Mallomonas acidophila sp. nov. (Synurales, Chrysophyceae) - a new species from the tropics with morphological features of fossil taxa Author Gusev, Evgeniy 0000-0002-7397-5808 A. N. Severtsov Institute of Ecology and Evolution, Russian Academy of Sciences, Leninsky Prospect 33, 119071 Moscow, Russia & evsergus @ yahoo. com; https: // orcid. org / 0000 - 0002 - 7397 - 5808 evsergus@yahoo.com Author Shkurina, Nataliya 0000-0001-8044-2017 K. A. Timiryazev Institute of Plant Physiology, Russian Academy of Sciences, Botanical Street 35, 127276, Moscow, Russia & shkurrr @ yandex. ru; https: // orcid. org / 0000 - 0001 - 8044 - 2017 shkurrr@yandex.ru Author Huan, Phan Trong 0000-0002-0471-0443 Coastal branch of Joint Vietnam-Russia Tropical Science and Technology Research Center, 30 Nguyen Thien Thuat, Nha Trang 57000, Vietnam & tronghuan 1369 @ yahoo. com; https: // orcid. org / 0000 - 0002 - 0471 - 0443 tronghuan1369@yahoo.com text Phytotaxa 2023 2023-10-13 620 2 157 166 http://dx.doi.org/10.1094/PDIS-04-22-0755-PDN journal article 272447 10.11646/phytotaxa.620.2.3 66d906c7-1f31-41d5-9909-a0cbfa27aa95 1179-3163 10022374 Mallomonas acidophila Gusev & Shkurina ( Figures 2–22 ) Cell dimensions unknown. Scales are tripartite, oval, 4.3–5.6 × 2.4–3.5 μm, with a dome, a V-rib, anterior submarginal ribs, a shield, anterior and posterior flanges, and a posterior rim. The base plate is devoid of pores. The dome is recessed from the distal margin, shallow, elongated or narrowly elliptical, sometimes curved. The dome can be placed perpendicular to the longitudinal axis of the scale or at an angle to this axis. It is covered with papillae. The shield is ornamented with numerous unevenly distributed papillae. The V-rib is rounded, with a broad and U-shaped base, slightly hooded, with arms that are continuous with the anterior submarginal ribs. The anterior submarginal ribs are of equal length if the dome is perpendicular to the longitudinal axis or unequal if the dome is located at an angle to the longitudinal axis. The anterior flanges are narrow. The posterior rim is narrow and encircles one-third to one-half of the scale perimeter. The posterior flange is wide and smooth. It lacks a secondary siliceous layer in a narrow area along the posterior rim and is strongly thickened in the area adjacent to the V-rib. Bristles are 2.4–7.2 μm long, straight, with a hook-shaped flattened foot, turned at an angle of approximately 45 degrees or less relative to the shaft, gutter-shaped bristle shaft, and a flattened and bifurcated apical tip with a wide, rounded middle part. Cysts are unknown. Holotype ( designated here ) :— Portion of a single gathering of cells on SEM stub number TTH55 deposited at the Herbarium of the Papanin Institute for Biology of Inland Waters RAS , Borok ( IBIW ). Material from unnamed reservoir in Thua Thien Hue Province , Vietnam . Sample collected 28 October 2022 by E. Gusev. Figure 3 is a representative scale from the type specimen. Type locality:— Vietnam : unnamed swamp water body in Thua Thien Hue Province , Phong Điễn District , Latitude / Longitude : N16°39.777’ E107°21.905’ . Etymology :—The epithet “acidophila” refers to the fact that this species is found at low pH values. Distribution: —To date, M . acidophila has been observed in two neighbouring localities in Vietnam . In addition to the type locality, it has been found in another unnamed water body (Latitude/Longitude: N16°39.694’ E107°21.746’ ). Observations: — Mallomonas acidophila was found in acidic conditions (pH 5.0–5.2), with low specific conductance values ranged from 17 to 18 μS cm-1 , temperature 26 ºC, total phosphorus concentrations 68–133 μL-1 , Kjeldahl nitrogen concentrations 406–508 μL-1 .