Navicula congqiancuoensis W. Zhang & S. Blanco, 2025

Jiang, Yu-Fei, Blanco, Saúl & Zhang, Wei, 2025, Navicula congqiancuoensis sp. nov. — a new diatom species (Bacillariophyceae) from Sichuan Province, China, PhytoKeys 257, pp. 209-217 : 209-217

Navicula congqiancuoensis W. Zhang & S. Blanco sp. nov.

LM: Figs 1–7 , SEM: Figs 8–13 , 14–18

Description.

Light microscopy (LM) (Figs 1–7 ). The valve is linear to linear-lanceolate, with a slight widening in the center and broadly rounded at the apices, with a length of 42.7–51.2 μm and a width of 4.9–6.1 μm, giving an average L / W ratio 8.2 (40 valves were measured to obtain these size ranges). The raphe is weakly lateral, and the external distal raphe ends are deflected on to the mantle. The striae are radiate and convergent at the ends, and there are two to three short striae in the central area, 14–16 in 10 μm. The axial area is narrow and linear, and the central area is small and elliptical in the central nodule.

Scanning electron microscopy (SEM) (Figs 8 – 18 ). External view: Valves flat. Raphe fissure straight (Figs 8 , 9 ). Proximal raphe endings slightly unilaterally hooked towards secondary valve side. External distal raphe endings curved to the secondary side of valve, with ends positioned on valve mantle (Figs 10 , 12 ). Axial area very narrow and often thickened. Lineolae density ca. 50 in 10 µm (Fig. 11 ). Transversal striae radial, convergent at the ends. The lineolae and the virgae separating them are aligned longitudinally so that there appear to be both longitudinal and transverse striae (Figs 8–13 ). Internal view: the raphe is straight and slightly inclined towards the secondary valve side (Fig. 14 ). On the side of the raphe sternum opposite to central nodule, there is a longitudinal, semilanceolate thickening. Distal raphe endings are well-developed helictoglossae (Figs 15 , 16 ). The accessory rib is well-developed on the primary valve side and unilaterally widened in the center, forming an asymmetrical central nodule that is visible under light microscopy (Figs 17 , 18 ). The Voigt discordance is not visible in the valves we observed.

Type.

China. • Sichuan Province: Tibetan Autonomous Prefecture of Garzi, Daocheng County, Haizishan Nature Reserve, Lake Congqiancuo , 29°21'58"N, 100°04'51"E, elevation 4389 m a. s. l., samples collected by Q. C. ZHOU, 20 Sep. 2018. Holotype CQC 1 #, SHOU! Herbarium of Hydrobiological Department, College of Fisheries and Life Science, Shanghai Ocean University ( SHOU), Shanghai, China = Fig. 3 .

Etymology.

The specific epithet, congqiancuoensis , refers to the locality from which the new species was described.

Ecology.

Navicula congqiancuoensis sp. nov. was found in epilithon samples collected in a high-altitude freshwater lake, with a pH of 8.9–9.4 and very low conductivity of 17.5–17.6 µS / cm. The water temperature at the time of collection was 13.5 ° C, total nitrogen (TN) 0.032–0.043 mg / L, total phosphorus (TP) 0.014–0.016 mg / L.

Figures

Figures 1–7. Navicula congqiancuoensis sp. nov. Size diminution series. Scale bar: 10 μm.

Figures 8–13. Navicula congqiancuoensis sp. nov. SEM external views 8, 9 whole valve showing the outline and external raphe structure 10, 12 distal raphe ends and areolae 11 details of external central area with slightly expanded proximal raphe ends 13 details of external view of striae. Scale bars: 10 μm (8, 9); 2 μm (10, 11, 12, 13).

Figures 14–18. Navicula congqiancuoensis sp. nov. SEM internal views 14 whole valve showing the outline and internal raphe structure 15, 16 distal raphe endings with helictoglossae 17 central area 18 details of areolae. Scale bars: 10 μm (14); 2 μm (15, 16, 17, 18).