Diploneis sp. 1

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 : 240-241

Diploneis sp. 1 ( Figs 256–259 )

The valves are lanceolate-elliptical with slightly convex margins and round ends ( Figs 256, 259 ). The valve length is 13.5– 15.0 μm, and the breadth is 4.0–4.5 μm. The axial area is very narrow and linear toward the central area. The central area is quadratic to slightly rectangular, ca. 0.5 μm wide. The longitudinal canal is narrow and linear, composed of one row of areolae throughout the whole length ( Fig. 259 ). The external openings of the canal are covered with volate occlusions ( Figs 257, 259 ). At the valve apices the areolae of the canal are expanded, and surround the distal raphe endings ( Figs 258, 259 ). Externally, the raphe is straight with expanded small drop-like proximal ends ( Figs 257, 259 ). The distal raphe endings are simple and slightly expanded, terminating some distance from the valve margins ( Figs 258, 259 ). The striae are parallel, becoming slightly radiate at the valve apices, 29–30 in 10 μm. Each alveolate stria opens to the exterior via a single opening covered with volate occlusions that occupy less than half of the valve width ( Fig. 259 ).

Observations: — Diploneis peterseni is the most similar taxon to Diploneis sp. 1 . Diploneis peterseni is characterized by a greater size range (length: 15.0–19.0 μm vs. 13.5–15.0 μm) and a lanceolate hyaline area covering the alveolate striae from the exterior in contrast to a linear hyaline area in Diploneis sp. 1 (compare Fig. 252 with Fig. 259 ). Diploneis minuta closely resembles Diploneis sp. 1 , from which it differs in: valve outline (linear-elliptical with parallel margins vs. lanceolate-elliptical with slightly convex margins); valve size (length: 13.0–18.0 μm vs. 13.5–15.0 μm; breadth: 3.5–4.0 μm vs. 4.0–4.5 μm); and stria density (35 in 10 μm vs. 29–30 in 10 μm). Diploneis oculata differs from Diploneis sp. 1 in stria density (22–24 in 10 μm vs. 29–30 in 10 μm) and valve size (length: 15.0–20.0 μm vs. 13.5–15.0 μm; breadth: 6.0–7.0 μm vs. 4.0–4.5 μm). Taking the valve shape into account, Diploneis marginestriata Hustedt (1922 : pl. 3, fig. 5) morphologically can be allied to Diploneis sp. 1 , from which it differs in the external openings of the alveoli (biseriate simple and round openings vs. volate occlusions).

Similar populations are reported from Lake Ohrid ( Jovanovska et al. 2013a: figs 156–168), and Lake Prespa (Levkov et al. 2007: pl. 124, figs 17–19). Both populations are identified as D. peterseni . However, the detailed analyses on lakes Ohrid, Prespa and Hövsgöl populations show no relation to D. peterseni . In Lake Ohrid, Diploneis sp. 1 seems to be quite frequent in both modern and fossil sediments, while is Lake Hövsgöl is extremely rare and here represented by only two valves.

Ecology and Distribution: —M273A: found only associated with chironomid tubes collected from 4 m depth in northern Lake Hövsgöl.

Figures

FIGURES 253–271. LM and SEM external valve views. Fig. 253. Diploneis cf. eximia, LM valve view. Figs 254, 255. Diploneis cf. minuta, SEM external valve views. Fig. 254. Valve view. Fig. 255. Proximal raphe endings. Figs 256–259. Diploneis sp. 1. Fig. 256. LM valve view. Fig. 257. Central area with proximal raphe endings, SEM. Fig. 258. Distal raphe endings, SEM. Fig. 259. View of the entire valve, SEM. Figs 260–269.Diploneis sp. 2, LM valve views. Fig. 270. Diploneis sp. 3, LM valve view.Fig. 271. Diploneis sp. 3, LM valve view. Scale bars = 10 μm (Figs 253, 256, 260–271); 5 μm (Figs 254, 259); 2 μm (Figs 255, 257, 258).

FIGURES 236–252. LM and SEM external valve views. Figs 236–245.Diploneis oculata. Figs 236–242. LM valve views. Fig. 243. View of the whole valve overlaid by the girdle bands. Fig. 244. View of the entire valve. Fig. 245. Proximal raphe endings and detailed view of the external alveolate openings covered with vola. Fig. 246–252. Diploneis peterseni, LM and SEM external valve views. Figs 246–249. LM valve views. Fig. 250. Valve central area with simple proximal raphe endings. Fig. 251. Distal raphe endings. Fig. 252. View of the entire valve. Scale bars = 10 μm (Figs 236–242, 246–249); 5 μm (Fig. 252); 2 μm (Figs 243–245, 250); 1 μm (Fig. 251).