Navicula flandriae Van de Vijver & A.Mertens, 2015

Beauger, Aude, Voldoire, Olivier, Mertens, Adrienne, Cohu, René Le & Vijver, Bart Van De, 2015, Two new Navicula species (Bacillariophyceae) from Western Europe, Phytotaxa 230 (2), pp. 172-182 : 175-177

Navicula flandriae Van de Vijver & A.Mertens , sp. nov. ( Figs 41–65 )

LM ( Figs 41–61 ): Valves narrowly lanceolate to weakly elliptic-lanceolate in smaller specimens. Valve margins linear to slightly convex, gradually narrowing towards the non-protracted, acutely rounded to wedge-shaped apices. Valve dimensions (n=25): length 35–65 μm, width 7.0–9.5 μm. Axial area very narrow, linear, weakly widening near the central area. Central area small, rounded to almost rectangular, usually slightly asymmetric, bordered by several more distantly spaced, irregularly shortened striae. Raphe filiform with almost straight, clearly expanded proximal raphe endings. Striae radiate and geniculate near the valve center, becoming rapidly parallel and even convergent near the apices, 12–13 in 10 μm. Voigt discordance clearly visible. Lineolae weakly discernible, ca. 32 in 10 μm. SEM ( Figs 62–65 ): Proximal raphe endings almost straight to slightly undulating terminating in clearly expanded, droplike pores ( Figs 62, 64 ). Distal raphe fissures clearly hooked to the secondary side ( Fig. 63 ). Striae composed of lineolae as long as the width of the virgae, 30–34 in 10 μm, clearly longer than the virgae near the apices ( Fig. 63 ). External raphe sternum not raised ( Fig. 62 ). Internally, raphe running weakly lateral of the raphe sternum with the raphe slit opening on the side, but with central raphe endings in the middle of the central area ( Fig. 65 ). Areolae covered by individual hymenes ( Fig. 65 ).

Type: — BELGIUM. Stenenschuurbrug: Leopoldkanaal, sample VMM70-2010 (51° 15’ 59.24” N, 03° 39’ 39.09” E), Vlaamse Milieu Maatschappij, 28 June 2010 (holotype: BR! slide no. 4428; isotype: PLP! slide no. 291, University of Antwerp , Belgium) .

Etymology: — The species is named after Flanders ( Flandria ), the northern region in Belgium where the new species was observed in several rivers (Leopoldkanaal, Oostpolderkreek).

Ecology and Distribution: — Navicula flandriae was observed in several canals and rivers in Flanders, the region occupying the northern part of Belgium. The largest population was found in the Leopoldkanaal presenting an alkaline pH (8.7), high conductivity (7270 μS cm-1) and chloride (1750 mg l-1) levels and moderate nutrient levels (nitrate: 4 mg l-1). Accompanying taxa include Nitzschia liebetruthii Rabenhorst (1864: 157) , Rhoicosphenia abbreviata (C. Agardh 1831: 34) Lange-Bertalot (1980b: 586) , Tabularia fasciculata (C. Agardh 1812: 35) D.M. Williams & Round (1986: 326) and Cyclotella meneghiniana Kützing (1844: 50) . The species has recently been observed in several other rives and canals along the Belgian coast (Van de Vijver, unpublished results).

Figures

FIGURES 41–61. Navicula flandriae Van de Vijver & A.Mertens, sp. nov., LM. Type population from Leopoldkanaal. Scale bar = 10 μm.

FIGURES 62–65. Navicula flandriae Van de Vijver &A.Mertens, sp. nov., SEM.Type population from Leopoldkanaal. 62. External view of an entire valve showing the raphe structure and the striae. 63. External detail of the apex with the typical hooked distal raphe ending. 64. External detail of the central area. Note the typical weakly deflected proximal raphe endings. 65. Internal detail of the central area showing the typical areola coverings, the proximal raphe endings and the laterally running raphe branches. Scale bar = 10 μm (Figs 62, 63), 5 μm (Figs 64, 65).