Mallomonas uralensis E.S. Gusev, Ignatenko & Yatsenko-Stepanova

Gusev, Evgeniy, Ignatenko, Marina & Yatsenko-Stepanova, Tatyana, 2024, Mallomonas uralensis sp. nov. (Chrysophyceae, Synurales), a new species of the genus Mallomonas from the section Torquatae, Phytotaxa 655 (3), pp. 293-300 : 295

Mallomonas uralensis E.S. Gusev, Ignatenko & Yatsenko-Stepanova sp. nov. ( Figs. 2–13 )

Cell dimensions unknown. Cells are armoured with apical domed collar scales ( Fig. 5 ), domeless body scales ( Figs. 6–9 ) and small rear scales ( Figs. 10–12 ). The body scales are broadly rhomboidal, 2.8–3.7 × 1.9–2.7 µm. The shield is patterned with papillae and small circular pits. The anterior submarginal rib is well developed, raised above the shield, covered with two or three rows of minute papillae at each side. On the outer and inner sides of the anterior submarginal rib there are depressions. Most scales have a small spine at the distal part of the anterior submarginal rib. The anterior flange is narrow, with one row of papillae on each side along the edge of the scale. A pore is located in the distal part of the scale. The posterior submarginal rib is smooth and fused with the arms of the anterior submarginal rib. Along each side of the posterior submarginal rib there are small, rimmed pores on the shield. The posterior rim is narrow and smooth. The posterior flange is narrow and smooth. The rear scales are similar in structure to the body scales, but more asymmetric, bearing stout spines at the anterior end, and smaller in size, 1.4–2.6 × 1.4–2.0 µm. The collar scales are larger than body scales, asymmetrical, elongated and have a broadly rounded proximal end and narrower distal end, 3.8–4.1 × 2.1–2.3 μm. Ornamentation on the shield is the same as found on the body scales. Submarginal ribs are well developed. There are several rows of minute papillae (up to five) on the submarginal rib located at the ventral side of the scale (analogue of the anterior submarginal rib). The submarginal rib on the dorsal side (analogue of the posterior submarginal rib) is smooth. The dome is wide, oval and ornamented with minute papillae. Bristles are up to 9.0 µm long, curved, smooth, tapering to a pointed apex ( Fig. 13 ). Cysts were not observed.

Holotype: —Portion of a single gathering of cells on SEM stub number 55_I_1 deposited at the Herbarium of the Steppe Institute of the Ural Branch of the Russian Academy of Sciences, Orenburg ( ORIS). Material is from the Lake Liman 2 (“Svetlinskii” Biological Reserve ) sampled by M.E. Ignatenko on 03 May 2023. Figure 9 is a representative scale from the type specimen.

Type locality: — RUSSIA: Orenburg region, Lake Liman 2 (“Svetlinskii” Biological Reserve). 51°02ʼ17.4”N, 60°47ʼ15.0”E. 03 May 2023.

Etymology: —the species name derived from “Ural”, the region from which this taxon was described.

Distribution: —To date, M. uralensis has been observed in two neighbouring localities in Russia. In addition to the type locality, it has been found in Lake Zhurmankol (50°58’31.0”N, 61°09’20.1”E), located on the territory of “Orenburgskiy” State Nature Reserve.

Ecology: — M. uralensis was found in small, shallow, ephemeral waterbodies within pH range of 6.5–7.6 and temperature 14.0–14.8 ℃.

Figures

FIGURES 2–4. Mallomonas uralensis sp. nov. (SEM). Figure 2. Whole cells. Figure 3. Group of collar and body scales.Arrows point to minute papillae located on the posterior submarginal rib and flange on the aberrant scale. Figure 4. Group of scales. Figures 2–4: SEM. Note that almost all scales, with the exception of the collar scales, have spines. Scale bars: figs. 2, 3 — 2 μm; fig. 4 — 5 μm.

FIGURES 5–13. Mallomonas uralensis sp. nov. Figure 5. Collar scale. Figures 6–9. Body scales of different shape. Figures 10–12. Rear scales. Figure 13. Bristle and scale (bottom view). Figures 5–7, 9–13: SEM. Figure 8: TEM. Scale bars: fig. 9 — 1 μm; figs. 5–8, 10–13 — 2 μm.