Navicula yunnanensis Y.Li & Metzeltin, 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 : 141-142

Navicula yunnanensis Y.Li & Metzeltin , nov. spec. ( Figs. 27–32 )

Valvae in toto lanceolatae marginibus plus minusve triundulatis in medio distincte sub apices leviter inflatae. Apices cuneatis denique fere acute rotundatis. Longitudo 98–128 μm, latitudo 18–21 μm. Raphe distincte lateralis poris centralibus et fissuris terminalibus non differentibus. Striae axiales centralesque comparate plus minusve conformantes. Striae transapicales radiantes omnino usque ad apices, 7.0– 7.5 in 10 μm, moderate radiantes in partibus subapicalibus. Lineolae 22–25 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. 24 ).

Description:— Valves, in general, lanceolate with triundulate margins that become less pronounced with decreasing cell size; a prominent inflation in the middle and a weak inflation close to the apices; apices appear cuneate and rather acutely rounded ( Figs. 27–29 ). Length 98–128 μm, breadth 18–21 μm. Raphe distinctly lateral, central pores deflected to the secondary side of the valve. Axial area is moderately narrow, linear. Central area is comparatively much less expanded. Striae radiate throughout. Number of striae is 7.0– 7.5 in 10 μm, more widely spaced in valve center. Lineolae are 22–25 in 10 μm. On valve exterior, sternum is raised, and slightly expanded in the valve centre ( Figs. 28–29 ). The central pores are straight, not elongated, and hardly deflected ( Fig. 28 ). Sternum on valve interior is broad, not interrupted in the valve center; the central pore is scarcely expanded and inclined to the secondary valve side; a central area besides the sternum is lacking ( Figs. 30–32 ).

Distribution:— Known only from Lakes Fuxian and Lugu.

Comments:— As a member of the Navicula hasta complex, N. yunnanensis is distinguished from N. hasta and N. superhasta Lange-Bertalot & Metzeltin (2006: 61) by valve outline and size, striae density, and striae pattern. Valves of N. hasta have lanceolate outline, are 60–95 μm in length, with 8–10 radiate striae in 10 μm, and become gradually more strongly radiate towards the ends. Valves of N. superhasta have lanceolate outline, are 21–25 μm in breadth, with 6–8 radiate striae in 10 μm, and also become gradually more strongly radiate towards the ends. Navicula yunnanensi is similar to N. undulata Skvortzow (1936: 269) in outline, but they differ by size of valve. Valves of N. undulata have 54–72 μm in length, 13–16 in breadth ( Ohtsuka & Tuji 2002).

Figures

FIGURES 27–32. Navicula yunnanensis SEM, external views. 27. Entire external valve view. 28. Central portion of the valve with straight, not elongated, without silicate-tongue and hardly deflected at any direction. 29. View of the end with a slightly curve to the primary side. 30–32. Navicula yunnanensis SEM, internal views. 30. Entire internal valve view. 31. Central nodule with scarcely expanded and a small rounded central area. 32. Helictoglossa slightly offset from raphe terminates.

FIGURES 23–26. Navicula yunnanensis Light microscopy, valve views showing reduction. Fig. 24 is of the holotype.