Hippodonta certa 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 : 32

Hippodonta certa A. Pavlov, Levkov, D.M. Williams & Edlund , sp. nov. ( Figs 526–534 )

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. Valves elliptic-lanceolate, with weakly protracted and acutely rounded valve ends. The protraction of the valve ends not as clearly pronounced in shorter cell sizes. Valve length 21.0– 36.5 µm, valve breadth 5.0– 6.5 µm. Axial area linear and broad throughout, expanding into prominent, panduriform central area. Central area consistently forming fully developed fascia. Terminal area small, clearly distinguishable with LM, triangular or semi-elliptical in shape. Raphe linear-filiform, with pronounced circular or teardrop-shaped, consistently distantly positioned central pores. Terminal pores of raphe less pronounced than central pores, vaguely discernible with LM, simple linear and weakly advancing into the terminal area. Striae quite coarse, strongly radiate at middle, becoming parallel or weakly convergent towards valve ends, 8–10 in 10 µm. Interstriae of equal or lower width than striae, equally pronounced throughout. Lineolae composing striae clearly discernible with LM, quite large, 4–6 along a stria at middle of valve.

Distribution:— Hippodonta certa has so far only been observed in Lake Baikal, Russia. Frequent in the type locality.

Observations:—Regarding the valve outline and the appearance and pattern of the striae, H. certa most closely resembles H. communis ( Figs 535 – 543 ). The latter taxon can be distinguished based on the lower valve width for any given valve length as well as the lower number of lineolae (3 or 4 within a stria) at the middle of the valve. Hippodonta certa also resembles H. kornevae ( Kulikovskiy et al. 2012: figs 67: 5–12) with regard to the valve outline and the appearance of the striae. Still, the striae pattern at the middle in H. certa is consistently more strongly radiate compared to the nearly parallel striae at the middle in H. kornevae .

Figures

FIGURES 499–546: LM micrographs. Figs 499–519. Hippodonta microcostulata. Figs 520–525. Hippodonta kornevae. Fig. 525. Complete frustule in girdle view. Figs 526–534. Hippodonta certa (type material). Fig. 533. Complete frustule in girdle view. Figs 535–543. Hippodonta communis (type material). Figs 544–546. Hippodonta acus. Scale bar = 10 µm.