Nitzschia tabellaria (Grunow) Grunow

Liu, Qi, Wu, Weiwei, Wang, Jie, Feng, Jia, Lv, Junping, Kociolek, John Patrick & Xie, Shulian, 2017, Valve ultrastructure of Nitzschia shanxiensis nom. nov., stat. nov. and N. tabellaria (Bacillariales, Bacillariophyceae), with comments on their systematic position, Phytotaxa 312 (2), pp. 228-236 : 231-233

Nitzschia tabellaria (Grunow) Grunow in Cleve & Grunow 1880

( Figs 13–24 , 31–36 ).

Synonyms: N. sinuata var. tabellaria (Grunow) Grunow in Van Heurck 1881; Grunowia tabellaria (Grunow) Rabenhorst 1864 Basionym : Denticula tabellaria Grunow 1862: 548

Specimens from China occur as solitary frustules. Valves are rhomboid to lanceolate with a broadly rounded margin at the center and round apices. The raphe is situated in a strongly eccentric keel. The fibulae are clearly visible, elongate and occupy about one-half the valve surface, numbering 6–8 in 10 μm. Valve length is 11.5–20.0 μm and breadth is 5.0–7.0 μm (n=20). Uniseriate striae are distinctly punctate, parallel around the center to nearly radiate towards the ends, often 3–4 striae occur between fibulae. Fibulae number 22–23 in 10 μm. The fibulate raphe systems occur on the opposite sides of the frustule.

Distribution and ecology of the Chinese specimens: —In Shanxi province, Niangziguan spring basin, China, pH 8.2, temperature 17°C; collected in Lake Pingyang attached to a large stone.

Observations: —In SEM, valves have a distinct central inflation and taper to narrowly-rounded apices ( Fig. 31 ). Externally, striae are composed of individual, circular to elongate areolae with small occlusions ( Fig. 31 ). The keel is a simple ridge extending marginally from apex to apex ( Fig. 31 ). The raphe is filiform and without central raphe ending ( Fig. 32 ). The distal raphe ends are clearly hooked towards the same side of the valve ( Figs 31, 33 ).

Internally, uniseriate striae are composed of individual elongate simple pores ( Fig. 35 ). The canal raphe is subtended by fibulae extending about one-half the valve surface ( Fig. 34 ). The canal raphe opens to the valve interior through a series of elliptical portulae ( Fig. 35 ). A central nodule is absent ( Fig. 35 ). The distal raphe ends terminate as helictoglossae and are positioned on the mantle at the apex ( Figs 34, 36 ).

Figures

FIGURES 1–24. LM micrographs of Nitzschia shanxiensis and Nitzschia tabellaria. 1–12: Nitzschia shanxiensis. 13–24: Nitzschia tabellaria. Scale bar: 10 μm.

FIGURES 31–36. SEM micrographs of Nitzschia tabellaria. 31. External view of the valve, showing the swollen valve with a simple ridged keel. 32. Central area showing the raphe is filiform and without central raphe ending. 33. Valve terminus showing the hooked raphe ends. 34. Internal view of the valve, showing the canal raphe subtended by fibulae. 35. Internal view of valve center showing the fibulae structures. 36. Distal raphe ends showing helictoglossae and are positioned on the mantle at the apices.