Diploneis elliptica (Kützing) Cleve, 1894

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 : 218-219

Diploneis elliptica (Kützing) Cleve ( Figs 54–69 )

Valves are elliptical with convex margins and rounded ends ( Figs 54–61 ). The valve length is 21.0–40.0 μm and the valve breadth is 13.0–21.0 μm. The axial area is linear, slightly expanding towards the central area. The central area is round to slightly transapically elongate, 2.5–5.0 μm wide. From inside a thick lanceolate to rhombic silica plate covers the whole length of the longitudinal canal ( Figs 63, 62 ). Externally, the longitudinal canal is linear and slightly expanded in the middle with one, rarely two rows of areolae ( Figs 65, 66, 68 ). The external openings of the longitudinal canal are covered with cribra similar to those of the striae, from which they are separated with a thick hyaline area ( Figs 65, 66, 68 ). Externally the raphe is straight with expanded proximal ends, bent to the same side of the valve and positioned within a small depression ( Figs 67, 68 ). Distally, the raphe branches end with short terminal fissure some distance from the valve mantle ( Figs 65, 69 ). From inside the raphe is straight, placed in the “depression” formed by the longitudinal canal ( Figs 62, 63 ). The proximal ends reach the height of the canal itself ( Figs 62, 64 ), whereas the distal raphe endings are slightly elevated but not reaching the level of the canal ( Figs 62, 63 ). The striae are radiate in mid-valve becoming strongly radiate towards the valve apices, 8–11 in 10 μm. Externally the alveolate striae are composed of large rectangular to round areolae, 8–15 in 10 μm. Striae are uniseriate, becoming biseriate towards the valve apices and the valve mantle (black arrow on Fig. 69 ). The areolae are occluded by cribra, which are slightly lower than the rest of the non-porous valve surface ( Figs 65, 67, 68 ). Such cribrate depressions are not present at the valve apices (see arrow on Fig. 69 ). Internally the alveoli open via a wide single opening, covered with fine silica layer ( Figs 62–64 ).

Ecology and Distribution: —M063A; M247A; M248A; M262A; M272A; M273A; M274A; M280A; M284A; M287A; M288A; M289A; M290A; M291A; M329A; M330A: widely distributed throughout Lake Hövsgöl on habitats ranging from sand, epipelon, sediments, marl, and epiphytic on Chara .

Figures

FIGURES 54–64. Diploneis elliptica, LM and SEM internal valve views. Figs 54–61. LM valve views. Figs 62, 63. Internal views of the entire valve. Fig. 64. Internal view of the central area with the proximal raphe endings. Scale bars = 10 μm (Figs 54–63); 2 μm (Fig. 64).

FIGURES 65–69. Diploneis elliptica, SEM external valve views. Figs 65, 67. View of the whole valve. Fig. 66. Close view of the cribrate occlusions. Fig. 68. Valve central area with proximal raphe endings. Fig. 69. Distal raphe endings with terminal raphe fissures. Areolae biseriate formation (black arrow on the cribra structure at the valve apices). Scale bars = 10 μm (Figs 65, 67); 2 μm (Figs 66, 68, 69).