Hippodonta crassa 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

Hippodonta crassa A. Pavlov, Levkov, D.M. Williams & Edlund , sp. nov. ( Figs 276–290 )

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 broadly lanceolate, to rhombic-lanceolate, with not protracted but broadly cuneate valve ends. Valve length 24.5–33.5 µm, width 7.5–9.5 µm. Axial area linear, narrow, expanding into a large, panduriform central area. Central area forming well-defined fascia, expanding to the valve margins. Terminal area clearly distinguishable, moderately large, triangular in shape. Raphe linear, weakly lateral, with weakly pronounced, simple linear or small dot-like central pores. Central pores distantly spaced. Terminal pores of raphe barely discernible with LM, weakly pronounced, simple linear and abruptly terminated. Striae coarse, moderately to strongly radiate at the middle, becoming moderately to strongly convergent near valve ends. Striae evenly spaced throughout, 6–7 in 10 µm. Interstriae quite narrower than the striae. Lineolae composing the striae quite densely spaced within a stria and not clearly discernible in LM.

Distribution:— Hippodonta crassa 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, the appearance of the striae and the shape of the central area H. crassa is most similar to H. costulatiformis var. costulatiformis ( Lange-Bertalot et al. 1996: figs 1: 27–29; this study Figs 45–63 ) and H. costulatiformis var. densistriata ( Figs 69–83 ) from Lake Prespa. In comparison to the latter two taxa, H. crassa has broader and coarser striae, in addition to the consistent panduriform shape of the central area. The central areas of H. costulatiformis var. costulatiformis and H. costulatiformis var. densistriata are weakly panduriform or mostly rectangular.

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 27–63: LM micrographs. Figs 27–44. Hippodonta latelanceolata (type material). Fig. 30. Complete frustule in girdle view. Figs 45–63. Hippodonta costulatiformis var. costulatiformis. Fig. 63. Complete frustule in girdle view. Scale bar = 10 µm.

FIGURES 69–95: LM micrographs. Figs 69–83. Hippodonta costulatiformis var. densistriata (type material). Figs 82, 83. Images of complete frustule in girdle view. Figs 84–95. Hippodonta naviculiformis (type material). Scale bar = 10 µm.