Mallomonas sibirica, Bessudova & Firsova & Tomberg & Bayramova & Hilkhanova & Bedoshvili & Bashenkhaeva & Zakharova & Likhoshway, 2023

Bessudova, Anna, Firsova, Alena D., Tomberg, Irina V., Bayramova, Elvira, Hilkhanova, Diana, Bedoshvili, Yekaterina D., Bashenkhaeva, Maria, Zakharova, Lyubov I. Kopyrina Yulia R. & Likhoshway, Yelena V., 2023, Two new species of silica-scaled chrysophytes (Chrysophyceae, Synurales) Mallomonas kicherica and M. sibirica water bodies of Eastern Siberia, Russia, Phytotaxa 620 (1), pp. 59-69 : 64-65

Mallomonas sibirica sp. nov. Bessudova ( Figs. 5–11 )

Description: Scales are 4.1–5.5 × 2.0–2.9 μm, oval, with lateral incurvings. The dome is subcircular, its ornamentation appears to vary between samples: smooth surface or with struts or rounded depressions (up to 0.15 μm in diameter) or reticulum variants were noted. The shield is covered with a thick secondary siliceous layer, marked with 8–12 regularly spaced transverse ribs with rounded depressions between them. Rounded depressions (up to 0.15 μm in diameter) are evenly distributed between the transverse ribs ( Fig. 5, 6, 9 ). There is a pore on the basal plate inside each depression. A group of 8–10 pores is located in the angle of the V-rib in the posterior part of the shield ( Fig. 5 ). This area is lacking the secondary siliceous layer. Anterior flanges are well-developed, with 2–8 (14) struts on each side ( Figs. 7, 8 ). The V-rib on the scales is acutely angled, slightly hooded, and continues on the anterior flanges. The posterior rim is wide and smooth, bears numerous internal struts ( Fig. 5 ). The posterior flange contains approximately 14–20 struts and scattered rounded depressions between them, that are not evenly spaced ( Fig. 5 ). Bristles are 3.3–8.7 μm in length, slightly curved ( Fig. 11 ). The tip is bifurcated with unequal diverging branches. One branch is short and sharp, whereas the other is wide with an acute tip and flat dorsal side. Cysts were not observed.

Holotype (here designated): Portion of a single gathering of cells on SEM stubs No. 18075 deposited at the herbarium of the Limnological Institute, Siberian Branch of the Russian Academy of Sciences, Irkutsk ( LIN). Y.R. Zakharova, Y.D. Bedoshvili and L.I. Kopyrina collected material from Ulu Lake , in the Republic of Yakutia, Russia, on April 24, 2021. Figure 6 illustrates illustrates the characteristic scales from the holotype.

Type locality: Ulu Lake , Republic of Yakutia, Russia. Latitude/Longitude: N63º20ʹ9ʺ E141º3ʹ54ʺ.

Etymology: The new species is named after the region of its origin, Siberia.

Distribution: Up-to-date, M. sibirica have been recorded in the type locality and in other water bodies of Eastern Siberia: мixing zone of Yenisei River and Kara Sea waters; Vorota and Labynkyr lakes, Lake Baikal. M. sibirica was found at wide ranges of environmental parameters: pH from 6.97 to 9.34, specific conductance from 5.17 to 6560 μS̛ сm−1, and temperature of 0.4–10.2°C, salinity from 0.4 to 3.8 ‰ (see Table 1 ).

Figures

FIGURES 5–11. Scales of Mallomonas sibirica sp. nov. from different types of habitats. Figure 5. Body scales with subcircular and smooth dome, evenly spaced transverse ribs and rounded depressions between them. The posterior rim, wide and smooth, bears numerous internal struts. The posterior flange has struts and scattered rounded depressions in the base plate that are not evenly spaced, from Lake Baikal, TEM. Figure 6. Body scale from the type habitat, Lake Ulu, SEM. Figures 7. Body scale, the dome is subcircular, ornamented with struts, undersurface view of the scales, from Lake Labynkyr, SEM. Figures 8. Body scale, the dome is subcircular patterned with rounded depressions, from Lake Labynkyr, SEM. Figure 9. Body scale, from a mixing zone of the Yenisei River and the Kara Sea waters, SEM. Figures 10–11. Body scale, undersurface view of the scales, from Lake Labynkyr, SEM. Scale bars: 2 μm.