Aude Beauger
email: aude.beauger@uca.fr

Elisabeth Allain
email: elisabeth.allain@uca.fr

Olivier Voldoire
email: olivier.voldoire@uca.fr

Christelle Blavignac
email: christelle.blavignac@uca.fr

Sofia Rossi
email: sofia.rossi4961@gmail.com

Carlos E Wetzel
email: carlos.wetzel@list.lu

Luc Ector
email: ector@list.lu

Gomphosphenia vallei (Bacillariophyta), a new diatom species from a stream in the "Réserve Naturelle Nationale de la Vallée de Chaudefour

Keywords: crystalline area, Europe, Gomphosphenia, headwaters, new species, ultrastructure

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Introduction

The genus Gomphosphenia Lange-Bertalot (1995: 243) was separated from Gomphonema Ehrenberg (1832: 87) by several ultrastructural features including transapically elongated areolae and T-shaped internal central raphe fissures, while lacking an apical pore field, isolated stigma, and the deflected terminal raphe fissures found in Gomphonema. The type species of the genus is Gomphosphenia lingulatiformis (Lange-Bertalot & E.Reichardt in Lange-Bertalot 1993: 60) Lange-Bertalot (1995: 242).

Gomphosphenia species have been observed in diverse types of habitats such as rivers [START_REF] Van De Vijver | New and interesting diatom species (Bacillariophyceae) from Swedish rivers[END_REF], Saber et al. 2021), lakes [START_REF] Kociolek | Diatoms of the United States, 1 Taxonomy, ultrastructure and descriptions of new species and other rarely reported taxa from lake sediments in the western U.S.A[END_REF][START_REF] Genkal | Gomphosphenia stoermeri Kociolek et Thomas (Bacillariophyta) is a new species for the flora of Russia[END_REF][START_REF] Gligora Udovič | Gomphosphaenia plenkoviciae sp. nov. A new species from Crveno jezero, Croatia[END_REF], Ohtsuka et al. 2018), carbonate springs in karst landscapes (Werum & Lange-Bertalot 2004[START_REF] Straub | Biodiversité en Ville de Neuchâtel : Diatomées et autres organismes microscopiques[END_REF][START_REF] Dedić | The first report on periphytic diatoms on artificial and natural substrate in the karstic spring Bunica, Bosnia and Herzegovina[END_REF][START_REF] Peeters | Quelques diatomées des sources du territoire bourguignon[END_REF], and artificial habitats like drainage channels of dams [START_REF] Noga | The inside of a dam as an unusual habitat for two rare species of Gomphosphenia -G. fontinalis and G. holmquistii[END_REF]. For many species of Gomphosphenia, individuals were observed from cold oligotrophic and alkaline waters such as G. stoermeri Kociolek & E.W.Thomas in Thomas et al. (2009: 230). Gomphosphenia fontinalis Lange-Bertalot, Ector & Werum in Werum & Lange-Bertalot (2004: 163) is apparently restricted to calcium-bicarbonate-rich springs, eutrophic and even α-mesosaprobic, with moderate electric conductivity (Werum & Lange-Bertalot 2004[START_REF] Lange-Bertalot | Freshwater benthic diatoms of Central Europe: over 800 common species used in ecological assessments. English edition with updated taxonomy and added species[END_REF].

Gomphosphenia lingulatiformis might occur quite common in alkaline, eutrophic to eupolytrophic rivers, canals, and lakes [START_REF] Krammer | Bacillariophyceae 1 Teil: Naviculaceae. In: Süßwasserflora von Mitteleuropa[END_REF][START_REF] Lange-Bertalot | Freshwater benthic diatoms of Central Europe: over 800 common species used in ecological assessments. English edition with updated taxonomy and added species[END_REF].

Nowadays new species are still observed and described such as G. plenkoviciae Gligora Udovič & Zutinić in Gligora Udovič et al. (2018: 231) in a karstic sinkhole lake and G. patrickiana Cantonati, Lange-Bertalot, Kociolek & A.A.Saber in Saber et al. (2021: 222) in rivers from Puerto Rico. According to AlgaeBase (Guiry & Guiry 2021) and DiatomBase [START_REF] Kociolek | DiatomBase[END_REF], the genus Gomphosphenia holds 18 species and 3 varieties (Annex).

In the Massif Central different surveys on diatoms are regularly conducted, and new species are observed and described [START_REF] Beauger | Two new Navicula species (Bacillariophyceae) from Western Europe[END_REF][START_REF] Beauger | Sellaphora labernardierei (Sellaphoraceae, Bacillariophyta), a new epilithic species from French spring and four new combinations within the genus Sellaphora[END_REF][START_REF] Beauger | Morphology and ecology of Craticula lecohui sp. nov. (Bacillariophyceae) from hydrothermal springs (Puy-de-Dôme, Massif Central, France) and comparison with similar Craticula species[END_REF][START_REF] Beauger | Pseudostaurosira bardii (Fragilariaceae, Bacillariophyta), a new species from a saline hydrothermal spring of the Massif Central (France)[END_REF]. In summer 2021, during a study on the diatom biodiversity of the "Réserve Naturelle Nationale de la Vallée de Chaudefour" (RNN VC), different samples were taken in headwater and mineral springs. A small-sized Gomphosphenia was observed in the Pérouse Stream. Following detailed light microscopy (LM) and scanning electron microscopy (SEM) observations and comparisons with known representatives of this genus, this Gomphosphenia is described as new. A morphological comparison is made with the most similar Gomphosphenia taxa. Moreover, ecological information about the new species is also provided.

Material & Methods

Study site:-The Pérouse Stream is located in the French Massif Central region, in the department of Puy-de-Dôme (63) and more precisely in the Chaudefour Valley (Fig. 1).

Nowadays this valley is protected with the establishment of the RNN VC that covers 820.50 hectares. Located in the heart of the Monts Dore, on the Sancy massif, which highest point is at an elevation of 1,886 m high (Réserves naturelles de France 2021; Rossi 2021). This valley appeared around 600,000 years ago and was created by the partial destruction of the Sancy's volcanic massif [START_REF] Lavina | Carte volcanologique de la Réserve Naturelle de la vallée de Chaudefour, Strato-volcan du Sancy, Massif des Monts Dore, Massif Central Français[END_REF]. The lateral collapse of the volcano was caused by a violent eruption. This explosion created a glacial cirque where about thirty volcanoes appeared that constitute the current structure of the ridges [START_REF] Lavina | Carte volcanologique de la Réserve Naturelle de la vallée de Chaudefour, Strato-volcan du Sancy, Massif des Monts Dore, Massif Central Français[END_REF][START_REF] Audubert | La Commission de volcanisme dans les monts Dore (2 e )[END_REF] Réserves naturelles de France 2021). The typical shape of the valley is caused to glacial erosion. Lava needles and dykes (such as the "dent de la Rancune") have appeared as a result of fluvio-torrential erosion.

A multitude of headwater streams, among them Pérouse Stream, coming from the glacial valley confluence to form the river called "Couze de Chaudefour". The Pérouse Stream has its source in the upper part of the valley, in subalpine bogs of the reserve. It flows into the valley at the "Cascade de Pérouse" that is present at the entrance of the cirque. The sampling point was taken at the coordinates 2°51'11"E, 45°32'12"N and at 1,184 meters a.s.l.

Diatom sampling and physical and chemical analysis:-Five stones were removed from a riffle to make a composite epilithic sample. While in the field, the stones were brushed using a toothbrooth on 20 th August 2021. The sample was fixed with an ethanol solution to a final concentration of 70%. In-situ, pH (pH unit), conductivity (μS.cm -1 ) and water temperature (°C) were measured at the sampling site using a WTW Multiline P4. For Dissolved oxygen (% and mg L -1 ), a ProODO oxygen probe was used. A water sample was collected for further chemical analysis in the laboratory This sample was first filtered using Whatmann GF/C filters. Then, it was analyzed with the high-pressure ion chromatography technic to obtain ionic concentrations of lithium, sodium, ammonium, potassium, magnesium, calcium, bromine, fluoride, chloride, nitrite, nitrate, phosphate and sulphate (in mg L -1 ). For the cations analysis a Thermo Scientific Dionex ICS1100 system was used, while for the anions a Thermo Scientific Dionex Aquion system was used. .

Slide preparation and microscopy:

-Two milliliters of preserved material were prepared for LM observation following the method described in [START_REF] Prygiel | Guide méthodologique pour la mise en oeuvre de l'indice Biologique Diatomées NF T 90-354[END_REF]: cleaning using H2O2 and dilute hydrochloric acid. After several rinses in distilled water, a portion of the cleaned diatom material was air-dried onto a cover slips and then mounted in Naphrax®. LM observations were done using a Leica® DM2700M microscope with 100x oil immersion objective using a differential interference contrast.

The species present were identified according to different taxonomical works [START_REF] Krammer | The genus Pinnularia[END_REF], 2002[START_REF] Krammer | Cymbopleura, Delicata, Navicymbula, Gomphocymbellopsis, Afrocymbella[END_REF][START_REF] Lange-Bertalot | 85 neue Taxa und über 100 weitere neu definierte Taxa ergänzend zur Süßwasserflora von Mitteleuropa, Vol. 2/1-4. 85 New Taxa and much more than 100 taxonomic clarifications supplementary to Süßwasserflora von Mitteleuropa Vol. 2/ 1-4[END_REF][START_REF] Lange-Bertalot | Oligotrophie-Indikatoren. 800 Taxa repräsentativ für drei diverse Seen-Typen. Kalkreich -Oligodystroph -Schwach gepuffertes Weichwasser [Indicators of oligotrophy. 800 taxa representative of three ecologically distinct lake types. Carbonate buffered -Oligodystrophic -Weakly buffered soft water[END_REF][START_REF] Wetzel | Morphology, typification and critical analysis of some ecologically important small naviculoid species (Bacillariophyta)[END_REF][START_REF] Levkov | The diatom genus Gomphonema from the Republic of Macedonia[END_REF][START_REF] Lange-Bertalot | Freshwater benthic diatoms of Central Europe: over 800 common species used in ecological assessments. English edition with updated taxonomy and added species[END_REF] and the count data were converted into percentage relative abundance in respect to the total count (424 valves) for each sample.

Morphometric measurements were performed using a Leica® DMRX brightfield microscope with 100x oil immersion objective, and light micrographs were taken with a Leica® DMC 2900 camera.

For scanning electron microscopy (SEM), parts of the oxidized suspensions were filtered with additional deionized water through a 0.2 µm Isopore polycarbonate membrane filter (Merck Millipore). Filters were mounted on aluminum stubs and coated with carbon. An ultrahighresolution analytical field emission (FE) scanning electron microscope, Hitachi Regulus 8230 (Hitachi High-Technologies Corporation, Japan), was operated at 2 kV and 10 mm distance for image analysis.

Images were digitally manipulated and plates containing light and scanning electron microscopy micrographs were created using Adobe InDesign 16.4. Samples and slides are stored at the Herbiers Universitaires de Clermont-Ferrand (France) and Botanic Garden Meise (Belgium). Diatom terminology follows [START_REF] Ross | An amended terminology for the siliceous components of the diatom cell[END_REF], [START_REF] Barber | A guide to the morphology of the diatom frustule with a key to the British freshwater genera[END_REF] (valve shape, stria/areola structure) and [START_REF] Round | The diatoms: biology & morphology of the genera[END_REF] (raphe characteristics). Striae slightly radiate in central part of valve, becoming convergent towards both head and footpoles. Raphe straight, filiform, with slightly dilated distal and proximal raphe endings . Distal raphe fissures terminating on the valve face, not extending onto the valve mantle (Fig. 28). Internally, proximal raphe endings bent in the same direction (Fig. 31).

Results

Detailed morphological description of

Internal terminal raphe fissures ending in helictoglossae (Fig. 31). Single row of slit-like areolae located on the valve mantle (Figs 26,28,30,32), sometimes rounded in shape near the mid-valve and towards the footpole (Figs 27,33). Central area with a unilateral fascia, with a short areola on one side and absence of areola on the other side . Central nodule slightly raised (Fig. 31). Apical pore fields absent (Fig. 28). In girdle view, frustules with cingulum composed of open bands, each bearing one row of small round pores (Figs 28,30,(32)(33).

Discussion

The "Réserve Naturelle Nationale de la Vallée de Chaudefour" is a glacial valley which shelters a great diversity of protected species of flora and fauna, typical of the Alps and of great scenic and scientific interest. To complete the knowledge on the reserve, a diatom survey done in summer 2021 has highlighted the presence of a new species of Gomphosphenia.

Among the 18 Gomphosphenia species, G. vallei present similarities with only four Gomphosphenia species (Table 1) (1995: 243), 3) broadly lanceolate-clavate with protracted rostrate head and footpoles such as G. praegnans Ress, E.W. Thomas & Kociolek (2016: 56, 57), 4) linear lanceolate outline such as G. oahuensis (Hustedt 1942a: 98) Lange-Bertalot in Moser et al. (1998: 42).

The striae was another characteristic to separate the new species from other ones. Indeed, G. grovei, G. pfannkucheae (Cholnoky 1966: 25, 26) Lange-Bertalot (1995: 244), G. reicheltii (M.Schmidt 1899: 214) Lange-Bertalot (1995: 244), G. ryukyuensis, G. tackei (Hustedt 1942b: 205) Lange-Bertalot (1995: 244) and G. tenerrima (Hustedt 1938: 444) E. Reichardt (1999: 57) are characterized by striae composed of a few areolae, unlike to the new species that are composed of a single long radiate slit-like areolae. Moreover, the internal proximal raphe endings of the new species are not T-shaped such as the generitype G. lingulatiformis and also G. biwaensis, G. holmquistii [START_REF] Foged | Some new or rare diatoms from Alaska[END_REF]: 8) Lange-Bertalot (1995: 244), G. plenkoviciae, G. patrickiana, G. ryukyuensis, G. tackei and G. tenuis Levkov & D.M.Williams (2011: 20) but they are deflected in the same direction.

Thus, only the four species, previously named, can be compared to the new species.

Gomphosphenia americana has valves lanceolate-clavate [START_REF] Kociolek | Diatoms of the United States, 1 Taxonomy, ultrastructure and descriptions of new species and other rarely reported taxa from lake sediments in the western U.S.A[END_REF]. The number of striae is higher than the new species with 29 to 32 striae in 10 µm. Moreover, in girdle view, valves are cuneate and flexed about the transapical axis differing in this pattern from the new species. When considering G. fontinalis, the outline is clavate while G. vallei is linear-clavate (and clavate to elliptical for smaller individuals). The valve dimensions are comparable to the new species (Werum & Lange-Bertalot 2004). However, less striae are observed in the new species (23-29 in 10 µm). Indeed G. fontinalis has 25 to 32 striae in 10 µm for Werum & Lange-Bertalot (2004) and, 32 to 36 striae in 10 µm according to the observations of [START_REF] Noga | The inside of a dam as an unusual habitat for two rare species of Gomphosphenia -G. fontinalis and G. holmquistii[END_REF].

The new species is longer (4.2 to 13.1 µm) compared to G. fontinalis (5.0-8.0 µm for Werum & Lange-Bertalot 2004 and 3.2-7.9 µm for [START_REF] Noga | The inside of a dam as an unusual habitat for two rare species of Gomphosphenia -G. fontinalis and G. holmquistii[END_REF]. Moreover for G. fontinalis, transapical striae are very short and subparallel in marginal position (Werum & Lange-Bertalot 2004). Striae of G. fontinalis can be longer in some individuals related to the observations of [START_REF] Noga | The inside of a dam as an unusual habitat for two rare species of Gomphosphenia -G. fontinalis and G. holmquistii[END_REF] while for G. vallei the striae are longer, composed of single slit-like areolae.

Gomphosphenia fontinalis is characterized by a wide central area, not distinctly separated from the axial area. For G. vallei, the central area is absent to asymmetrical and appeared as a unilateral fascia in SEM, with a short areola on one side and absence of areola on the other side, and the axial area is linear and narrow. Internally, the proximal raphe endings are deflected in the same direction for G. vallei while they "declined unilaterally as small hooks" in G.

fontinalis. At last, in girdle view, the frustules of G. vallei are almost rectangular to slightly wedge-shaped while for G. fontinalis they are club-shaped.

Gomphosphenia indistincta present valves linear-lanceolate clavate with margins with undulations in larger specimens [START_REF] Kociolek | Diatoms of the United States, 1 Taxonomy, ultrastructure and descriptions of new species and other rarely reported taxa from lake sediments in the western U.S.A[END_REF], a pattern never observed in G. vallei. This species is longer (7.5-25 µm) and larger (2-3 µm) than the new species. At last, G. stoermeri present valves linear-clavate with rounded to narrowly rounded poles. This species is longer (10-21.1 µm) and the density of striae is higher (28-35 striae in 10 µm) (Thomas et al. 2009) than for G. valley (length: 4.2-13.1 µm; number of striae: 24-29 in 10 µm).

Moreover internal proximal raphe endings are tightly hooked in one direction while for G. vallei they are deflected in one direction. In girdle view, frustules are slightly wedge-shaped for both species.

Furthermore, the other comparable species have a different ecology (Table 2). Indeed, G. vallei was collected in a headwater stream in running waters of low conductivity in a granitic and volcanic context while G. americana and G. indistincta were found in lakes (Kociolek et al. 2014). For G. fontinalis, this species is apparently typical of carbonate springs (Werum & Lange-Bertalot 2004[START_REF] Straub | Biodiversité en Ville de Neuchâtel : Diatomées et autres organismes microscopiques[END_REF][START_REF] Noga | The inside of a dam as an unusual habitat for two rare species of Gomphosphenia -G. fontinalis and G. holmquistii[END_REF][START_REF] Peeters | Quelques diatomées des sources du territoire bourguignon[END_REF]. At last, G. stoermeri was observed as epilithic, subaerial in Cataract Falls [START_REF] Thomas | Taxonomy, ultrastructure and distribution of gomphonemoid diatoms (Bacillariophyceae) from Great Smoky Mountains National Park (U.S.A.)[END_REF]) and also in rivers in northern Sweden ( [START_REF] Van De Vijver | New and interesting diatom species (Bacillariophyceae) from Swedish rivers[END_REF].

In conclusion, this study of the diatom community done in the "Réserve Naturelle Nationale de la Vallée de Chaudefour" revealed a small-sized species of Gomphosphenia with a previously unknown combination of the morphological characteristics (shape, size, internal proximal raphe endings) leading to the description of G. vallei. This species was observed in a small stream of the reserve. Additional investigations are needed to identify other sites with the presence of this species.

  Gomphosphenia vallei Beauger, C.E.Wetzel, Allain & Ector sp. nov. (Figs 2-45, Tab. 2) are presented in this paper from the sample taken in Pérouse Stream. Class: Bacillariophyceae Haeckel emend. Medlin & Kaczmarska 2004: 267 Subclass: Bacillariophycidae D.G.Mann in Round et al. 1990: 128 Order: Cymbellales D.G.Mann in Round et al. 1990: 128 Family: Rhoicospheniaceae J.Y.Chen & H.Z.Zhu 1983: 453 Genus: Gomphosphenia Lange-Bertalot 1995: 243 Gomphosphenia vallei Beauger, C.E.Wetzel, Allain & Ector sp. nov. (Figs 2-45) Light microscopy observations (Figs 2-25): Valves linear-clavate in larger specimens to clavate in smaller ones and elliptical in the smallest individuals. Headpoles rounded, footpoles narrowly rounded. Valve dimensions (n = 30): length 4.2-13.1 μm, width 1.5-2.5 μm. Raphe straight, filiform. Striae visible in LM, almost parallel throughout the valve to slightly radiate in the mid-valve, 23-29 in 10 μm. Axial area linear and narrow. Central area from absent to asymmetrical with round and distinct central nodule. In girdle view, frustules almost rectangular to slightly wedge-shaped. Scanning electron microscopy observations (Figs 26-33): Valve face flat. Externally, striae composed of single slit-like areolae, becoming very short slit near the poles (Figs 26-30).

  abbreviata (C.Agardh 1831: 34) Lange-Bertalot (1980: 586) (30%). The other species well represented (<10%) were Achnanthidium subatomus(Hustedt 1939: 554) Lange-Bertalot (1999: 273) (7.1%), Gomphonema sp. cf. minutum C.Agardh (1831: 34) (6.4%), Navicula reichardtiana Lange-Bertalot in Lange-Bertalot & Krammer (1989: 163) (2.3%), Odontidium mesodon (Ehrenberg 1839: 57) Kützing (1849: 12) (2.3%), Gomphosphenia vallei (2.3%), Reimeria sinuata (W.Gregory 1856: 4) Kociolek & Stoermer (1987: 457) (1.9%), Planothidium curtistriatum C.E.Wetzel, Van de Vijver & Ector in Wetzel et al. (2019: 61) (1.9%), Cocconeis rouxii Héribaud & Brun in Héribaud (1893: 45) (1.9%) and Encyonema minutum (Hilse inRabenhorst 1862: No. 1261) D.G.Mann in Round et al. (1990: 667) (1.1%). At last, Chamaepinnularia obsoleta (Hustedt 1942a: 69) C.E.Wetzel & Ector in Wetzel et al. (2013: 158), Cyclotella antiqua W.Smith (1853: 28), Geissleria acceptata (Hustedt 1950: 398) Lange-Bertalot & Metzeltin (1996: 64), Gomphonema clavatum Ehrenberg (1832: 88), Gomphonema exilissimum (Grunow in Van Heurck 1880: pl. 25, fig. 12) Lange-Bertalot & E.Reichardt in Lange-Bertalot & Metzeltin (1996: 70), Humidophila perpusilla (Grunow 1860: 552) R.L.Lowe, Kociolek, J.R.Johansen, Van de Vijver, Lange-Bertalot & Kopalová (2014: 358),Mayamaea permitis[START_REF] Hustedt | Diatomeen aus Seen und Quellgebieten der Balkan-Halbinsel[END_REF]: 919) Bruder & Medlin (2008: 327), Meridion constrictumRalfs (1843: 458), Nitzschia hantzschianaRabenhorst (1860: 40), Nitzschia soratensis E.Morales & M.L.Vis (2007: 128), Nupela lapidosa(Krasske 1929: 350) Lange-Bertalot (1999: 274), Pantocsekiella ocellata(Pantocsek 1901: 134) K.T.Kiss & Ács inÁcs et al. (2016: 62), Pinnularia sinistraKrammer (1992: 105), Psammothidium helveticum(Hustedt 1933: 385) Bukhtiyarova& Round (1996: 8), Psammothidium subatomoides(Hustedt in Schmidt et al. 1936: pl. 404)Bukhtiyarova & Round (1996: 13) and Sellaphora atomoides(Grunow in Van Heurck 1880: 107) C.E.Wetzel & Van de Vijver in Wetzel et al. (2015: 219) represented less than 1% of the whole community.

  : G. americana Kociolek & E.W.Thomas in Kociolek et al. (2014: 45), G. fontinalis Lange-Bertalot, Ector & Werum in Werum & Lange-Bertalot (2004: 163), G. indistincta Kociolek & E.W.Thomas in Kociolek et al. (2014: 46) and G. stoermeri Kociolek & E.W.Thomas in Thomas et al. (2009: 230). Indeed, the shape of G. vallei (linear-clavate to elliptical for the smallest individuals) allowed to separate it from species presenting: 1) clavate outline with broadly rounded headpole such as G. ryukyuensis Tuji & Ohtsuka in Tuji (2016: 2), 2) linear-clavate with headpole obtusely cuneate, gradually tapered from the central portion to the footpole such as G. biwaensis Ohtsuka & D.Nakai in Ohtsuka et al. (2018: 108) and G. grovei (M.Schmidt 1899: 214) Lange-Bertalot

FIGURE 1 .

 1 FIGURE 1. Map of the studied stream. a: map of Europe; b: map of France; c: location of the sampling site (star); d: photograph of the sampling site in the Chaudefour Valley taken from the upper part of the cirque; e: photograph of the sampling site in the Chaudefour Valley taken from the access road to the Reserve; f: photograph of the Pérouse Stream taken in July 2021.

FIGURES 26 -

 26 FIGURES 26-33. SEM images of Gomphosphenia vallei. Type population from Pérouse Stream. 26-30: External view of entire valve showing the raphe structure and the striae. 31: Internal view of an entire valve showing the raphe structure and the striae: 32-33: Girdle view of the frustule. Scale bar = 5 μm (Figs 29-31), 4 μm (Figs 27, 32), 3 μm (Figs 26, 33) and 2 μm (Fig. 28).

TABLE 1 .

 1 Physical and chemical variables measured in the spring (below detection limit:

	Bdl).
		Pérouse
		Stream
	Conductivity (µS cm -1 )	35
	pH (pH units)	7.09
	Temperature (°C)	11.90
	Dissolved oxygen (%)	92.90
	Li + (mg L -1 )	Bdl
	Na + (mg L -1 )	2.53
	NH4 + (mg L -1 )	Bdl
	K + (mg L -1 )	1.93
	Mg 2+ (mg L -1 )	0.84
	Ca 2+ (mg L -1 )	2.38
	F -(mg L -1 )	0.05
	Cl -(mg L -1 )	1.04
	NO3 -(mg L -1 )	0.57
	NO2 -(mg L -1 )	0.01
	Br -(mg L -1 )	Bdl
	PO4 3-(mg L -1 )	0.11
	HCO 3-(mg L -1 )	16.50
	SO4 2-(mg L -1 )	0.67

TABLE 2 .

 2 Main characteristics of Gomphosphenia vallei and 4 similar Gomphosphenia species.

	Species	Valve length (µm)	Valve width (µm)	Number µm) of striae (in 10	Valve outline	Areolae	Axial area	Central area	Internal endings proximal raphe	Girdle view	Ecology
					linear-clavate	striae uniseriate,
	Gomphosphenia vallei	4.2-13.1	1.5-2.5	23-29	in larger specimens to clavate in smaller ones and elliptical in the smallest	composed of single slit-like areolae, becoming almost round poroids near the	linear and narrow	absent to asymmetrical	deflected in one direction	almost rectangular to slightly wedge-shaped	in running waters (streams) with low conductivity
					individuals	poles
	Gomphosphenia americana Kociolek & E.W.Thomas in Kociolek et al. (2014: 45)	9.0-13.0	2.0-3.0	29-32	lanceolate-clavate	single elongated areola	linear and narrow	linear to circular, sometimes asymmetrical	recurved to one side	cuneate and axis flexed about transapical the	in lakes
	Gomphosphenia										species of
	fontinalis Lange-Bertalot, Ector & Werum in Werum & Lange-Bertalot	5.0-8.0	1.5-2.3	25-32(36)	club-shaped	single elongated areola	lanceolate	wide, not distinctly separated from the axial area	unilaterally deflected as small hooks	wedge-shaped	carbonate water, apparently strictly dependent on
	(2004: 163)										karstic springs
	Gomphosphenia indistincta Kociolek & E.W.Thomas in (2014: 46) Kociolek et al.	7.5-25.0	2.0-3.0	almost 24	linear-lanceolate specimens in larger clavate with margins with undulations	single elongated areola	narrow straight	asymmetrical-expanded	recurved in one direction	/	in lakes
	Gomphosphenia										epilithic,
	stoermeri Kociolek & E.W.Thomas in Thomas et al.	10.0-21.1	1.5-3.1	28-35	linear-clavate	single elongated areola	rather narrow, linear	absent to only weakly developed	tightly hooked in one direction	slightly wedge-shaped	subaerial in Cataract Falls, on rivers of northern
	(2009: 230)										Sweden

Acknowledgements

Funding for this research was partly provided by funded by the Direction Régionale de l'Environnement, de l'Aménagement et du Logement Auvergne-Rhône-Alpes, and by the "Réserve Naturelle Nationale de la Vallée de Chaudefour" and in the framework of the DIATOMS project (LIST-Luxembourg Institute of Science and Technology). Anonymous reviewers are thanked for their valuable comments.