Diploneis ostracodarum (Pantocsek) Jovanovska, Nakov & Levkov

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 : 20-21

Diploneis ostracodarum (Pantocsek) Jovanovska, Nakov & Levkov ( Figs 12–28 )

Basionym:— Navicula ostracodarum Pantocsek (1892 : pl. 9, fig. 145).

Valves rhombic to elliptical with acute rounded ends. The length of the valve is 36.0–77.0 µm, and the breadth is 23.0– 41.5 µm. The axial area is narrow lanceolate and expanding only closely towards the central area. The central area is 5.3–9.5 µm wide, clearly defined from the axial area. From the outside the longitudinal canal is broadly lanceolate with two, rarely 3 ( Figs 18 , 23–24 ) rows of areola in the middle of the canal, which coalesce into one at the valve apices. Internally, a large lanceolate axial plate covers the longitudinal canal throughout the whole length and continuous with the wide transapical costae. Internally, the longitudinal canal is broad and in the middle of the valve it’s expanded ( Fig. 25 ). The areolae of the longitudinal canal are covered with cribrum ( Figs 23, 24, 27 ). Externally, the raphe is straight with expanded proximal ends that are slightly bent to the same side of the valve ( Fig. 27 ). The raphe distal ends are unilaterally bent at a right angle and to the same side as the proximal ends ( Figs 23, 24, 26 ). Internally, the raphe is straight with simple proximal and distal ends. 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 ( Fig. 25 ). The striae are radial, 8–9 in 10 µm, with round to transapically elongate areolae, 6–10 in 10 µm. The structure of the areolae is very difficult to describe due to valve dissolution of the observed specimens ( Figs 23, 24, 26, 27 ). The internal opening of the alveolus is continuous, spanning the length of the entire chamber ( Figs 25, 28 ). Due to corrosion of the specimens, the fine layers of silica occluding the alveoli from the inside are missing and the areolae become clearly visible inside each alveolus. In the corroded specimens can be noticed the striae uniseriate pattern near the axial area becoming biseriate at the valve margins ( Figs 25, 28 ).

Type:— Căpeni (Köpecz), Neogene fossil deposits in Romania (accession no. BP 88, leg. J. Pantocsek, slide BP 2241, Pantocsek Collection, BP, Lectotype (designated here) = Fig. 14 ; Slide MKNDC 006290 /B, isolectoype) .

Observations:— Jurilj (1954) observed an extant population of D. ostracodarum in Lake Ohrid. In the same publication, he informally proposed transfer to the genus Diploneis based on his discussion of its morphological features ( Jurilj 1954). Recently, Jovanovska et al. (2013) provided the appropriate formal transfer of D. ostracodarum from Navicula to Diploneis .

In Pantocsek's (1892) original description only single measurements of D. ostracodarum were provided (length: 33.5 µm; breadth: 22 µm; striae density: 8–9 in 10 µm). However, Jurilj (1954) in his emended diagnosis gave a broader range of dimensions for D. ostracodarum from Lake Ohrid (length: 30–55 µm; breadth: 20–40 µm; striae density: 6–8 in 10 µm). Such wider ranges have also been documented by Jovanovska et al. (2013) in both surface and core samples from Lake Ohrid (length: 28–66 µm in surface samples and 27–73 µm in core samples; breadth: 17–43 µm in surface samples and 14–45 µm in core samples; striae density: 7–8 in 10 µm in surface samples and 6–8 in 10 µm core samples).

In Pantocsek's original drawing (1892: pl. 9, fig. 145) the longitudinal canal is composed of one row of areolae throughout the whole length. While the longitudinal canal of the lectotype ( Fig. 14 ) designated here and the Lake Ohrid surface and core populations, is composed of two rows of areolae in the middle of the canal, merging into one at the valve apices ( Levkov et al. 2007, Jovanovska et al. 2013). Specimens of D. ostracodarum with one row of areolae throughout the longitudinal canal were not observed in the type material.

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

Distribution:— Căpeni (Köpecz), the Neogene fossil deposit in Romania (fossil, Pantocsek 1892); Finnish Lapland-Scandinavia (fossil, Cleve-Euler 1934); Lake Ohrid in Macedonia (extant, Jovanovska et al. 2013) and Lake Swan in USA (extant, Patrick & Reimer 1966).

Figures

FIGURES 12–22: Diploneis ostracodarum, LM micrographs. Fig. 12. Pantocsek’s original drawing modification from Pantocsek 1892, fig. 9: 145. Fig. 14. Lectotype, BP 2241. Figs 13, 15–22. Valve view. Scale bar = 10 µm.

FIGURES 23–28: Diploneis ostracodarum, SEM micrographs. Fig. 23. External view of the whole valve. Fig. 24. Distal raphe ending with terminal fissures. Fig. 25. Internal view of an entire valve. Fig. 26. External view of corroded valve. Fig. 27. External view of the central area with proximal raphe endings. Fig. 28. Internal view of the central area with proximal raphe endings, showing the structure of the alveoli. Scale bars = 10 µm (Figs 23, 25, 26); 5 µm (Figs 24, 27, 28).