Cymbella pamirensis Z.Zhang & Rioual, 2017

Zhang, Zhongyan, Rioual, Patrick, Peng, Yumei, Yang, Xiaoping, Jin, Zhangdong & Ector, Luc, 2017, Cymbella pamirensis sp. nov. (Bacillariophyceae) from an alpine lake in the Pamir Mountains, Northwestern China, Phytotaxa 308 (2), pp. 249-258 : 253

Cymbella pamirensis Z.Zhang & Rioual , sp. nov. ( Figs 2–34 )

LM observations ( Figs 2–28 )

Valves strongly dorsiventral and triangular. Dorsal margin strongly arched. Ventral side nearly straight or slightly concave with slightly tumid center part. Ends variable from broadly round to weakly protracted. Valve dimensions (n=48): length 21 – 39 μm, width 7 – 10.5 μm, length/width ratio 2.6 – 4.3 (median 3.3), curvature value 0.038 – 0.083. Axial area linear, narrow, widening slightly at mid-valve on the dorsal side, almost in the middle of the valve. Central area generally lacking on the ventral side or very small ( Figs 27, 28 ), but present dorsally where striae gradually shortened. Raphe branches lateral, becoming narrower near distal ends ; terminal fissures curved dorsally. Striae moderately radiate in middle of valve. No isolated stigmata discernible under the LM.

Figures

FIGURES 2–28. Cymbella pamirensis. Light micrographs showing variation in size and valve outline. Scale bar: 10 μm. In Fig. 6, l represents chord length and h represents sagitta length.

FIGURES 29–34. Cymbella pamirensis SEM. 29. Valve in external view.30. Close-up on apex in external view.31. Close-up on proximal raphe endings in external view. 32. Valve in internal view. 33. Close-up on central area in internal view, note the three stigmata visible as elongated furrows connected to the striae (arrows) and the discontinuous stria interposed at mid-valve. 34. Close-up on apex in internal view showing the distal raphe fissure ending in helictoglossae and the apical pore field. Scale bars: 10 μm in Figs 29 and 32; 3 μm in Figs 30, 31 and 33; 2 μm in Fig. 34.