Navicula fuxianturriformis Zhang, Guo, Kociolek & Li, 2022, sp. nov.

Navicula fuxianturriformis Y.-L. Li, J.-S. Guo & Kociolek, sp. nov. (Figs 1–19)

LM (Figs 1–13): Valves lanceolate with cuneate to apiculate apices, nearly symmetrical about the apical axis, with a moderately inflated central portion gradually tapering to the ends. Length 33.5–47.0 µm, width 10.5–12.0 μm, length/width ratio 3.2–3.8, median 3.5 (n = 30). Raphe filiform to slightly lateral. External central raphe ends expanded, appearing as tear drop-like central pores. External terminal raphe fissures short. Axial area narrow-linear, not or slightly expanded proximally. Central area weekly expanded transapically, barely symmetrical, oval-elliptical, with two to five pairs of irregularly shortened striae proximally. Striae nearly parallel at the poles, becoming slightly radiate towards the valve centre, 9–12 in 10 μm. Areolae visible, 36–40 in 10 μm.

SEM: Valve exterior (Figs 14–16): the central raphe ends almost straight with simple drop-like, expanded central pores (Fig. 16). The terminal fissures appear undulate, hooked in opposite directions from one another (Figs 14–15). Striae uniseriate (Figs 14–15). Areolae mostly slit-like, partly round-rectangular around central area (Figs 15–16). Areolae may contain small occlusions (Fig. 16).

Valve interior (Figs 17–19): striae uniseriate, formed by round to rectangular areolae, separated by robust silica ribs (Figs 18–19). Terminal raphe ends offset slightly and terminate in small, knob-like helictoglossae (Fig. 18). Helictoglossae terminate on a small, inwardly projected platform at each apex. Apical areolae rectangular, arranged horizontally and raphe-sternum slightly elevated above the rest of valve (Fig. 19).

Type:— CHINA. Yunnan Province: Fuxian Lake, FXH1, 24°24.870′ N, 102°50.590′ E, elevation 1720 m asl., samples collected by Prof. Yan-Ling Li, 28th March 2005. Holotype FXH200532801 in surficial sediments. Yan-Ling Li, Yunnan University, Kunming, China. Figure 4 is of the holotype.

Etymology:— Specific epithet is compound name referring to the relation of this species to N. turriformis and its type locality in Lake Fuxian.

Ecology:— Navicula fuxianturriformis is known from the surficial sediments, situated at 1720 m a.s.l. At this site, diatom assemblages were dominated by Cyclotella krammeri Håkansson (1990: 261–271), Stephanodiscus hantzschii Grunow (in Cleve et Grunow 1880: 121), Fragilaria crotonensis Kitton (1869: 109–110), Cyclotella rhomboideo - elliptica Skuja (1937: 1–106), Aulacoseira granulata (Ehrenberg) Simonsen (1979: 9–71), Stephanodiscus minutulus (Kützing) Cleve et Möller (1882: 277–324), and several at present unidentified species of Achnanthes Bory de St. - Vincent (1822b) and Amphora Ehrenberg ex Kützing (Kützing 1844: 152).