Diploneis cf. minuta Petersen

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

Diploneis cf. minuta Petersen ( Figs 254, 255 )

The valves are linear-elliptical with parallel margins and round ends. The valve length is 18.0 μm and the valve breadth is 7.0 μm. The axial area is linear, slightly expanded into a small elongate central area, and also expanded at the valve apices. The central area is elongate, 1.4 μm wide. The longitudinal canal is linear, slightly expanded in the middle of the valve, and composed of one row of areolae throughout the whole length. Externally, the openings of the canal are covered with volate occlusions ( Figs 254, 255 ). At the valve apices the longitudinal canal is extended, circling the distal raphe endings ( Fig. 254 ). The raphe is straight with slightly expanded proximal ends, bent to the same side of the valve ( Fig. 255 ). Distally, the raphe endings are simple and slightly expanded, terminating some distance from the valve mantle ( Fig. 254 ). The striae are parallel, becoming radiate towards the valve apices, 22 in 10 μm. Externally, the alveoli open via a single areola covered with volate occlusions that occupy less than half of the valve width ( Fig. 254 ). The other part of the alveoli is covered by a lanceolate hyaline area, merging with the longitudinal canal ( Fig. 255 ).

Observations: —The population from Lake Hövsgöl is characterized with narrow and linear longitudinal canal very similar to the longitudinal canal of Diploneis minuta Petersen (1928: 381 , fig. 6). In the original description, Petersen gives a single valve measurement for D. minuta (length: 13.0 μm and breadth: 4.4 μm). However, the valve found in Lake Hövsgöl has larger dimensions (length: 18.0 μm and breadth: 7.0 μm), and as such is identified as D. cf. minuta . Unfortunately the lack of additional LM observations makes more detailed comparison rather difficult. The SEM illustrations for D. minuta given in Werum & Lange-Bertalot (2004) nicely fit the population from Lake Hövsgöl. Further LM and SEM analyses are necessary to properly identify this taxon.

Ecology and Distribution: —M276A: found only epilithic at 5 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).