Hippodonta hungarica (Grunow) Lange-Bert., Metzeltin & Witkowski

Pavlov, Aleksandar, Levkov, Zlatko, Williams, David M. & Edlund, Mark B., 2013, Observations on Hippodonta (Bacillariophyceae) in selected ancient lakes, Phytotaxa 90 (1), pp. 1-53 : 21-22

Hippodonta hungarica (Grunow) Lange-Bert., Metzeltin & Witkowski ( Figs 239–248 , 274, 275 )

Valves narrow-lanceolate to rhombic-lanceolate, with slightly protracted and broadly rounded valve ends. Valve length 12.0– 18.5 µm, width 4.5–6.5 µm. Axial area narrow-linear throughout, weakly expanding into small rhombic central area, defined by shortening of one central stria from both valve sides. Terminal area clearly distinguishable in LM, narrow, lunate and cap-like. Raphe linear-filiform, with weakly pronounced, small teardrop-shaped and closely spaced central endings. Terminal pores of raphe clearly discernible in LM, equally pronounced as the central endings, teardrop-shaped, rarely simple linear. Terminal pores of raphe positioned before terminal area or weakly advancing into it, slightly curved towards one valve side. Striae coarse, weakly to moderately radiate in the middle, becoming parallel or weakly convergent towards valve ends, evenly spaced throughout, 10 in 10 µm. Interstriae consistently with lower width than striae. In longer valves interstriae more pronounced than in shorter size diminution stages. Lineolae composing striae quite densely spaced within a stria, not discernible in LM.

SEM: Externally, valve face flat ( Figs 274, 275 ). Terminal area weakly expanding onto valve face. Terminal pores of raphe distinct, weakly advancing into terminal area and slightly deflected towards one valve side. Central raphe endings strongly pronounced, teardrop-shaped depressions. Striae biseriate, lineolae quite small, simple linear and alternating along a stria, c. 40 in 10 µm. Rows of areolae that go around the valve apices biseriate ( Fig. 275 ).

Distribution:—Specimens in the population of H. hungarica from Lake Dojran match the concept in the protologue of Navicula hungarica Grunow (1860 : fig. 1: 30). With respect to specimens found in ancient lakes, H. hungarica has only been observed in Lake Dojran, Macedonia. Lake Dojran is shallow, highly eutrophic lake ( Levkov & Stojanovski 2002) with a high abundance of macrophytes in the littoral. Hippodonta hungarica was frequently observed in epiphytic communities, usually in the summer period. The species was observed also in ancient Lake Hövsgöl, Mongolia ( Edlund et al. 2001, 2006b).

Observations:— Hippodonta hungarica resembles H. uruguayensis ( Metzeltin et al. 2005: figs 59: 15–29), a species described from Blanca Lagoon and found in few other lagoons in Uruguay. In the protologue of H. uruguayensis , the authors use the lower valve width as a main differential character between the two species. Additionally, Metzeltin et al. (2005) point out that the biogeographical occurrence would support the delimitation of two populations as separate species, European and South-American. Furthermore, the valve ends of H. uruguayensis are never protracted and the valves are more linear lanceolate, as compared to the weakly protracted valve ends and more rhombic-lanceolate valves in H. hungarica .

Hippodonta linearis (Østrup) Lange-Bert., Metzeltin & Witkowski (1996: 261, 262, figs 1: 16–21; 2: 3–4; 4: 24) ( Figs 249–271 )

Navicula hungarica var. linearis Østrup 1910: 79 , fig. 2: 53

Valves linear-elliptic, with valve margins nearly parallel in most specimens examined. Valve ends not protracted, broadly rounded. Valve length 12.9–22.2 µ m, width 5.5–7.0 µ m. Axial area narrow-linear throughout, expanding into transversely elongated central area, defined by shortening of one stria from both valve sides, at middle of valve. Usually, central striae more distantly spaced. Terminal area clearly distinguishable in LM, broad and cap-like. Raphe weakly curved, filiform, with moderately pronounced, teardrop-shaped, consistently closely spaced central pores. Terminal pores of raphe clearly discernible in LM view, equally or less pronounced than central pores, teardrop-shaped. Terminal pores of raphe strongly advancing into terminal area, rarely observed as ending before, clearly curved towards one valve side. Striae coarse, moderately to strongly radiate at middle, becoming parallel or weakly convergent towards valve ends, 10–12 in 10 µm. Lineolae clearly distinguishable in LM view, densely spaced within a stria, 7–8 per stria at middle of valve.

Distribution:—During this study, Hippodonta linearis was observed only in Lake Dojran, Macedonia, in the same habitats as H. hungarica . According to Lange-Bertalot (2001) it is widespread in brackish waters or freshwaters with high conductivity; similar ecological preferences were given by Witkowski et al. (2000).

Observations:— The morphology of H. linearis observed from Lake Dojran corresponds quite well with the specimens of the type material from the Østrup Collection (C) depicted in Lange-Bertalot et al. (1996: figs 1:16, 17) .

Figures

FIGURES 226–271: LM micrographs. Figs 226–238. Hippodonta capitata. Figs 239–248. Hippodonta hungarica. Figs 249–271. Hippodonta linearis. Scale bar = 10 µm.

FIGURES 272–275: SEM micrographs. Figs 272, 273. Hippodonta capitata. Fig. 272. External view of entire valve. Striae biseriate throughout. Terminal pores of raphe slightly deflected towards secondary valve side. Fig. 273. Internal view of entire valve. Striae composed of two or three lines of pores, positioned in quite broad depressions. Raphe sternum thickened towards central raphe endings. Helictoglossae positioned just before terminal area, not advancing into it. Figs 274, 275. External view of entire valves of Hippodonta hungarica. Striae biseriate throughout; lineolae quite small; terminal pores of raphe weakly deflected towards secondary valve side. Scale bars in Figs 272–275 = 5 µm.