Hippodonta abunda A. Pavlov, Levkov, D.M. Williams & Edlund, 2013

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 : 15-16

Hippodonta abunda A. Pavlov, Levkov, D.M. Williams & Edlund , sp. nov. ( Figs 102–137 , 219–222 )

Type:— MACEDONIA. Lake Ohrid, Bay of Trpejca , mud + sand, 14 m depth, 2 April 2007, collector Z. Levkov. (Accession No. MKNDC 001212; holotype: slide MKNDC! 001212/1; isotype: slide BM! 101637) .

Valves narrow-rhombic or elliptic-lanceolate, with acutely rounded to cuneate valve ends that are not protracted. In smaller specimens, valve ends become broadly rounded. Valve length 10.0– 20.5 µm, valve width 4.0–5.0 µm. Axial area quite narrow-linear, expanding into a narrow, panduriform central area. Central area forming well-defined fascia, expanding to valve margins at middle of valve. Fascia rarely interrupted by the presence of one shortened stria from both valve sides at middle of valve. Terminal areas quite small and narrow, semi-elliptical in shape. In smaller valves, terminal area weakly discernible in LM. Raphe linearfiliform, with slightly pronounced, closely spaced, simple dot-like central endings. Terminal pores of raphe, when discernible in LM, are simple linear. Striae finely structured, radiate at middle, becoming parallel or weakly convergent towards valve ends. Striae evenly spaced throughout, 12–16 in 10 µ m. Lineolae composing striae distinguishable in LM, 3–5 within a stria.

SEM: Externally, valve face flat ( Fig. 219 ). Terminal area weakly expanding onto valve face. Terminal pores of raphe weakly pronounced, linear, slightly advancing into the terminal area. Central raphe endings quite simple, ending in a simple hole. Striae uniseriate throughout valve face and mantle ( Figs 219, 220 ). Lineolae simple linear and broad, 30 in 10 µm. The rows of lineolae that go around the valve apices are uniseriate ( Figs 219, 220 ). Prominent hyaline area present throughout valve mantle, absent of any structure. Girdle band broad and not ornamented ( Fig. 220 ). Internally, striae positioned in shallow depressions, thus valve face not flat ( Fig. 221 ). Lineolae covered by quite prominent elliptical volae. Central raphe endings simple, linear and distantly positioned. Linear raphe slits distally terminated by weak, semi-circular, helictoglossae. Helictoglossae positioned just before the terminal area and in line with raphe slits. Terminal area strongly pronounced internally ( Fig. 222 ).

Distribution:— Hippodonta abunda has so far only been observed in Lake Ohrid, Macedonia. In the type material it is very frequent.

Observations:—Specimens of Hippodonta abunda have been depicted in Levkov et al. (2007, figs 86: 15–22) but were identified only as “ Hippodonta sp. 3 (?nov)”. Hippodonta abunda closely resembles the population of H. microcostulata (this study, Figs 138–155 ) from Lake Ohrid, with respect to the valve outline. Nevertheless, the striae of H. microcostulata are broader and clearly coarser, as well as less densely spaced (10–12/ 10 µm compared to 12–16/ 10 µm in H. abunda ). Another taxon from Lake Baikal, H. acuta (this study, Figs 470–481 ), strongly resembles H. abunda with respect to valve outline and the fine appearance of the striae. However, the central area of H. acuta is rarely a fully developed fascia and is mostly interrupted by the presence of one shortened stria from both valve sides at the middle of the valve, which is not the case in H. abunda .

Figures

FIGURES 102–165: LM micrographs. Figs 102–137. Hippodonta abunda (type material). Figs 138–155. Hippodonta microcostulata. Figs 156–165. Hippodonta media (type material). Scale bar = 10 µm.

FIGURES 219–225: SEM micrographs. Figs 219–222. Hippodonta abunda (type material). Fig. 219. External view of entire valve. Terminal pores of raphe are simple linear depressions. Fig. 220. External view of complete frustule showing broad, unornamented girdle. Fig. 221. Internal view of entire valve. Striae positioned in shallow depressions, helictoglossae in line with raphe slits. Fig. 222. Close-up of one half of valve, internal view. Lineolae covered by quite prominent elliptical volae. Fig. 223. Hippodonta rostratoides (type material). External view of entire valve. Lineolae quite prominent. Terminal pores of raphe slightly deflected towards one valve side. Fig. 224. Hippodonta affinis (type material). External view of entire valve. Lineolae narrow but long. Terminal pores of raphe simple linear. Fig. 225. Hippodonta exigua (type material). External view of entire valve. Lineolae weakly pronounced, short. Terminal pores of raphe slightly deflected towards one valve side. Scale bars in Figs 219, 223, 224 = 5 µm; Fig. 220 = 2 µm; Fig. 221 = 6 µm; Fig. 222 = 3 µm; Fig. 225 = 4 µm.

FIGURES 443–498: LM micrographs. Figs 443–469. Hippodonta subelegans. Figs 470–481. Hippodonta acuta (type material). Figs 482–498. Hippodonta microcostulata. Scale bar = 10 µm.