Hippodonta conspicua 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 : 25

Hippodonta conspicua A. Pavlov, Levkov, D.M. Williams & Edlund , sp. nov. ( Figs 350–353 )

Type:— TANZANIA. Lake Tanganyika , tangled in trawl from 8 m depth, ¼ mile offshore between Kjiyi and Bangwe, 4 February 1953, collector R. Ross. (holotype: slide BM! 72160; isotype: slide MKNDC! 005850/A) .

Valves broadly elliptic-lanceolate to rhombic-lanceolate, with broadly rounded valve ends that are not protracted. Valve length 14.5–20.0 µm, width 4.5–6.5 µm. Axial area narrow-linear, slightly broadened close to valve centre. Central area small, variable in shape, rhombic or transversely elongated, defined by shortening of one stria from both valve sides. Terminal area clearly distinguishable in LM, broad and lunate. Raphe linear-filiform, with small, teardrop-shaped and closely spaced central pores. Terminal pores of raphe, vaguely discernible in LM, small circle-shaped, weakly advancing into terminal area. Striae coarse, moderately radiate in middle, becoming weakly convergent toward valve apices, evenly spaced throughout, 8–10 in 10 µm. Interstriae of equal or lower width than striae, more pronounced at mid-valve. Lineolae composing striae densely spaced along a stria, not distinguishable in LM.

Distribution:— Hippodonta conspicua has so far only been observed from Lake Tanganyika, East Africa. In the type material it is rare.

Observations:—With regard to the appearance and the pattern of the striae and also the valve outline, H. conspicua is similar to H. cocquytiae ( Figs 343–349 ) also from Lake Tanganyika. Still, the central area of H. cocquytiae is consistently a relatively broad prominent fascia, while the central area of H. conspicua does not expand to the valve margins at the middle of the valve. The differences in the central area of these taxa make a clear and straightforward distinction between the two. With regard to the striae pattern and the shape of the central area, H. conspicua also resembles a taxon named “ Hippodonta (?nov.) spec.” in Metzeltin et al. (2005: figs 59: 37–40). The latter taxon has clearly linear-elliptic valve outline with nearly parallel valve margins in the middle, as compared to the broadly elliptic-lanceolate valves of H. conspicua . Furthermore, in most of the specimens of the taxon in Metzeltin et al. (2005) the lineolae are clearly discernible in LM view, which has not been observed in the case of H. conspicua .

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.