Navicula brachysira Brébisson ex Rabenhorst 1853

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 : 144-145

Navicula brachysira Brébisson ex Rabenhorst 1853 ( Figs 27–41 , 48–52 )

(name replaced by R. Ross in Hartley (1986: 607) by Brachysira brebissonii R.Ross )

LM ( Figs 27–41 ):—Cells solitary. Valves rhombic-lanceolate with weakly rhombic to convex margins and almost non-protracted, acutely rounded apices. Valve dimensions (n=25): length 18.2–27.7 µm, width 4.9–5.8 µm. Axial area narrow, linear. Central area very small, rounded to rhombic. Raphe filiform, straight with simple proximal raphe endings. Distal raphe endings not discernible in LM. Striae lineate, uniseriate, radiate throughout the entire valve, 26– 38 in 10 µm, composed of 3, near the apices 2, in LM clearly discernible areolae. Areolae separated by clear apically running, hyaline lines.

SEM ( Figs 48–52 ):—Valves entirely surrounded by a narrow, elevated ridge, clearly thickened near the valve apices ( Fig. 48 ). Striae uniseriate composed of a series of 3 (near the apices usually 1–2) transapically elongated areolae. Near the central area, striae usually composed of 2 longer areolae. Areolae per stria showing a rather similar length, separated by apically running hyaline undulations on the valve surface ( Fig. 48 ). Areolae foramina with small indentations ( Figs 49, 50 ). Small papillae present on the interstriae, usually 4–6 per interstria, but number rapidly declining towards the apices ( Fig. 49 ). Mantle striae composed of one elongated bacilliform areola ( Fig. 50 ). Near the apices, mantle striae closer together ( Fig. 50 ). Raphe branches bordered by an elevated ridge running from the central area to the apices, never fusing with the marginal ridge ( Figs 48–50 ). Raphe straight with inconspicuous, simple proximal endings ( Fig. 49 ) and short, straight distal endings ( Fig. 50 ). T-shaped raphe endings clearly developed. Internally, central area asymmetrical ( Fig. 51 ) to symmetrical ( Fig. 52 ). Proximal raphe endings unilaterally bent ( Fig. 52 ). Distal raphe endings terminating on weakly raised helictoglossae ( Fig. 51 ). Striae internally covered by continuous, though subdivided hymenes.

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 48–52. Navicula brachysira. All pictures taken from the type population (Falaise). Fig. 48. External view of an entire valve showing the most typical features such as the marginal ridge, the striae always composed of (2)3 areolae, the simple raphe endings and the mantle striae. Fig. 49. Detail view of the central area. Not the presence of the papillae, the regular length of the areolae and the simple proximal raphe endings. Fig. 50. External detail of a valve apex with the typical axial ridge terminating before the marginal ridge, the simple, almost straight distal raphe endings, the T-shaped raphe groove near the apex and the diminishing number of areolae per stria. Fig. 51. Internal view of an entire valve. Fig. 52. Internal detail of the central area with the typical weakly bent proximal raphe endings and the porous hymenate internal coverings of the striae. Scale bar represents 10 µm, except for Figs 49, 50 & 52 where scale bar = 5 µm.