Hippodonta subrostrata 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 : 16-17

Hippodonta subrostrata A. Pavlov, Levkov, D.M. Williams & Edlund , sp. nov. ( Figs 166–179 )

Type:— MACEDONIA. Lake Ohrid, Bay of Ohrid, mud + Dreissena , 30 m depth, 15 November 2009, collector Z. Levkov. (Accession No. MKNDC 004294; holotype: slide MKNDC! 004294/1; isotype: slide BM! 101639) .

Valves narrow, lanceolate to elliptic-lanceolate, with long-protracted and acutely rounded valve ends. Valve length 11.5–18.5 µm, width 4.0– 4.6 µm. Axial area narrow-linear, expanding into transverse, 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 discernible in LM, remarkably small. Raphe linear-filiform, with quite weakly pronounced, closely spaced, simple, dot-like central endings. Terminal pores of raphe rarely discernible in LM view, as simple linear and abruptly terminated. Striae finely structured, moderately to strongly radiate at middle, becoming weakly or strongly convergent towards valve ends. Striae evenly spaced throughout, 12–14 in 10 µm. Interstriae of same width as striae, evenly pronounced throughout valve length. Lineolae composing striae barely visible with LM, 3–4 within a stria at middle of valve.

Distribution:— Hippodonta subrostrata has so far only been observed in Lake Ohrid, Macedonia. It occurs on silt substrate on depths larger than 20 m.

Observations:—With respect to valve outline and appearance of the striae, H. subrostrata is similar to H. rostrata (Hust.) Lange-Bert., Metzeltin & Witkowski (1996: 263) depicted in Lange-Bertalot (2001, figs 78: 16) and H. rostratoides (this study, Figs 180–191 ) from Lake Prespa. Nevertheless, H. rostrata has consistently quite longer and markedly narrower protracted valve ends, as well as broader valves when specimens of equal length are compared. In addition, the lineolae composing the striae of H. rostrata are quite broader than the lineolae of H. subrostrata . With regard to the valve outline and the appearance of the striae, H. subrostrata also resembles H. affinis ( Figs 192–200 ) and H. media ( Figs 156–165 ), both from Lake Prespa. Still, the latter two taxa have broader protracted valve ends as compared to the narrow and short protracted ends of H. subrostrata . Hippodonta affinis and H. media are further characterised by broader lineolae than H. subrostrata .

Figures

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.

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.