Hippodonta media 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 : 16

Hippodonta media A. Pavlov, Levkov, D.M. Williams & Edlund , sp. nov. ( Figs 156–165 )

Type:— MACEDONIA. Lake Prespa , Bay of Konjsko, mud, 2.5 m depth, 25 May 2003, collector Z. Levkov. (Accession No. MKNDC 000537; holotype: slide MKNDC! 000537/1; isotype: slide BM! 101638) .

Valves elliptic-lanceolate, with not protracted, narrowly rounded to cuneate valve ends. Valve length 12.5–18.0 µm, width 4.0– 5.5 µm. Axial area narrow-linear throughout, expanding into a panduriform central area. Central area forming well-defined fascia, expanding to valve margins at middle of valve and continuously broadened towards margins. Terminal area rarely distinguishable in LM. Raphe linear to weakly curved, filiform, with slightly pronounced, simple, circular central endings. Central pores of raphe mostly closely spaced, distantly positioned only in longer size diminution stages. Terminal pores of raphe rarely discernible in LM, simple, linear and abruptly terminated. Striae coarsely structured, weakly to moderately radiate at middle, becoming parallel or weakly convergent towards valve ends. Striae evenly spaced throughout, 10–12 in 10 µm. Interstriae of equal or lower width than striae. Lineolae composing striae clearly discernible in LM view, 4–6 within a stria at middle of valve.

Distribution:— Hippodonta media has so far only been observed in Lake Prespa, Macedonia. Lake Prespa is a calcareous, meso- to eutrophic lake ( Levkov et al. 2007). This species was rarely observed in deeper littoral sediments (mixture of sand and mud or organic sediment).

Observations:—With respect to valve outline and striae appearance, H. media resembles H. affinis (this study, Figs 192–200 ). Nevertheless, broader valve ends in H. affinis are consistent throughout the size diminution stages, whereas the valve ends of H. media are not clearly protracted. With regard to the valve outline, H. media is somewhat similar to H. subrostrata (this study, Figs 166–179 ) from Lake Ohrid. In comparison to H. subrostrata , H. media has more pronounced lineolae and central raphe endings as well as higher valve width for any given valve length.

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 166–218: LM micrographs. Figs 166–179. Hippodonta subrostrata (type material). Figs 180–191. Hippodonta rostratoides (type material). Figs 192–200. Hippodonta affinis (type material). Figs 201–212. Hippodonta exigua (type material). Figs 213–218. Hippodonta humboldtiana (type material). Scale bar = 10 µm.