Navicula daochengensis W. Zhang, Chudaev & T. Wang, 2020

Wang, Ting, Wang, Jia-Lin, Zhou, Qi-Chao, Chudaev, Dmitry A., Kociolek, J. P. & Zhang, Wei, 2020, Navicula daochengensis sp. nov., a new freshwater diatom species (Bacillariophyceae) from a small mountain lake, Sichuan Province, China, Phytotaxa 439 (2), pp. 150-158 : 152-154

Navicula daochengensis W. Zhang, Chudaev & T. Wang sp. nov. ( Figs 1–18 )

LM: Valves narrowly-lanceolate, with subcapitate to broadly rounded ends ( Figs 1–6 ). Length 76.1–100.2 µm, width 10.2–12.7 µm, length to breadth ratio 7.0–8.6 (n= 35). Raphe weakly lateral with distinct external proximal raphe ends, external distal raphe ends deflected onto the mantle. Striae radiate in the central region, becoming parallel round the Voigt discordance, finally convergent towards the apices ( Figs 1–6 ). Striae with apically elongated punctuation, 8–9/ 10 μm in the middle, becoming up to 13/10 μm towards the apices. Axial area very narrow. Central area small, rhombic and slightly asymmetric.

SEM: External valve surface. Raphe fissure straight ( Fig. 7 ). Central raphe endings strongly unilaterally hooked towards secondary valve side ( Figs 8–10 ). Distal raphe endings curved to the secondary side of valve, with ends positioned on valve mantle ( Figs 12, 13 ). Raphe sternum not elevated above the rest of the valve. Axial area very narrow, linear, central area rhombic, slightly asymmetrical. Lineolae connected with narrow, shallow grooves on the interstriae ( Figs 7, 8, 13 ). The poroids and the frets separating them are aligned longitudinally so that there appear to be longitudinal as well as transverse striae ( Figs 10, 11 ). Furthermore, the longitudinal elements formed by the aligned frets are often thickened, so that externally the valve appears as covered by longitudinal ribs of silica ( Fig. 7 ). Lineolae density ca. 35 in 10 µm. Internal valve surface. Raphe fissure straight, slightly inclined to the secondary valve side ( Figs 14, 15 ), shortly interrupted in valve center, central endings straight ( Figs 14–16 ). Accessory rib well developed on the primary valve side, unilaterally widened in the centre, forming asymmetrical central nodule visible in LM ( Fig. 15, 16 ). On the opposite to this central nodule side of raphe sternum also presents longitudinal semilanceolate thickening ( Figs 15, 16 ). Distal raphe endings are well developed helictoglossae ( Figs 17, 18 ). Striae lie in shallow transapical depressions ( Figs 14–18 ). Areolae closed with hymenes ( Fig. 15 ).

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 CQC2#, SHOU! Herbarium of Hydrobiological Department , Shanghai Ocean University ( SHOU), Shanghai.

Etymology: —The specific epithet ‘ daochengensis ’ refers to the locality from which the new species was described.

Figures

FIGURES 1–6. LM micrographs of the type population of Navicula daochengensis in Lake Congqiancuo. Scale bar = 10 μm.

FIGURES 7–13. SEM, External valve views. Fig.7. External view of complete valve. Fig. 8, 9,10. Valve centre exterior. Fig. 11. External view of striae. Fig. 12, 13. External details of the apex. Scale bars = 10 μm (Fig. 7), 2 μm (Figs 8–13)

FIGURES 14–18. SEM, Internal valve views. Fig.14. Internal view of complete valve. Fig. 15, 16. Internal details of the central area. Fig. 17, 18. Valve apices. Scale bars = 10 μm (Fig. 14), 2 μm (Figs 15–18).