Diploneis linearielliptica Metzeltin, Lange-Bertalot & Nergui, 2009

Jovanovska, Elena, Levkov, Zlatko & Edlund, Mark B., 2015, The genus Diploneis Ehrenberg ex Cleve (Bacillariophyta) from Lake Hövsgöl, Mongolia, Phytotaxa 217 (3), pp. 201-248 : 233

Diploneis linearielliptica Metzeltin, Lange-Bertalot & Nergui ( Figs 184–196 )

The valves are linear-elliptical with slightly convex margins and round ends ( Figs 184–191 ). The valve length is 21.0–34.5 μm, and the valve breadth is 7.0–10.5 μm. The axial area is linear to lanceolate, merging with and into a distinctly enlarged round central nodule. From inside, a silica plate covers the whole length of the lanceolate longitudinal canal ( Figs 192, 194 ). The central area is 3.0–4.5 μm wide. From the internal side, the central nodule is raised and distinct ( Figs 192–194 ). The longitudinal canal is narrow and linear, expanded in the middle of the valve, with one row of areolae throughout the whole valve length. From inside the longitudinal canal is covered with a silica plate, forming a “depression” where the raphe is placed ( Figs 192, 194 ). Externally, the raphe is straight and simple, positioned with an expanded depression. Internally, the raphe is straight, inserted in a slightly elevated sternum inside the “depression” formed by the longitudinal canal ( Figs 192, 194 ). The proximal raphe ends are simple and terminate in small drop-like terminal fissures at the margins of the central area, but are not raised onto the central area itself ( Figs 193, 194 ). Distally, the raphe endings are raised into small helictoglossae ( Figs 195, 196 ). The striae are radiate, 15–17 in 10 μm, composed of round areolae, 15–20 in 10 μm. Internally, the alveoli each open via a single oval and continuous opening ( Figs 192, 194 ). This species is characterized with small hyaline area near the longitudinal canal (see arrows on Figs 186, 188 ).

Observations: — Diploneis linearielliptica is described from Mongolian lakes in Khentii province ( Metzeltin et al. 2009). The population from the type locality is characterized by a narrow size range in terms of that observed in Lake Hövsgöl and Arkhangai populations (length: 32.0–46.0 μm vs. 21.0–34.5 μm, breadth: 10.0–14.0 μm vs. 7.0–10.5 μm). The stria density is an additional character that distinguishes these populations (15–17 in 10 μm vs. 11–14 in 10 μm). However, these differences may be the result of an insufficient number of observed valves in the material. SEM analyses of the valve exterior are needed to examine the potential narrow hyaline structure alongside the longitudinal canal.

Ecology and Distribution: —M052A; M166A; M167A; M262A: found in shallow habitats (<1 m depth) in central and southern Lake Hövsgöl and also in streams in Arkhangai province and lakes of Khentii province ( Metzeltin et al. 2009) .

Figures

FIGURES 184–205. LM and SEM internal valve views. Figs 184–196. Diploneis linearielliptica. Figs 184–191. LM valve views. Figs 192, 194. View of the whole valve. Fig. 193. Central area with proximal raphe endings. Figs 195, 196. Distal raphe endings. Figs 197–205. Diploneis aff. fontanella, LM valve views. Scale bars = 10 μm (Figs 184–192, 197–205); 5 μm (Fig. 194); 2 μm (Figs 193, 195, 196).