Mallomonas lusca Gusev & Kezlya, 2021

Gusev, Evgeniy & Kezlya, Elena, 2021, Mallomonas lusca sp. nov. (Synurales, Chrysophyceae) - a rare species from Southeast Asia, Phytotaxa 529 (1), pp. 105-112 : 107-109

Mallomonas lusca Gusev & Kezlya sp. nov. ( Figs. 2–10 )

Cells are armored with apical domed collar scales, domeless body scales, and small rear scales with short spines. The body scales are rhomboidal and slightly asymmetrical, 2.4–3.2 × 1.7–2.6 μm. Shield is patterned with a reticulated meshwork, creating a dense system of irregular, polygonal apertures, and scattered, delicate papillae. The anterior submarginal rib is well developed, raised above the shield, wide, with 9–12 struts at each side. There is a papilla at the distal side of each strut, adjacent to the anterior flange. A small pore is present in most scales near the distal end of the body scales in the apical flange region. The anterior flange is narrow. The posterior submarginal rib is smooth and fused with the arms of the anterior submarginal rib. There are inner struts, joining the posterior submarginal rib and the shield, only visible on TEM images. There is a conspicuous, rounded pit with a raised, thickened, central area (“island”), which is developed in association with the posterior pore in the angle of the posterior submarginal rib. This rounded pit is surrounded by delicate papillae across the border on the shield. Few papillae are present at the thickened, central area (“island”). The posterior border is smooth and encircles half of the scale. The posterior flange is narrow and smooth. The collar scales are 2.6–3.3 × 1.8–2.1 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 similar meshwork pattern to the body scales and an irregular, smooth area near the dome. The dome is oval in outline, with reticulation covering half of the surface, and with a sharply pointed peak at the apex. There are 2–5 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, 1.4–2.2 × 1.2–1.6 μm. Bristles are 4–5 μm in length, curved, smooth and pointed. Cysts were not observed.

Holotype:—Portion of a single gathering of cells on SEM stub number BT_Prud9 (holotype designated here, Figure 2 ) deposited at the Herbarium of the Papanin Institute for Biology of Inland Waters RAS, Borok (IBIW). Material from swamp in Binh Thuan Province, Vietnam. Sample collected 26 April 2014 by E.S. Gusev. Figure 2 is a representative scale from the type specimen.

Type locality:— Vietnam: swamp pool in Binh Thuan Province near Bau Trang Lake, Latitude / Longitude : N11°03.846’ E108°25.836’ .

Etymology:—The epithet “lusca” (single-eyed, monocular) refers to the presence of a rounded pit with a raised thickened central area, resembling an eye.

Distribution: —To date, Mallomonas lusca has been observed in six localities in Vietnam. In addition to the type locality, it has been found in two other waterbodies in Binh Thuan Province and in Khanh Hoa and Dong Nai Provinces ( Table 1 ). Scales of this species were also reported from one locality in Malaysia ( Dürrschmidt & Croome 1985).

Observations: — Mallomonas lusca was found in meso- and eutrophic water bodies within a pH range of 6.0–6.7, specific conductance of 23 to 311 μS cm-1, and temperature 29–34 ºC ( Table 1 ).

Figures

FIGURES 2–10. Mallomonas lusca sp. nov. Figure 2–3. Body scales, SEM. Figures 4–6. Body scales, TEM. Figure 7. Collar scale, TEM. Figure 8. Group of scales with bristles, TEM. Figure 9. Bristle, TEM. Figure 10. Rear scale, TEM. Scales on figures 2, 4–5, 7–10 are from the type locality in Binh Thuan Province; figure 2 is from the holotype specimen. Scale bars: Figures 4–10: 2 μm; Figures 2–3: 0.5 μm.