Diploneis praeclara (Pantocsek) Cleve-Euler, 1934

Jovanovska, Elena, Buczkó, Krisztina, Ognjanova-Rumenova, Nadja G., Nakov, Teofil & Levkov, Zlatko, 2013, Identity and typification of Diploneis ostracodarum, Diploneis budayana and Diploneis praeclara (Bacillariophyta), Phytotaxa 137 (1), pp. 15-26 : 22-25

Diploneis praeclara (Pantocsek) Cleve-Euler ( Figs 29–43 )

Basionym:— Navicula praeclara Pantocsek (1892 : pl. 11, fig. 182).

Valves elliptical to linear-elliptic with convex margins and bluntly rounded ends. The valve length is 40–74.4 µm, and the breadth is 18–27.1 µm. The axial area is linear and only expanded close to the central area, 4.4–7 µm wide. Externally, the longitudinal canal is linear, expanded in the middle of the valve with two rows of areolae near the central area, which coalesce into one towards the valve apices ( Figs 37, 43 ). Internally a narrow lanceolate axial plate covers the longitudinal canal, continuing into wide transapical costae ( Figs 40, 41 ). From inside the longitudinal canal is narrow and in the middle of the valve is expanded ( Fig. 40 ). The areolae of the longitudinal canal are covered with a cribrum and are morphological identical with the areolae of the striae ( Figs 38, 42, 43 ). From the outside the raphe is straight with expanded proximal ends that are bent with a right angle to the same side of the valve ( Figs 37, 38 ). The distal raphe ends are bent at a 90° angle to the same side of the valve ( Figs 37, 42, 43 ). Internally, the raphe is straight with simple proximal and slightly expanded distal ends ( Figs 40, 41 ). The raphe is place in a “trench” throughout the whole length and only raising to the level of the silica plate in the middle of the valve ( Figs 40, 41 ). The striae are parallel in the middle portion of the valve, becoming radial towards the valve apices, 8–9 in 10 µm. With LM observations the striae appears to be uniseriate ( Figs 30–36 ), although with SEM observations the striae are uniseriate near the center becoming biseriate towards the valve margins ( Figs 39, 42, 43 ). The areolae are large round, 8–11 in 10 µm, externally covered by cribrum ( Figs 38, 42, 43 ). Internally, the alveolus is continuous and in the corroded specimens the structure of the areolae and the striae biseriate pattern becomes clearly visible ( Figs 39–41 ).

Type:— Căpeni (Köpecz), Neogene fossil deposits in Romania (accession no. BP 88, leg. J. Pantocsek, slide BP 2242, Pantocsek Collection, BP, Lectotype (designated here) = Fig. 30 ; Slide MKNDC 006290 /C, isolectoype) .

Observations:— Cleve - Euler (1934) observed fossil specimens of D. praeclara from Scandinavia, and transferred this species into the genus Diploneis (1934: pl. 5, fig. 151). Later, Jurilj (1954) documented an extant population of D. praeclara in Lake Ohrid. With the recent examinations of D. praeclara from Lake Ohrid ( Jovanovska et al. 2013), several morphological differences have been documented between Lake Ohrid and Köpecz populations. The major difference between these two populations is the valve outline. Valves from Lake Ohrid surface and core samples have elliptical to linear - elliptic outline with more or less acute apices compared to Köpecz specimens that generally have bluntly rounded apices. The valve size also separates these two populations: length: 31–39.7 µm vs. 40–74.4 µm; breadth: 16.3–18.3 µm vs. 18–27.1 µm. Both populations fit Jurilj (1954) observations of D. praeclara (length: 35–55 µm and breadth: 15–25 µm). However, Pantocsek (1982) did not specify a size range when describing N. praeclara (only a single measurement is given: length 53 µm, breadth 21 µm), and therefore it is difficult to separate these two populations into separate entities.

The distinguishing feature of D. praeclara is the distinctly biseriate pattern of areolae of the canal in the middle of the valve. This pattern has been noticed in both populations and therefore they are treated as conspecific.

Stratigraphic remarks: — Neogene (late Middle Miocene - early Late Miocene) to present.

Distribution:— Căpeni (Köpecz), Neogene deposits in Romania (fossil, Pantocsek 1892); Finnish Lapland- Scandinavia (fossil, Cleve-Euler 1934) and Lake Ohrid (extant, Jovanovska et al. 2013).

Figures

FIGURES 29–36: Diploneis praeclara, LM micrographs. Fig. 29. Pantocsek’s original drawing modification from Pantocsek 1892, fig. 11: 182. Fig. 30. Lectotype, BP 2242. Figs 31–36. Valve view. Scale bar = 10 µm.

FIGURES 37–43: Diploneis praeclara, SEM micrographs. Fig. 37. External view of corroded valve. Fig. 38. External view of the central area with proximal raphe ending. Fig. 39. Broken valve showing the external and internal valve structure. Fig. 40. Internal view of the whole valve. Fig. 41. Internal view of the valve showing the proximal and distal raphe ends. Fig. 42. Distal raphe ending with terminal fissures. Fig. 43. External valve view. Scale bars = 10 µm (Fig. 43); 5 µm (Figs 37–42).