Diploneis paraparma, 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 : 219-221

Diploneis paraparma sp. nov. ( Figs 70–79 )

Valves are elliptic to linear-elliptic with convex margins and rounded ends ( Figs 70–76, 79 ). The valve length is 19.5–42.0 μm and the valve breadth 12.5–16.5 μm. The axial area is narrow, linear to lanceolate and slightly expanding into a lanceolate and weakly asymmetric central area. From inside a thick silica plate covers the whole length of the longitudinal canal ( Fig. 78 ). The central area is lanceolate and slightly asymmetrical, 1.5–3.0 μm wide. Externally, the longitudinal canal appears narrow, lanceolate to linear and slightly expanded in the middle of the valve. Two rows of areolae open externally, slightly widening into one row of larger areolae towards the valve apices ( Figs 76, 79 ). The external openings of the canal are occluded with cribra ( Figs 76, 77, 79 ), which are open in a depression slightly lower that the rest of the non-porous silica. From inside the longitudinal canal is covered by a thick silica plate ( Fig. 78 ). The heavily siliceous plate forms a “trench” along the whole length of the valve in which the raphe is situated ( Fig. 78 ). From outside the raphe is straight and simple with drop-like proximal ends that are bent to the same side of the valve, positioned with an expanded depression ( Fig. 77 ). Distally, the raphe branches are bent to the same side of the valve into drop-like short terminal fissures ( Figs 76, 79 ). The striae are parallel in mid-valve, becoming radiate towards the distal ends of the valve, 12–15 in 10 μm. Striae are biseriate on the mantle and valve margins, alternately positioned (arrow on Fig. 78 ) and becoming uniseriate toward the axial area. In some valves the biseriate pattern is present throughout the whole striae length ( Figs 71, 75 ). Each stria is composed of small round to elliptical areolae, 15–20 in 10 μm. Externally, the areolae are covered with cribrate occlusions, increasing in size towards the valve margins ( Figs 76, 79 ). Internally, the alveoli open via a single elongate opening covered with a fine silica layer ( Fig. 78 ). The structure of the alveolus can be seen through the fine siliceous layer ( Fig. 78 ).

Type:— MONGOLIA, Lake Hövsgöl (Hövsgöl National Park), south end of lake near Hatgal. Coordinates : 50°25.704’ N ; 100°9.137’ E, epipelon from 0.1 m depth (accession number: M129 A, M.B. Edlund Collection, Science Museum of Minnesota, collected by Mark B. Edlund, Eugene F. Stoermer and Nergui Soninkhishig, 13 June 1996) ( Slide M129A, ANSP GC-36352 , GCM-24054), holotype, designated here ; example specimen on Fig. 70 ; ( Slide 918029, CAS, isotype designated here) .

Etymology:— The species name refers to this taxon’s close relationship and confusion with Diploneis parma .

Observations: — Diploneis paraparma can easily be associated with D. parma . However, the population from Lake Hövsgöl is characterised with an elongated outline compared to the elliptical outline in the D. parma lectotype given by Idei & Kobayasi (1986a: figs 1, 2). Hustedt (1937) depicts two different shapes for D. parma , an elliptic and an elongate-elliptic, arguing that these differences in outline do not merit taxonomic separation. However, the observations of the type material ( Idei & Kobayasi 1986a) did not show specimens with a linear-elliptic form; their analysis of Cleve’s type material showed no relation to later reports for D. parma . It appears that a later D. parma concept has been erroneously perpetuated. Therefore, Hustedt’s concept for two shapes within D. parma is rather questionable because the type material has only a broadly elliptic coarse form. There are no reports for the two different shapes in one locality, and the same is true for Lake Hövsgöl population (this study). Based on historical documentation and our analysis, the concept for two different shapes is poorly supported and therefore we recognize the linear-elliptic form as a new species, Diploneis paraparma . In addition to Hustedt’s misguided and expanded concept, the striae structure is usually reported as uniseriate becoming biseriate towards the valve margins, which was a key feature for further widening the concept of this species. In addition to valve shape differences between D. parma and D. paraparma , morphological differences can be observed in: the structure of the external raphe branches-i) proximal ends (straight without central pores in D. parma vs. straight with drop-like central pores, slightly bent to the same side of the valve in D. paraparma ) and ii) distal ends (deflect and straight in D. parma vs. bent into drop-like short terminal fissures in D. paraparma ); the longitudinal canal (lanceolate expanded in the middle of the valve, composed of one to three areolae in D. parma vs. lanceolate to linear slightly expanded in the middle of the valve, composed of one or two areolae in D. paraparma ); and the valve width (16.0–27.5 μm in D. parma, sensu Idei & Kobayasi 1986a vs. 12.5–16.5 μm in D. paraparma ). Even though D. parma was described from lakes in Finland and Sweden ( Cleve 1891, Idei & Kobayasi 1986a), reports of D. parma exist from different localities worldwide. Some reports likely belong to the now newly described D. paraparma . Further detailed analyses are necessary to ascertain the identity of the many populations widely reported as D. parma .

Ecology and Distribution: —M068A; M077A; M121A; M129A; M248A; M262A; M329A; M331A; M351A: distributed in central and southern Lake Hövsgöl in the sediments, marl, and in epipelic, epilithic, periphytic communities from 10 cm to 40 m depths.

Figures

FIGURES 70–79. Diploneis paraparma, LM and SEM valve views. Figs 70–75. LM valve views. Fig. 70. Specimen from the holotype slide, M129A. Figs 76, 79. External view of the whole valve. Fig. 77. External view of the central area with deflected proximal raphe ends. Fig. 78. Internal view of the entire valve. Scale bars = 10 μm (Figs 70–75); 5 μm (Figs 76, 78, 79); 2 μm (Fig. 77).