Mallomonas cattiensis E.S. Gusev, H. Doan-Nhu & L. Nguyen-Ngoc, sp. nov. (Figs 2–22)

Cells dimensions unknown. Scales are tripartite, thick. Base plate with small pores. A patch of pores is in the angle of the V-rib (Figs 6, 17–18). Body scales with or without dome, oblong-oval 4.9–6.6 × 2.7–3.4 μm. Shield with 9–13 transverse ribs connected by struts, with a single row of pores between them and with 1–3 depressions (Figs 7, 10, 13). Dome with ribs (Figs 2, 5, 8–10). V-rib acute (Figs 7–10), continuous with the anterior submarginal rib (Fig. 19). Anterior flange with thick secondary layer in form of lobate structures (7–10). Proximal border wide, covering the posterior flange and often overlapping the V-rib. Caudal scales with stout spines (Figs 14–17), 3.5–3.6 × 2.0–2.3 μm. Apical scales are short and asymmetric, 4.1–4.5 × 2.0–2.5 μm (Figs 11, 13). Cysts unknown.

Type: — VIET NAM. Dong Nai Province: Ta Lai reservoir in Cat Tien National Park. 11° 23’ 16” N, 107° 21’ 03” E, E. S. Gusev, 10 th March 2014, SEM stub TL1/2014 (holotype IBIW!, see Fig. 10, sample TL1 10.03.2014, in collection E.S. Gusev. Isotype: SEM stub TL1, sample TL1 10.03.2014, in DMP collection at Oceanographic Museum, Institute of Oceanography, Viet Nam)

Distribution and habitat:— This species was found in the type locality and in a forest stream (11° 23’ 32” N, 107° 22’ 11” E) in Cat Tien National park.

Etymology:— Epithet “cattiensis ” refers to the fact that the species was first found in Cat Tien National Park (Viet Nam).

Observations: Mallomonas cattiensis was found in a Ta Lai reservoir with pH=6.4, low conductivity values (37 μS cm-1) and high temperature (30 °C). Scales of this species were quite abundant in the samples from the reservoir, 4–6 per TEM grid.