Navicula gongii Metzeltin & Y.Li, 2015

Gong, Zhijun, Metzeltin, Ditmar, Li, Yanling & Edlund, Mark B., 2015, Three new species of Navicula (Bacillariophyta) from lakes in Yunnan Plateau (China), Phytotaxa 208 (2), pp. 135-146 : 138-141

Navicula gongii Metzeltin & Y.Li , nov. spec. ( Figs. 12–22 )

Valvae lanceolatae marginibus distaliter leniter incurvatis ita valvae paulatim protractis apparentibus apicibus comparate obtusius rotundatis. Longitudo 93–127 μm, latitudo 14–17 μm. Ratio longitudo/latitudo = 6. 1–7. 6. Raphe distincte lateralis poris centralibus curvatis distinctius deflexis ad latus secundum valvae. Area axialis aliquid nec angusta nec lata sed angustiora in comparatione. Area centralis minus variabilis formata, fere ampla, rhombica vel aliquid plus transverse dilatata, 2–4 striis abbreviatis utroque. Striae transapicales conspicue minus radiales particulariter in partibus mediis valvarum sed radiales omnino usque ad apices, hic numquam parallelae vel convergentes, mediis striis abbreviatis fortius distanter sitis inter se alteris, 9–11 et sub apices 12–15 in 10 μm. Lineolae circiter 24 in 10 μm.

Type:— CHINA. Yunnan: Lake Fuxian, 24º 24.870’ N, 102º 50.590’ E, 1715 m a.s.l., Y. Li, May 2005 (holotype: praep. Fuxian 46– 1 in coll. Li Yanling, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing, P. R. China, illustrated in Fig. 12 ).

Description:— Valves are rather narrowly lanceolate with long-protracted ends that are comparatively obtusely rounded ( Figs. 12–16 ). Length is 94–127 μm, breadth is 14–17 μm. Length to breadth ratio is 6.1–7.6. Raphe is distinctly lateral, central pores more distinctly deflected to the secondary side of the valve. The axial area appears slightly curved, and comparatively narrow. The central area is less variable, rather large, mostly rhombical or more transversely expanded due to several (2–4) shortened striae which are considerably more widely spaced. Striae are radial throughout but much less radial in proximal parts of valves, with density of 9–11 in 10 μm proximally and 12–15 in 10 μm near the apices. Lineolae are ca. 24 in 10 μm. An elevated asymmetrical sternum is present in SEM ( Fig. 17 ). The central pores are drop-shaped ( Fig. 18 ). Lineolae are connected with narrow, shallow lines on the interstriae ( Figs. 17–19 ). The poroids and the frets separating them are aligned longitudinally so that there appear to be longitudinal as well as transverse striae ( Figs. 18, 19 ). Furthermore the longitudinal elements formed by the aligned frets are often thickened, so that externally the valve appears as is covered by longitudinal ribs of silica ( Figs. 17–19 ). Sternum on valve interior is broad, not interrupted or expanded in the valve center and with raphe branches slightly inclined to the secondary valve side; an axial area beside the sternum is lacking ( Figs. 20–22 ). Raphe-sternum thickened, internal fissures open laterally, except at centre and poles. Raphe terminates at the apices in a curved helictoglossa ( Fig. 22 ).

Distribution:— Known only from Lake Fuxian.

Comments:— Navicula gongii is a member of the N. hasta complex and is distinguished from N. hasta Pantocsek (1892 : figs. 5–74), N. hastata Jurilj (1954: 139) , N. hastatula Lange-Bertalot & Miho in Lange-Bertalot (2001: 39), and similar taxa such as N. parahasta Lange-Bertalot & Miho in Lange-Bertalot (2001: 53) by significantly higher striae density, size of valve, and strongly lateral raphe ( Table 2). Navicula bergeni Hohn (1952: 270) possesses a roughly similar outline, central area, and striae position to N. gongii , but N. bergeni most likely belongs to Craticula , is a brackish taxon, and is broader and longer than N. gongii .

Figures

FIGURES 12–16. Navicula gongii. Light microscopy, valve views showing reduction. Fig. 12 is of the holotype.

FIGURES 17–22. Navicula gongii. SEM, external views. 17. Entire valve view. 18. Central portion of the valve with droplike shaped and lineolae are connected with narrow, shallow lines on the interstriae. 19. View of the end showing distal raphe end deflected onto the valve mantle. 20–22. Navicula gongii. SEM, internal views. 20. Internal valve view with central nodule, raphe slit and helictoglossae. 21. Central nodule with scarcely expanded and inclined to the secondary valve side and a rhombical central area. 22. Helictoglossa slightly offset from raphe terminates.