Hippodonta humboldtiana 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 : 19-20

Hippodonta humboldtiana A. Pavlov, Levkov, D.M. Williams & Edlund , sp. nov. ( Figs 213–218 )

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! 101643) .

Valves rhombic-lanceolate, with distinctly protracted and narrowly rounded valve ends. Valve length 15.7–17.7 µm, width 4.5–6.0 µm. Axial area quite narrow-linear, expanding into a small, rhombic or apicallyelongated elliptic central area. Central area defined by continuous shortening of striae from both valve sides. Terminal area not clearly discernible in LM. Raphe linear-filiform, with clearly pronounced, elliptic central endings. Central raphe endings distantly positioned. Terminal pores of raphe rarely distinguishable in LM view, simple and abruptly terminated. Striae coarse, weakly radiate at middle, becoming parallel or weakly convergent towards valve ends. Striae evenly and densely spaced throughout, 16 in 10 µ m. Interstriae remarkably narrow. Lineolae composing striae not discernible in LM.

Distribution:— Hippodonta humboldtiana has so far only been observed in Lake Ohrid, Macedonia, where it occurs in the sediment at depths from 20– 35 m.

Observations:—With respect to the valve outline and its broadly protracted valve ends, H. humboldtiana is similar to H. arkonensis Lange-Bert., Metzeltin & Witkowski (1996: 252, 253, figs 4: 11–17), which was described as fossil, from freshwater deposits, in the Arkona Basin of the Baltic Sea. Nevertheless, H. humboldtiana is consistently wider for any given valve length.

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.