Eunotia zackenbergensis Goeyers, Van de Vijver & Lange-Bertalot 2022, sp. nov.

Eunotia zackenbergensis Goeyers, Van de Vijver & Lange-Bertalot, sp. nov. (Figs 127–168)

Type:— GREENLAND, Zackenberg (sample M446, coll. date VIII.1998, leg. L. Beyens), holo- BR-4718! (Meise Botanic Garden, Belgium), iso- slide 406! (University of Antwerp, Belgium). The holotype is represented by Fig. 133.

PhycoBank registration:—http://phycobank.org/103148

LM (Figs 127–161): Frustules rectangular in girdle view (Fig. 127). Valves weakly arched with parallel margins. Dorsal margins clearly convex. Ventral margins moderately concave in almost all cell cycle stages, smaller valves becoming more or less straight. Apices protracted, obliquely subcapitate and usually dorsally reflexed in the entire cell diminution series. Valve dimensions (n=50): length 16–62 µm, width 2.5–3.0 µm, length-to-width ratio 6.8–20. Terminal raphe nodules close to the poles. Striae 21–22 in 10 µm, equidistant throughout the entire valve length. Areolae not discernible in LM.

SEM (Figs 162–168): Striae uniseriate throughout, composed of small, rounded areolae, 42–44 in 10 µm (Figs 163, 164). Mantle striae ventrally composed of up to 7 small, rounded areolae near the valve middle (Fig. 162). Apices with two rows of small, circular areolae (Fig. 162). Spines lacking (Figs 162, 163). Externally, raphe branches curving from almost halfway on the valve mantle onto the valve face (Figs 162, 165). Terminal raphe fissures extending ca. halfway towards the dorsal side, visible on the valve face, ending in a distinct pore (Fig. 164). Single rimoportula present at one of both poles, internally located close to the helictoglossa (Figs 166, 167). Helictoglossa prominent at both poles (Figs 167, 168).

Etymology:—The specific epithet zackenbergensis refers to Zackenberg, a Danish research station in the Northeast Greenland National Park in northeastern Greenland, where the species was first identified.

Distribution and ecology:— Eunotia zackenbergensis was collected from very wet mosses, growing in an Arctic bog pond in northeastern Greenland. Van Kerckvoorde et al. (2000) identified the species as E. fallax A.Cleve (Cleve,1895: 33) and grouped the sample (M446) in an assemblage characterised by high frequencies of Rossithidium petersenii (Hustedt) Round & Bukhtiyarova (Hustedt 1937: 179, Round & Bukhtiyarova 1996: 178) and several Pinnularia species. The new species is one of the most frequently observed Eunotia species in Greenland, often reaching relative abundances of up to 70% of the total diatom composition and usually present in bog ponds or fens (Goeyers, unpubl. res.). Due to confusion with E. paludosa, regularly reported from Arctic localities, its precise ecology and distribution is at present not well known.