Light microscopy observations (Figs 2–37): The valves are linear to linear-elliptical with usually linear to convex margins (slightly inflated in the middle) and broadly rounded apices. Valve dimensions (n=50): length 6.1–11.0 μm, width 2.2–3.4 μm. Central area is large, bow-tie-shaped, bordered by several very short striae. The striae are clearly visible in LM, slightly radial (Figs 2–34) and about 20–28 in 10 μm (mainly 24–25). Areolae are not discernible in LM. The axial area is narrow and linear over most of the valve. Raphe is filiform with enlarged proximal raphe endings. The cells present a single H-shaped chloroplast (Figs 35–36). In girdle view, cells are rectangular (Fig. 37). Scanning electron microscopy observations (Figs 38–42): External raphe is straight and the drop-like proximal raphe endings are slightly deflected to the same side. Distal raphe fissures are hooked, bent to the same side of the valve, and extended onto the mantle (Figs 38–39). The striae are biseriate, sometimes uniseriate near the centre of the valve. The striae bordering the central area are generally uniseriate and slightly curved; at the centre shorter striae with only one areola on the valve face can be present (Figs 38, 40–42). Internally, the proximal raphe endings are straight or very slightly deflected and the distal raphe fissure ends in helictoglossa (Figs 41 and 42). Each areola is internally occluded by a hymen (Fig. 41).

Type: — FRANCE. Les Martres-de-Veyre: Font-de-Bleix spring, sample S11_BA_3115, 45° 40’ 52.4” N, 3° 12’ 09.9” E, 332 m a.s.l., A. Beauger, 1 December 2014 (holotype: CLF!, slide no. 104700, here depicted in Figs 2–42; isotypes: CLF! slide no. 104701, BR! slide no. 4435).

Etymology: — The new species, named Sellaphora labernardierei, is dedicated to Dr. Henri Labernardière, geologist, who have a passion for the springs of this longitudinal reach of the Allier River and know all its characteristics.

Ecology and associated diatom taxa: — The type population of S. labernardierei was found in Font-de-Bleix spring associated with other taxa. In December 2014, the two co-dominant taxa were Planothidium lanceolatum (Brébisson ex Kützing 1846: 247) Lange-Bertalot (1999b: 287) (61.5%) with normal and abnormal forms, and S. labernardierei (31.5%). Planothidium frequentissimum (Lange-Bertalot 1993: 4) Lange-Bertalot (1999b: 282) with normal and abnormal forms represented 3.8% of the community. The other taxa (<1%) were: Achnanthidium minutissimum (Kützing 1833: 578) Czarnecki (1994: 157), Craticula riparia (Hustedt 1942: 52) Lange-Bertalot (1993: 14), Crenotia thermalis (Rabenhorst 1864: 107) Wojtal (2013: 81), Diploneis elliptica (Kützing 1844: 98) Cleve (1894: 92), D. separanda Lange-Bert. in Werum & Lange-Bertalot (2004: 144), Encyonopsis cesatii (Rabenhorst 1853: 39) Krammer (1997: 152), Gomphonema lagenula Kützing (1844: 85), G. parvulum Kützing (1849: 65), Nitzschia liebethruthii Rabenhorst (1864: 157), N. linearis W. Smith (1853: 39), and Sellaphora nigri (De Notaris in De Notaris & Baglietto 1872: 296) C.E.Wetzel & Ector in Wetzel et al. (2015: 221). The abnormal forms observed had deformed valve outline (loss of symmetry relative to both axes; abnormal outline as bent) and changes in striation patterns (Falasco et al. 2009a, b).

The spring has a slightly acidic pH (6.4), an elevated conductivity level (1344 μS cm –1) and is enriched with calcium (236.91 mg L –1) (Table 1). The water temperature is around 18°C throughout the year (Labernardière, personal communication). The agricultural activities in the area of the spring caused high concentration in nitrates (32.03 mg L –1). Contrary to other springs from the same area, the lithium concentration is low (<1 mg L –1).