Brachysira sandrae, Vijver, 2014

Vijver, Bart Van De, 2014, Analysis of the type material of Navicula brachysira Brébisson with the description of Brachysira sandrae, a new raphid diatom (Bacillariophyceae) from Iles Kerguelen (TAAF, sub-Antarctica, southern Indian Ocean), Phytotaxa 184 (3), pp. 139-147 : 141-144

Brachysira sandrae sp. nov. ( Figs 2–26, 41–47 )

Type:— KERGUELEN. Val Travers , sample B13, leg. M. Lebouvier, coll. date 31/01/2005 (holotype, slide no. BR –4390; isotype, slide PLP –275, University of Antwerp, Belgium) .

LM ( Figs 2–26 ):—Cells solitary. Valves narrowly lanceolate to rhombic lanceolate with convex margins and clearly protracted, rostrate, rounded apices. Smaller specimens with less protracted though still clearly rostrate apices. Valve dimensions (n=50): length 21–40 µm, width 5.4–7.1 µm.Axial area very narrow, linear. Central area small, symmetrical, rounded to elliptical due to shortened central striae. Raphe straight, filiform with simple, straight proximal endings. Distal raphe endings not visible in LM. Striae lineate, uniseriate, radiate throughout the entire valve, 29–31 in 10 µm, composed of 2–4 in LM clearly discernible areolae.

SEM ( Figs 42–47 ):–Valves entirely surrounded by an elevated ridge, clearly thickened near the valve apices ( Figs 42, 43 ). Striae uniseriate composed of a series of 2–4 (near the apices usually 1) transapically elongated areolae. Areolae per stria showing an irregular length, the outer row usually being the longest, producing apically running hyaline undulations on the valve surface. Areolae foramina with small indentations ( Figs 44, 45 ). Small papillae present on the interstriae, usually 5–7 per interstriae, but number rapidly declining towards the apices ( Fig. 42 ). Mantle striae composed of one elongated bacilliform areola ( Fig. 43 ). Near the apices, mantle striae closer together. Raphe branches bordered by an elevated ridge running from the central area to the apices, never fusing with the marginal ridge ( Figs 44, 45 ). Raphe straight with inconspicuous, simple proximal endings ( Fig. 44 ) and short, straight to weakly deflected distal endings ( Fig. 45 ). T-shaped raphe endings only weakly and irregularly developed. Internally, central area symmetrical ( Fig. 46 ) to asymmetrical ( Fig. 47 ). Proximal raphe endings unilaterally bent ( Fig. 46 ) to straight ( Fig. 47 ). Distal raphe endings terminating on weakly raised helictoglossae. Due to erosion, internal areolar occlusions not observed.

Ecology and Distribution:– Brachysira sandrae was found in several samples collected in some brooks and rivers in the Val Travers area (Kerguelen). The samples were quite species-rich and dominated by Achnanthidium sieminskae Witkowski, Kulikovskiy & Riaux-Gobin (2012: 65) , A. modestiforme (Lange-Bert. in Lange-Bertalot & Krammer 1989: 107) Van de Vijver (in Van de Vijver et al. 2002: 17) and several Psammothidium taxa. The largest population was observed in sample B13, taken from the main hotspring at 70 m altitude with a water temperature of 62.4°C, a pH of 8 and a temperature of 18–20°C in the mosses floating on the surface.

Etymology:—The species is named my dear friend, Mrs Sandra Scheerer (Jena, Germany) in recognition of her efforts in nature conservation and more specifically the protection of native European orchids.

Figures

FIGURES 2–41. LM. Brachysira sandrae (2–26) and Navicula brachysira (27–41). Figs 2–26. Brachysira sandrae, pictures taken from the holotype population (sample B13) from the Val Travers area. Figs 27–41. Navicula brachysira, pictures taken from the type population found in material collected by A. de Brébisson in Falaise and deposited in the Botanic Garden Meise. Scale bar represents 10 µm.

FIGURES 42–47. Brachysira sandrae. All pictures taken from the holotype population (sample B13). Fig. 42. External view of an entire valve showing the most typical features such as the marginal ridge, the striae composed of 2–4 areolae, the simple raphe endings and the mantle striae. Fig. 43. External view of an entire valve in oblique position showing clearly the marginal ridge and the ridge bordering the raphe. Fig. 44. Detail view of the central area. Not the presence of the papillae, the irregular length of the areolae and the simple proximal raphe endings. Fig. 45. External detail of a valve apex with the typical axial ridge terminating before the marginal ridge, the simple, almost straight distal raphe endings and the diminishing number of areolae per stria. Fig. 46. Internal view of an entire valve. Fig. 47. Internal detail of the central area with the typical weakly bent proximal raphe endings. Scale bar represents 10 µm, except for Figs 44 & 47 where scale bar = 5 µm.