Hippodonta pulchra 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 : 26-27

Hippodonta pulchra A. Pavlov, Levkov, D.M. Williams & Edlund , sp. nov. ( Figs 365–372 )

Type:— RUSSIA. Lake Baikal , Tolsky, sediment, 5 m depth, 21 June 1998, collector D.M. Williams. (holotype: slide BM! 100526; isotype: slide MKNDC! 005842/A) .

Frustules rectangular in girdle view, quite broad. Valves broadly rhombic-lanceolate, with cuneate valve ends that are not protracted. Valve length 29.0–43.0 µm, breadth 8.0– 10.5 µm. Axial area narrow-linear, expanding into a narrow-lanceolate, apically elongated central area. Plate-like structure present at the central area, following its shape, crossing the striae ( Figs 367–371 ). Terminal area weakly distinguishable, quite small. Raphe linear, weakly lateral, with distinct, teardrop-shaped and distantly positioned central pores. Terminal pores of raphe distinct, equally pronounced as the central pores, teardrop-shaped and clearly advancing into the terminal area. Striae coarse, moderately to strongly radiate at the middle, becoming strongly convergent near valve ends, 12–14 in 10 µm. Interstriae of lower width than the striae, equally pronounced throughout. Lineolae composing the striae quite densely spaced within a stria, rarely discernible with LM, 5–7 within a stria at the middle of the valve.

Distribution:— Hippodonta pulchra has so far only been observed in Lake Baikal, Russia. This species was observed within the sediment of the lake littoral at shallow depth (5 m). Few other Hippodonta taxa appear at the same locality, namely H. costuloides , H. intermedia (Skab.) Kulikovskiy, Metzeltin & Lange- Bert. in Kulikovskiy et al. (2012: 148, figs 66: 4–10) (≡ Navicula hungarica var. intermedia Skab. ), H. microcostulata and H. subelegans Kulikovskiy, Lange-Bert. & Metzeltin in Kulikovskiy et al. (2012: 156, 157, figs 67: 26–29), with the latter two being of higher abundance.

Observations:—A combination of characters including the coarsely structured, broad and densely spaced striae, remarkably narrow interstriae, and the presence of a clearly observable plate-like structure at the centre of the valve that crosses the striae, make H. pulchra readily distinguishable from other Hippodonta taxa. Nonetheless, specimens of shorter cell sizes of H. lueneburgensis appear slightly similar to H. pulchra with regard to the valve outline. However, the remarkably broad striae, the transverse rectangular central area and absence of additional structures in the central area of H. lueneburgensis make the two taxa clearly distinct.

Figures

FIGURES 365–392: LM micrographs. Figs 365–372. Hippodonta pulchra (type material). Figs 366, 367. Images of same valve at different focus. Fig. 372. Complete frustule in girdle view. Figs 373–376. Hippodonta costuloides. Fig. 373. Image of broken initial cell. Figs 377–392. Hippodonta intermedia. Fig. 380. Complete frustule in girdle view. Scale bar = 10 µm.