Mallomonas fragariformis, Gusev & Kapustin & Shkurina & Martynenko & Huan, 2022

Gusev, Evgeniy, Kapustin, Dmitry, Shkurina, Nataliya, Martynenko, Nikita & Huan, Phan Trong, 2022, Mallomonas fragariformis sp. nov. (Synurales, Chrysophyceae), a new tropical chrysophyte species, Phytotaxa 576 (1), pp. 123-130 : 125-127

Mallomonas fragariformis sp. nov. Gusev, Kapustin, Shkurina, Martynenko ( Figures 2–17 )

Three types of scales have been observed: apical domed collar scales, domeless body scales and small rear scales with stout four-edged spines. The body scales are rhomboidal and slightly asymmetric, 2.7–4.1 × 1.9–2.7 μm ( Figures 2–4 , 12–16 ). Shield and anterior flanges are ornamented with numerous densely spaced large papillae which are placed in shallow pits, rounded or hexagonal, formed by a surface thickening of the secondary siliceous layer ( Figure 5 ). Anterior flanges are slightly raised above the shield. The shield is patterned with an inner reticulated meshwork, creating a dense system of irregular, polygonal or rounded apertures, covered by surface siliceous layer and visible only with TEM ( Figures 12–16 ). Posterior submarginal rib is well developed while arms of anterior submarginal rib are weakly developed or absent. At the distal end of each arm of the posterior submarginal rib, another short rib may develop on the outer side. There is a rounded or triangular area in the angle of the posterior submarginal rib, lacking secondary layer, which contains from 3 to more than 10 rimmed pores on the base plate. Posterior border is wide and smooth, with inner struts, encircles half of the scale. Posterior flange is narrow. The collar scales are asymmetrical, elongate, and have a broadly rounded proximal end and narrower distal end, 4.1–4.4 × 2.3–2.4 μm ( Figures 9–10 ). Ornamentation on the shield and flanges is the same as found on the body scales. The posterior submarginal rib on the “dorsal” side is well developed, connected with the dome. An additional submarginal rib (anterior) departs from the dome on the “ventral” side. The dome on the collar scales is partially ornamented with papillae, and has a sharply pointed peak at the apex. There are up to 6 rimmed base plate pores in the angle of the posterior submarginal rib. The rear scales are 1.6–2.9 × 1.3–1.9 μm, similar in structure and outline to the body scales, and each scale bearing stout four-edged spine ( Figures 6–7 , 11 ). These spines are 1.1–1.2 µm long, located at the distal ends of the scales or, more often, shifted to the right side, near the distal end. The spines gradually taper from the base to the top (basal width 0.39–0.55 µm and apical width 0.07–0.17 µm); on top there is a strongly narrowed and slightly drawn part with a rim of teeth at the top. All four edges of the spine are serrated. Bristles are short, 6–10 µm long, curved, smooth ( Figure 17 ). Cysts were not observed.

Holotype (here designated): Portion of a single gathering of cells on SEM stub No. PQ7 (holotype designated here in Figure 4 ) deposited at the Herbarium, Papanin Institute for Biology of Inland Waters RAS, Borok ( IBIW). Material from unnamed pond in the northwest part of Phú Quốc Island , Kiên Giang Province, Viet Nam, collected by E.S. Gusev on the 25 th of April, 2015. Figure 4 is a representative scale from the specimen .

Type Locality: Pond in the northwest part of Phú Qu ốc Island, Kiên Giang Province, Viet Nam. Latitude / Longitude : N10° 19.856’, E103° 51.538’ .

Etymology: the species epithet means “strawberry-like” and reflects the similarity between scale ornamentation (large papillae located in shallow pits) and strawberry fruit.

Distribution: In addition to the type locality, this species has been observed in other regions of Viet Nam: another pond in Phú Quốc Island, aquaculture pond on Côn Sõn Island, unnamed reservoir and water body in Bình Thuận Province, swamp area Suối Bun in Phú Yên Province, pond in Quảng Trị Province, and Bàu Sen Lake in Thừa Thiên Huễ Province ( Table 1 ). Also, Mallomonas fragariformis has previously been reported from Java Island in Indonesia as M. sp. 1 (Kapustin & Gusev 2019, figs 9,10, p. 15). Mallomonas fragariformis was found at wide ranges of environmental parameters: pH from 6.0 to 8.66, specific conductance from 37 to 329 µS cm-1, chlorophyll a values from 50 to 87 µg l –1, and temperature 30–36 ºC ( Table 1 ).

Figures

FIGURES 2–8. Mallomonas fragariformis sp. nov. Figures 2–5. Body scales, SEM. Figure 5. Close-up view of the scale ornamentation. Figure 6. Rear scale with a small spine, SEM. Figure 7. Group of rear scales, SEM. Note the spines with four serrated edges. Figure 8. Group of body and rear scales, TEM. Scale bars: Figures 2–7: 1 μm; Figure 8: 2 μm.

FIGURES 9–17. Mallomonas fragariformis sp. nov. Figures 9, 10. Collar scales. Figure 9. SEM. Figure 10. TEM. Figure 11. Body and rear scales, TEM. Figures 12–16. Body scales, TEM. Figure 17. Group of scales and bristles. Scale bars: Figures 9, 12, 14: 1 μm; Figures 10–11, 13, 15–17: 2 μm.