Mallomonas kalmykovae Ignatenko, E.S. Gusev, & Yatsenko-Stepanova, 2025

Ignatenko, Marina, Gusev, Evgeniy & Yatsenko-Stepanova, Tatyana, 2025, Two new species of the genus Mallomonas (Chrysophyceae) from ephemeral pools in the steppe zone of the Southern Urals, Russia, Phytotaxa 705 (1), pp. 86-96 : 88-90

Mallomonas kalmykovae Ignatenko, E.S. Gusev, & Yatsenko-Stepanova sp. nov. ( Figs. 5–15 )

Cells are 12.5–13.0 × 6.0–6.2 μm, armoured with apical domed collar scales, domeless body scales and small rear scales with short spines. The body scales are oval-rhombic, slightly asymmetrical, 3.7–4.7 × 2.2–3.2 μm, with a shield, posterior and anterior submarginal ribs, anterior and posterior flanges, and a posterior rim. The shield is patterned with a reticulated meshwork, creating a dense system of irregular, polygonal apertures and scattered, delicate papillae on the surface. The anterior submarginal rib is raised above the shield, with 10–15 struts on each side, radiating to the anterior flange. There is a papilla at the distal end of each strut near the margin of the anterior flange. The anterior flange is narrow, with struts radiating from the anterior submarginal rib. The posterior submarginal rib is fused with the anterior submarginal rib. The posterior submarginal rib is wide, with internal struts, visible only in TEM images, and with 3 parallel longitudinal ribs on the surface. There are 1 to 4 pits in the angle of the posterior submarginal rib, usually 1 or 2. Each pit contains a small, rimmed base plate pore inside. There are 2-3 rows of meshes on the shield arranged in parallel rows along each arm of the posterior submarginal rib. The posterior rim is wide, smooth, encircles half of the scale, with a depression in the angle. The posterior flange is very narrow and almost invisible. The collar scales are 3.6–4.3 × 2.2–2.6 μm, asymmetrical, elongate and have a broadly rounded, proximal end and narrower distal end, with a well-developed dome. The shield of the collar scales has a meshwork pattern similar to the body scales and smooth area near the dome. The dome is oval in outline, with reticulation, papillae and a sharply pointed peak at the apex. There are several pits with rimmed base plate pores in the angle of the posterior submarginal rib. The rear scales are similar in structure to the body scales but more asymmetrical, bearing small spines and smaller in size, 2.6–2.9 × 1.6–2.0 μm. Bristles are 9.3–10.4 μm in length, slightly curved and pointed. Cysts were not observed.

Holotype (here designated):— Portion of a single gathering of cells on SEM stub 55_I_2 deposited at the Herbarium of the Steppe Institute of the Ural Branch of the Russian Academy of Sciences , Orenburg ( ORIS). Figure 9 is a representative scale from the type specimen.

Type locality:— RUSSIA: Orenburg region, small unnamed ephemeral pool (“Svetlinskii” Biological Reserve). Latitude/Longitude: 51°02′17.4″N, 60°47′15.0″E, 03 May 2023. Leg. M.E. Ignatenko.

Etymology:— The species is named in honor of Olga G. Kalmykova for her significant contribution to the study of the flora of the Southern Urals (Orenburg Region).

Distribution: — In addition to the type locality, this species has been observed in four more localities in Russia: two small ephemeral pools (51°02′19″N, 60°47′09″E and 51°02′18.0″N, 60°48′42.0″E) and Lake Obalykol’ (50°56′13.9″N, 60°44′59.9″E) of the “Svetlinskii” Biological Reserve (Orenburg region, Svetlinskii district), and the ephemeral Lake Nezametnoye (51°01′20.7″N, 61°13′29.9″E) of the “Orenburgskii” State Nature Reserve.

Ecology: —The species has been recorded in small, shallow, ephemeral waterbodies at water temperatures of 12–14 ⁰C and pH of 6.5–7.5.

Figures

FIGURES 5–9. Mallomonas kalmykovae sp. nov. (SEM). Figures 5, 6. Whole cells. Figure 6. Arrows point to pits in the angle of the posterior submarginal rib. Figure 7. Collar and body scales. Figure 8. Body and rear scales. Figure 9. Body scale. Scale bars: figs. 5, 6—5 μm; figs. 7–9—2 μm.

FIGURES 10–15. Mallomonas kalmykovae sp. nov. (TEM). Figures 10–12. Body scales. Figure 13. Collar scale. Figures 14, 15. Rear scales. Scale bars: 1 μm.