Brachysira heteropolaris Van de Vijver, 2023

Vijver, Bart Van De, 2023, Brachysira heteropolaris, a new diatom (Brachysiraceae, Bacillariophyta) species observed in an historic Weissflog slide from Scotland (UK), Phytotaxa 587 (1), pp. 47-52 : 48-49

Brachysira heteropolaris Van de Vijver sp. nov. ( Figs 1 –26 LM)

Valves heteropolar, clavate. Valve outline lanceolate with convex margins. Apices not protracted, acutely rounded. At footpole slightly more elongated than at headpole. Valve dimensions (n=40): length 18–35 µm, width 6–8 µm, largest width above the valve middle. Axial area very narrow, linear. Two longitudinal ridges bordering the axial area, running from valve apices to central area. Central area usually small, rounded to elliptical, and raised. Occasionally valves with slightly larger central areas observed (see for instance Figs 7, 11 ). Raphe filiform, raphe branches straight with indistinct, simple central raphe endings. Striae radiate throughout the entire valve length, well discernible in LM, 28–30 in 10 µm. Irregular, short ridges present crossing the striae (e.g. Figs 1, 4, 8 & 14 ).

Type:— UNITED KINGDOM. Loch Canmor 2 (=Loch Kinord), Aberdeenshire 2, Scotland, prep. Weissflog , slide IX-18-A 8 in BR! (holotype slide BR-4777 = Fig. 5 ) .

Registration: —http://phycobank.org/103608

Etymology:—The specific epithet “ heteropolaris ” refers to the heteropolar valve outline.

Ecology & associated diatom flora:—The Weissflog slide was prepared based on material from Loch Canmor. In the Van Heurck collection in BR ( Belgium), several slides from Loch Canmor are conserved, two of them labelled “Loch Canmor 2 – Aberdeenshire – Schottland ” (slides IX-18-A8 &A10). Loch Canmor, nowadays called Loch Kinord is a small, freshwater lake at Muir of Dinnet (Aberdeenshire, Scotland), a few kilometers east of the village of Ballater. This shallow (max. 2m depth) freshwater loch is a part of the Muir of Dinnet National Nature Reserve and an important resting place for wintering birds. The loch is characterised as being oligotrophic and low-alkaline ( Bennion et al. 2004, Lang et al. 2012). The diatom flora in the slide is characterised by a high biodiversity. Dominant species include Brachysira follis , B. brebissonii , B. confusa , Encyonema neogracile Krammer (1997a: 177) , Encyonopsis cesatii var. geitleri Krammer (1997b: 154) , Frustulia saxonica Rabenhorst (1853: 50) , Gomphonema coronatum Ehrenberg (1840: 211) , G. lagerheimii A. Cleve (1895: 22), Tabellaria fenestrata ( Lyngbye 1819: 180) Kützing (1844: 127) , and several Eunotia and Pinnularia species. This species composition reflects dystrophic to oligo-trophic, circumneutral to acidic, oligosaprobic conditions ( Lange-Bertalot & Moser 1994, Lange-Bertalot et al. 2017). Although most species in the slide are acidophilous, several species preferring calcium-carbonate enriched conditions such as Brachysira styriaca , Eucocconeis flexella ( Kützing 1844: 80) F. Meister (1912: 95) , and Navicula radiosa Kützing (1844: 91) are present, though in low abundances. Some of these, such as N. radiosa , could, however, also survive in low-alkaline conditions, though not in high abundances ( Lange-Bertalot 2001).

Figures

FIGURES 1–19. Light micrographs of Brachysira heteropolaris Van de Vijver sp. nov. LM images taken from the holotype population (IX-18-A8, Weissflog slide Loch Canmor, Aberdeenshire 2, Scotland, UK). LM views of the population arranged in decreasing length. Scale bar = 10 µm.