Diploneis budayana (Pantocsek) Hustedt

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 : 17-20

Diploneis budayana (Pantocsek) Hustedt ( Figs 1–11 )

Basionym:— Navicula budayana Pantocsek (1892 : pl. 4, fig. 57).

Valves elliptical with convex margins and broadly rounded ends. The length of the valve is 58.5‒120.7 µm, and the breadth is 32.1‒54.5 µm. The axial area is lanceolate, narrow near the ends and slightly expanding towards the central area. The central area is 8.7‒12.8 µm wide, slightly expanded and not well defined from the axial area. Externally, the longitudinal canal is broadly lanceolate with one row of round areolae becoming “slit like” at the valve apices ( Figs 7, 11 ). The areolae of the longitudinal canal are covered with projected occlusions alike the striae. From inside, a large rhombic silica plate encloses the longitudinal canal throughout the whole length ( Fig. 8 ). Externally, the raphe is straight with expanded proximal ends ( Fig. 9 ). From the outside the terminal fissures are not enlarged and hooked to the same direction at the transition to the valve mantle ( Figs 7, 9, 11 ). Internally the raphe is straight with simple proximal and somewhat bent distal ends. The raphe is placed in a “trench” throughout the whole length and only raising to the level of the silica plate in the central nodule ( Fig. 8 ). In some specimens from the outside the raphe system is followed by irregularly positioned lines located between the raphe and the row of areolae. These ornamentations are probable result of the corrosion processes rather than real structures ( Figs 3, 5–7, 9, 10, 11 ). The striae, 6‒7 in 10 µm, are parallel in the middle of the valve, becoming radial at the distal ends of the valve. The striae are composed of transapically elongate areolae, 4 in 10 µm ( Figs 1‒6 ). In SEM each areola, opens externally via single transapical line covered with projected occlusions. Alongside the longitudinal canal each single transapical opening has small T-shape ornamentation becoming larger at the valve mantel ( Figs 7, 10, 11 ). In corroded specimens, the structure of the areolae becomes clearly visible ( Fig. 9 ). The alveolus opens to the inside through transverse rows of large oval foramina, 5‒6 in 10 µm ( Fig. 8 ). Internally a narrow pseudoseptum is present at the valve apices ( Fig. 8 ).

Type— Căpeni (Köpecz), Neogene fossil deposits in Romania (accession no. BP 88, leg. J. Pantocsek Slide BP 2240, Pantocsek Collection, BP, Lectotype (designated here) = Fig. 2 ; Slide MKNDC 006290 /A, isolectotype) .

Observations:— In this study population, the valves had wider range of morphological features than given by Pantocsek: length: 95–100 µm vs. 58.5–121.0 µm; breadth: 35–42 µm vs. 32.0– 54.5 µm; striae density: 7–8 in 10 µm vs. 6–7 in 10 µm; areolae density: 5 in 10 µm vs. 4 in 10 µm.

Navicula budayana was illustrated by Pantocsek (1892) but the written description was provided later ( Pantocsek 1905) giving size range of 95–100 µm in length and 35–42 µm in width. Hustedt (1937) formally transferred this species into the genus Diploneis . Later, Jurilj (1954) reported extant population of D. budayana from Lake Ohrid. However, detailed LM and SEM analyses showed several morphological differences between Lake Ohrid and Köpecz populations ( Jovanovska et al. 2013). Based on differences in the valve axial area (wide lanceolate with slightly expanded central area vs. narrow lanceolate with slightly expanded central area) and the striae structure (biseriate vs. single transapical slit), the species from Lake Ohrid was distinguished and described as D. parabudyana ( Jovanovska et al. 2013, figs 1–9, 12, 13). Consequently D. budayana has a limited distribution in the Romanian lacustrine fossil deposits.

With observations on the type material, D. budyana could easily be mistaken with D. hilarula (Pantocsek) Mills (1934: 618) = Navicula hilarula Pantocsek (1892 , fig. 15: 230). However for any given length, specimens of D. hilarula have broader apices and more linear valve margins. Additionally, the most distinguishing feature of D. hilarula is the wide hyaline area position along the longitudinal canal. This hyaline area has not been documented in D. budayana .

Stratigraphic remarks:— Neogene (Middle Miocene - Late Miocene); the intra - Carpathian area became isolated only during the Late Miocene, when the tectonic compression reached to the climax during the Late Sarmatian (~ 11 MY). As a result there was a collision between the “Transylvanian block” and east European Continental plate (Krések & Filipescu 2005). In this realm originated Lake Pannon, which transformed from a large brackish to a freshwater lake ( Magyar et al. 1999). As a part of the Lake Pannon, the Transylvanian Basin represented an isolated basin during the Late Miocene, as indicated by endemic faunas ( Müller et al. 1999). These palaeoecological conditions determined the development of diverse and rich non - marine benthic diatom flora. During the Pliocene the evolution of Baraolt - Brasov Depression could be a remote bay of the Black Sea and having higher salinity due to evaporation ( Krstić et al. 2012). Until now, there has not been enough palaeontological data for more precise chronostratigraphic determination.

Distribution:— Căpeni (Köpecz), Bodos (Bodos) and Bibarczfalva (Baraolt), Neogene fossil deposit in Romania (fossil, Pantocsek 1892).

Figures

FIGURES 1–6: Diploneis budyana, LM micrographs. Fig. 1. Pantocsek’s original drawing modification from Pantocsek 1892, fig. 4: 57. Fig. 2. Lectotype, BP 2240. Figs 3–6. Valve view. Scale bar = 10 µm.

FIGURES 7–11: Diploneis budyana, SEM micrographs. Fig. 7. External view of whole valve. Fig. 8. Internal view of an entire valve, note the pseudoseptum at the valve apices. Fig. 9. External view of corroded valve, showing the structure of the alveoli and the central area with proximal raphe endings. Fig. 10. Showing the structure of the areolar transapical opening covered with projected occlusions. Fig. 11. Distal raphe endings with question mark-shaped terminal fissure. Scale bars = 10 µm (Figs 7–9); 5 µm (Figs 10, 11).