Diploneis soninkhishigae, Jovanovska & Levkov & Edlund, 2015

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 : 227-229

Diploneis soninkhishigae sp. nov. ( Figs 135–151 )

The valves are elliptical-lanceolate with convex margins and round ends ( Figs 135–148 ). The valve length is 14.5–24.5 μm, and the valve breadth is 8.0–12.0 μm. The axial area is narrow, linear to lanceolate expanding into a small elongate central area. From inside, a wide linear silica plate covers the longitudinal canal throughout the whole valve length ( Fig. 149 ). The central area is small and elongate, 1.5–2.5 μm wide. Externally, the longitudinal canal is narrow slightly expanded in the middle of the valve with one row of areolae throughout the whole valve length ( Figs 135–148 ). The areolae of the longitudinal canal are covered with cribra similar to the striae ( Fig. 150 ). In the middle of the valve the cribra of the canal are simple, becoming wider and more complex in structure towards the valve apices ( Fig. 148 ). From inside, the longitudinal canal is closed with thick silica plates, forming a “trench” where the raphe is inserted. Externally, the raphe is simple and straight with drop-like proximal ends that are slightly bent, positioned within an expanded depression ( Figs 148, 150 ). Distally, the raphe branches finish with short drop-like terminal fissures, bent to the same side of the valve ( Fig. 148 ). The distal raphe ends terminate some distance from the valve mantle. Internally, the raphe is straight with simple proximal raphe ends, placed in the “trench” formed by the longitudinal canal ( Fig. 149 ). The proximal raphe endings are raised in the central area, while the distal raphe ends are also slightly raised but terminate into small helictoglossae ( Fig. 149 ). Striae are usually uniseriate, becoming biseriate toward the valve margins, 11–15 in 10 μm, and composed of round areolae, 10–15 in 10 μm. Externally, the areolae are covered with cribrate occlusions ( Fig. 150 ), increasing in size towards the valve margins ( Fig. 151 ). From inside, each alveolus opens through a single and continuous opening covered with a thin silica layer ( Fig. 149 ).

Type:— MONGOLIA, Lake Hövsgöl (Hövsgöl National Park). Coordinates : 50°55.056’ N ; 100°37.912’ E, Sediments from 40 m depth (accession number: M248A, M.B. Edlund Collection, Science Museum of Minnesota , collected by Mark B. Edlund and Nergui Soninkhishig, 18 July 1998) (Slide M 248A, ANSP GC-36354 , GCM-24056), holotype, designated here ; example specimens on Figs 136, 137 ; ( Slide 919048, CAS, isotype designated here) .

Etymology:— The species is named in honor of Dr. Nergui Soninkhishig, National University of Mongolia, Botany Faculty, for her pivotal role in developing diatom research in Mongolia and our long friendship.

Observations: — Diploneis soninkhishigae closely resembles Diploneis vetusa Jovanovska, Nakov & Levkov (2013a : figs 106–121), which is characterized with biseriate striae throughout the whole length. In contrast, Diploneis soninkhishigae has uniseriate striae becoming biseriate towards the valve margins. A population of D. soninkhishigae was also observed in Lake Ohrid, Macedonia ( Figs 142–147 ). The striae pattern is more visible in the Lake Ohrid population ( Figs 145, 147 ). D. fontanella has a linear-elliptical valve shape in contrast to the elliptical-lanceolate outline in D. soninkhishigae . In addition, D. fontanella has a higher stria and areola density (striae: 16–18 in 10 μm; areolae: 22–25 in 10 μm), uniseriate striae and a round central area ( Werum & Lange-Bertalot 2004). Diploneis separanda Lange-Bertalot (2004: pl. 76, fig. 1–16; pl. 77, fig. 1–5) is another linear-elliptic taxon, with uniseriate striae becoming biseriate towards the valve margins. However, in addition to differences in valve shape, there are also differences in the stria density (11–15 in 10 μm in D. soninkhishigae vs. 19–21 in 10 μm in D. separanda ) and the areola density (10–12 in 10 μm in D. soninkhishigae vs. 30–35 in 10 μm in D. separanda ). Additionally, SEM images show that the cribrate occlusions in D. soninkhishigae are more numerous and more complex in structure than those in D. separanda (Werum & Lange-Bertalot: 338, pl. 76, figs 16, 15).

Ecology and Distribution: —M248A; M272A; M273A; M274A; M287A; M289A; M291A: found throughout

Lake Hövsgöl in shallow to deep water habitats including marl, sediments, and epipelon.

Figures

FIGURES 135–151. Diploneis soninkhishigae, LM and SEM valve views. Figs 135–141. LM valve views, Lake Hövsgöl. Figs 142–147. LM valve views, Lake Ohrid specimens. Figs 136, 137. Specimens from the holotype slide M248A. Fig. 148. External valve view. Fig. 149. Internal view of the whole valve. Fig. 150. View of the valve central area with proximal raphe ends. Fig. 151. Close-up view of the external openings of the alveolate striae, covered with cribrum. Scale bars = 10 μm (Figs 135–147); 5 μm (Figs 148, 149); 2 μm (Figs 150, 151).