Diploneis spectabilis 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 : 232-233

Diploneis spectabilis Metzeltin, Lange-Bertalot & Nergui ( Figs 180–183 )

Valves are elliptical with convex margins and broadly round apices becoming bluntly rounded with the valve size reduction. The valve length is 28.5–38.0 μm, and the valve breadth is 13.0–18.0 μm. The axial area is very narrow and linear, expanding towards the large almost circular to rectangular central area. The central area is 4.5–5.0 μm wide. The longitudinal canal is narrow, linear with a single row of areolae throughout the whole length. The central area is broadly expanded. The raphe is straight and simples, positioned with an expanded depression. Striae are uniseriate and radiate, 18 in 10 μm, composed of round areolae, 20 in 10 μm.

Observations: — Diploneis spectabilis was described from Lake Khangal, Mongolia ( Metzeltin et al. 2009). Observations on the type material were performed in order to ascertain the identity of Arkhangai population. Detailed LM comparisons of the type population and Arkhangai population revealed morphological differences in: valve size (length: 36.0–37.0 μm vs. 28.5–38.0 μm; breadth: 19.0–31.0 μm vs. 13.0–18.0 μm) ; stria density (15–16 in 10 μm vs. 18 in 10 μm); and areola density (16–18 in 10 μm vs. 20 in 10 μm). In Arkhangai materials D. spectabilis was very rare, while in Lake Khangal was quite frequent. The differences in size dimensions might be a result of the small number of specimens in Arkhangai material or ecophenotypic variation. However, in most specimens (there is some variability in valve end shape; compare Fig. 181 with Figs 180, 183 ) the valve outline in Arkhangai’s population fits the original description given by Metzeltin et al. (2009) .

The differences between D. mongolica and D. spectabilis (see Metzeltin et al. 2009) are based on the size range (38.0–58.0 μm vs. 36.0–72.0 μm) and stria density (12.5–14 in 10 μm vs. 15–16 in 10 μm). Additionally, the structure of the longitudinal canal (one row of areolae throughout the whole length in D. spectabilis vs. two to three rows of areolae in the mid-valve narrowing into two to one at the valve apices in D. mongolica ) also separates these species. However, further SEM analyses are necessary to better distinguish differences between D. spectabilis and D. mongolica and within populations of each, and should be supported by additional morphological data.

Ecology and Distribution: —M166A; M167A: examined for comparison, not found in Lake Hövsgöl but more broadly distributed in lakes and streams in Arkhangai and Khentii provinces ( Metzeltin et al. 2009).

Figures

FIGURES 166–183. LM valve views. Figs 166–169. Diploneis elliptica cf. var. ladogensis. Figs 170–172. Diploneis pseudovalis. Figs 173–178. Diploneis subovalis. Fig. 179. Diploneis mongolica. Figs 180–183. Diploneis spectabilis. Scale bar = 10 μm.