderate salt content (TDS= 158 mg /l).