Sellaphora davoutiana, Heudre & Wetzel & Moreau & Ector, 2018

Heudre, David, Wetzel, Carlos E., Moreau, Laura & Ector, Luc, 2018, Sellaphora davoutiana sp. nov.: a new freshwater diatom species (Sellaphoraceae, Bacillariophyta) in lakes of Northeastern France, Phytotaxa 346 (3), pp. 269-279 : 271-273

Sellaphora davoutiana sp. nov. ( Figs 2–17 )

Light microscopy ( Figs 2–13 ): Valves elliptic-lanceolate with broadly protracted, subcapitate and rounded apices. Length 10.3–13.4 μm (12.4 ± 0.8 μm), width 4.0–4.9 μm (4.4 ± 0.2 μm). Plastid shape unknown. Raphe filiform and straight with distinct central pores. Axial area narrow, linear and slightly widened toward central area. Central area small and elliptical to rectangular with 2 or 3 slightly shortened striae of varying length on either side. Terminal areas with polar bars visible even in LM. Striae radiate, 26–30 (28 ± 1.1) in 10 μm. Areolae not discernible.

Scanning electron microscopy ( Figs 14–17 ): Raised sternum visible. Central pores large and slightly deflected to the primary side, in opposition to the more distinctly deflected terminal fissures. Conopeum absent. Striae uniseriate and slightly sigmoid around the central area. Areolae rectangular to square-shaped in external view, circular and occluded by hymenes in internal view, 60–70 in 10 μm. Areolae of the 3 or 4 striae near the apices often merged. Areolae of the row along the sternum twice as big as the others. Presence of a row of areolae on the mantle, interrupted by terminal fissure of the raphe, with areolae becoming more elongated towards the apices. Girdle bands open and non-porous.

Type:— FRANCE. Grand Est region . La Bresse: Lispach Lake (6° 56’ 35” E 48° 3’ 16” N). Holotype on slide BR4505 , deposited in Botanic Garden Meise (Belgium). Here depicted on Fig. 5 .

Etymology: Dedicated to French General Louis-Nicolas Davout (10 May 1770 – 1 June 1823), Marshal of the Empire, 1st Duke of Auerstaedt and 1st Prince of Eckmühl.

Ecology: The Sellaphora davoutiana ecology is difficult to estimate with certainty, because it has been found in only a few lakes and with very low relative abundances. The following environmental values were measured in early November 2015 on the Lispach Lake (type locality): water temperature 8.5ºC, pH 6.06, conductivity 42 μS. cm-1. The diatom community in the type material showed a high diversity and suggested an oligotrophic, oligosaprobic, weakly mineralized and acidic environment. It was mainly composed by Tabellaria flocculosa (Roth) Kützing , Encyonema neogracile Krammer , Psammothidium helveticum (Hustedt) Bukhtiyarova & Round , P. subatomoides (Hustedt) Bukhtiyarova & Round , Surirella roba L.Leclercq , Navicula notha J.H.Wallace , Frustulia cf. krammeri Lange-Bertalot & Metzeltin , F. amphipleuroides (Grunow) Cleve-Euler , Gomphonema coronatum Ehrenberg , Stauroforma inermis Flower, V.J.Jones & Round , Pinnularia polyonca (Brébisson) W.Smith , and Sellaphora chistiakovae (Kulikovskiy & Lange-Bertalot) C.E.Wetzel, Ector, Van de Vijver, Compère & D.G.Mann. This community also showed a remarkable diversity within the genus Eunotia : E. incisa W.Gregory , E. botuliformis Wild, Nörpel-Schempp & Lange-Bertalot in Lange-Bertalot, E. exigua (Brébisson ex Kützing) Rabenhorst , E. tenella (Grunow in Van Heurck) Hustedt in Schmidt et al., E. faba Ehrenberg , E. meisteri Hustedt , E. microcephala Krasske , E. rhomboidea Hustedt , E. pectinalis (Kützing) Rabenhorst and E. naegelii Migula. Two species belonging to the Coscinodiscophyceae class were found for the first time in the Northeastern France: Aulacoseira laevissima (Grunow) Krammer and A. perglabra (Østrup) E.Y.Haworth.

The diatoms in the phytoplankton of Lispach Lake were studied by Pierre (1983). He underlined a low diversity with dominant species belonging to Eunotia and Pinnularia , but no undetermined Sellaphora species. No studies of phytobenthos samples of this lake were found in the available literature. Sellaphora davoutiana was so far found in two other lakes of the Grand Est region (i.e. Gérardmer Lake and Longemer Lake) with similar physicochemical characteristics, but slightly different diatom species composition (see Heudre et al. 2017 for physicochemical data and species composition from Gérardmer Lake). It could be more widespread, especially in oligo-mesotrophic acidic lakes lying on siliceous bedrock and not restricted to the Vosges Mountains. Further investigation would confirm that this species could also be present in Canada and Spain, and previously identified as “ Navicula sp. 8 ” in Lavoie et al. (2008, p. 118, pl. 27) or as “ Navicula sp. No. 1” in Rivera-Rondón & Catalan (2017, pl. 70, fig. 21).

Figures

FIGURES 2–17. Sellaphora davoutiana (type material from Lispach Lake at La Bresse). Figs 2–13. LM valve views. Holotype depicted on Fig. 5. Scale bar = 10 μm. Figs 14–17. SEM views. 14. Valve in external view. 15. Valve in internal view. 16. Close up on apex showing distal raphe fissure ending in helictoglossae. 17. Valve in external view showing distal raphe ending on the mantle. Scale bars = 2 μm.