Hippodonta radiata 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 : 22-23

Hippodonta radiata A. Pavlov, Levkov, D.M. Williams & Edlund , sp. nov. ( Figs 291–307 )

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) .

Frustules rectangular in girdle view, somewhat constricted in the middle. Valves of larger specimens lanceolate, rhombic-lanceolate, and elliptic-lanceolate in smaller specimens. Valve ends not protracted, broadly cuneate, acutely rounded in larger specimens and broadly rounded in smaller specimens. Valve length 9.0–30.0 µm, width 3.9–5.9 µm. Axial area narrow-linear throughout. Central area forming well-defined fascia, panduriform or less frequently rectangular in shape. Terminal area distinguishable in LM in most specimens, moderately large, semi-circular or triangular in shape. Raphe linear to weakly curved, filiform. Central raphe endings weakly pronounced, with simple circle-shaped or small teardrop-shaped and closely spaced central pores. Terminal pores of raphe rarely discernible in LM, simple linear or small circle-shaped. Striae coarse, moderately to strongly radiate at middle, becoming parallel or weakly convergent towards valve ends. Striae rarely observed to be nearly parallel at middle of valve. Striae pattern throughout valve length also observable on valve mantle in girdle view ( Fig. 307 ). Striae evenly spaced throughout, 10–12 in 10 µm. Interstriae of lower or equal width to striae. Lineolae composing striae densely spaced within a stria and not discernible in LM.

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

Observations:—With regard to the valve outline as well as the shape of the central area, H. radiata is most closely similar to H. abunda ( Figs 102–137 ) from Lake Ohrid, H. microcostulata ( Figs 482–519 ) from Lake Baikal and H. geocollegarum Lange-Bert., Metzeltin & Witkowski (1996: 255, 256, figs 4: 1–5) from freshwater deposits of the Arkona Basin, Baltic Sea. The striae of H. radiata are coarser, more pronounced and broader than the striae in H. abunda and H. microcostulata . Additionally the central area of the latter two taxa is narrow and rectangular in shape, while in H. radiata the central area is wider and panduriform. The lineolae in H. geocollegarum are clearly discernible in LM view, compared to the densely spaced and not discernible lineolae in H. radiata .

Figures

FIGURES 276–307: LM micrographs. Figs 276–290. Hippodonta crassa (type material). Fig. 290. Complete frustule in girdle view. Figs 291–307. Hippodonta radiata (type material). Fig. 307. Complete frustule in girdle view. Scale bar = 10 µm.

FIGURES 102–165: LM micrographs. Figs 102–137. Hippodonta abunda (type material). Figs 138–155. Hippodonta microcostulata. Figs 156–165. Hippodonta media (type material). Scale bar = 10 µm.

FIGURES 443–498: LM micrographs. Figs 443–469. Hippodonta subelegans. Figs 470–481. Hippodonta acuta (type material). Figs 482–498. Hippodonta microcostulata. Scale bar = 10 µm.

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.