Hippodonta minuta 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

Hippodonta minuta A. Pavlov, Levkov, D.M. Williams & Edlund , sp. nov. ( Figs 354–364 )

Type:— KENYA. Lake Turkana (former Lake Rudolf), Northern Frontier , 8 th Jan. 1953, sample 1400.1, collector R. Ross. (holotype: slide BM! 1400.1) .

Valves linear-lanceolate, with not protracted, but broadly rounded valve ends. Valve length 12.5–17.0 µm, width 3.5–4.5 µm. Axial area narrow-linear, expanding into a transversely elongated to panduriform central area. Central area forming well-defined fascia. Terminal area clearly distinguishable in LM throughout the size diminution stages, broad and semi-circular in shape. Raphe linear-filiform, with distinct, teardrop-shaped and closely spaced central pores. Terminal pores of raphe distinct, circle-shaped and weakly advancing into the terminal area. Striae coarse, weakly to moderately radiate at the middle, becoming parallel or weakly convergent towards valve ends, 8–12 in 10 µm. Interstriae of equal or lower width than striae. Lineolae composing striae quite densely spaced along a stria, vaguely distinguishable with LM, 3–4 within a stria at the middle of the valve.

Distribution:— Hippodonta minuta has so far only been observed in Lake Turkana, Kenya. In the type material it is very frequent.

Observations:—As with regard to the valve outline and the presence of a fully developed fascia, H. minuta from Lake Turkana, Kenya, most closely resembles H. angustata ( Figs 329–342 ) from Lake Tanganyika. However, H. minuta has stronger pronounced and broader striae, as well as more broadly rounded valve ends. With regard to the valve outline, H. minuta is also similar to H. avittata and H. cf. avittata ( Lange-Bertalot et al. 1996: figs 1: 35–40). Nevertheless, both of the latter taxa have quite small central areas, never a fully developed fascia, while the fascia in H. minuta is consistent throughout the size diminution stages. In addition, the lineolae of H. avittata and H. cf. avittata are clearly discernible with LM in contrast to H. minuta where the lineolae are barely distinguishable.

Figures

FIGURES 308–364: LM micrographs. Figs 308–328. Hippodonta avittatiformis (type material). Figs 327, 328. Images of complete frustules in girdle view. Figs 329–342. Hippodonta angustata (type material). Figs 343–349. Hippodonta cocquytiae (type material). Figs 350–353. Hippodonta conspicua (type material). Figs 354–364. Hippodonta minuta (type material). Fig. 354. Complete frustule in girdle view. Scale bar = 10 µm.