France

France (fr)

Région Nouvelle Aquitaine

Département de la Haute-Vienne

River Ardour at Folles village

 s.c.

2017-7-24

46° 6' 18'' N ; 1° 27' 17.964'' E

46.105 ; 1.45499

LM : Frustules in girdle view narrow, rectangular (Fig. 69). Valves strictly lanceolate to occasionally weakly rhombic–lanceolate in larger valves. Smaller valves more elliptic–lanceolate. Valve margins clearly convex, gradually narrowing towards the non–protracted, acutely to cuneately rounded apices. Valve dimensions (n=20): length 27–48 μm, width 8–9.5 μm. Axial area narrow, linear, weakly widening at the central area. Central area distinct, usually slightly asym- metric, more or less rounded or occasionally elliptical, bordered by irregularly shortened central striae. Raphe weakly curved with slightly expanded, almost straight central endings. Terminal fissures hardly discernible in LM. Striae strongly radiate becoming parallel to slightly convergent at the apices, 10–11 in 10μm. Lineolae well discernible in LM. SEM : Raphe sternum externally very weakly raised (Figs 70, 72), asymmetrically widened at the central area (Fig. 72). Raphe branches straight to weakly curved, slightly eccentric (Figs 70, 71). Central raphe endings almost straight to unilaterally slightly deflected towards the secondary side. Central raphe pores slightly drop–like expanded. Terminal raphe fissures unilaterally hooked towards the secondary side (Fig. 73). Voigt discordance clearly developed (Fig. 73). Striae uniseriate, composed of very long lineolae, almost twice as long as the virgae, 30–33 in 10 μm. Lineolae becoming narrower towards the apices (Fig. 73). Internally, raphe running weakly lateral of the raphe sternum with the raphe slit opening on the side (Fig. 74). Sternum weakly but distinctly widened at the central area (Fig. 75). Central raphe endings located in the middle of the central area (Fig. 75). Helictoglossae small (Fig. 76). Lineolae internally covered by individual hymenes (Figs 75, 76)

River periphyton