Mallomonas croomei E.S. Gusev, Shkurina, Hoan Tran & Martynenko, 2025

Gusev, Evgeniy S., Shkurina, Nataliya A., Tran, Hoan & Martynenko, Nikita A., 2025, Revision of the Mallomonas splendens species clade (Chrysophyceae, Synurales) based on morphological and molecular data, Phytotaxa 708 (3), pp. 241-259 : 247-250

Mallomonas croomei E.S. Gusev, Shkurina, Hoan Tran & Martynenko sp. nov. ( Figs 11–18 )

Cells are elongated, cylindrical or ellipsoidal, 21–28 × 8–15 µm, covered with three types of scales (anterior, body and posterior), and with up to four bristles on each end of the cell. All scales are thick, with an internal reticulation of closely-spaced meshes and externally covered with papillae. Body scales are rhomboidal, slightly asymmetrical, 5.5– 7.1 × 3.6–5.1 µm. The V-rib is absent. The posterior rim is wide, encircles approximately half of the scale perimeter. Posterior and anterior flanges are narrow and smooth. The shield is thick and raised above the flanges. On the shield, along the posterior flange, there is an area without papillae, where the scales overlap each other. Anterior scales are oval, 4.7–5.6 × 6.8–7.8 µm, with a curved zigzag-like rib, wide posterior rim and posterior flange. Posterior scales are broadly ovate, asymmetrical, 6.1–7.3 × 4.6–7.8 µm, with an asymmetrically placed dome and a curved posterior submarginal rib along the posterior rim. Bristles are straight or slightly curved, 7.3–17.3 µm, with a flattened foot, an open slit on the shaft, terminates with small teeth. Stomatocysts unknown.

Holotype: — Portion of a single gathering of cells on SEM stub 61_I_1, deposited at the Herbarium of the Steppe Institute of the Ural Branch of the Russian Academy of Sciences , Orenburg ( ORIS). Material from Ta Lai reservoir, Cat Tien National Park, Dong Nai Province, Vietnam, collected by E.S. Gusev, 26 June 2019.

Type locality: — Vietnam: Ta Lai reservoir, Cat Tien National Park, Dong Nai Province, Latitude/Longitude: N11° 23.267’ E107° 21.050’.

Genbank accession numbers for the reference strain (919P): PV771126 (nuclear SSU rDNA), PV780773 (rbc L cpDNA) and PV779686 (nuclear ITS rDNA).

Etymology:—the epithet is in honor of the well-known specialist in limnology and phycology Roger L. Croome, who is the author of the many new Mallomonas taxa.

Distribution and ecology:—In addition to the type locality, this species has been observed in eleven more localities in Vietnam ( Tables 1, 2). Mallomonas croomei was found at wide ranges of environmental parameters: pH from 4.6 to 7.4, specific conductance from 6 to 80 µS cm-1, and temperature 21–36 ºC, but tend to prefer acidic conditions with low mineralized waters ( Tables 1, 2).

Figures

FIGURES 11–18. Mallomonas croomei sp. nov. (strain 919P) studied using TEM and SEM. Figures 11–13. Body scales, TEM. Figures 14–15. Body scales, SEM. Figure 16. Posterior scale, SEM. Figure 17. Whole cell with bristles, SEM. Figure 18. Bristle, TEM. Scale bars: Figures 14–15: 1 μm; Figures 11–13, 16: 2 μm; Figures 17–18: 5 μm.