Anorthoneis excentrica (Donkin) Grunow 1867: 10

Pennesi, Chiara, Majewska, Roksana, Sterrenburg, Frithjof A. S., Totti, Cecilia & Stefano, Mario De, 2018, Taxonomic revision and morphological cladistics analysis of the diatom genus Anorthoneis (Cocconeidaceae), with description of Anorthoneis arthus-bertrandii sp. nov., Phytotaxa 336 (3), pp. 201-238 : 208-212

Anorthoneis excentrica (Donkin) Grunow 1867: 10 ( Figs 1–13 )

Basionym:— Cocconeis excentrica Donkin (1858), p. 25 , pl. 3, fig.11.

References:— Grunow (1867), pl. 1, 1a, 2–11; De Toni (1891), p. 468–69; Cleve (1895), p. 166, pl. 3, fig. 12; Peragallo & Peragallo (1897 –1908), p. 24, pl. 5, fig. 1; Boyer (1916), pl. 16, figs 30, 31; Boyer (1927), p. 241; Hustedt (1933), p. 319, fig. 780; Van der

Werff & Huls (1957), pl. 14, fig. 93; Hendey (1964), p. 182, pl. 36, fig. 10; Sterrenburg (1988), p. 363–376, figs 5–6, 24–27, 29; Witkowski et al. (2000), p. 97, pl. 42, fig. 20, pl. 54, figs 9, 10.

Description. Valves broadly elliptical to almost circular in outline ( Figs 1, 3 ). Apical axis: 32–35 μm, transapical axis: 25–28 μm.

SV: — Externally, valve face ( Fig. 10 ) flat, becoming convex towards the undifferentiated, wide mantle, terminating in small marginal area ( Fig. 11 ). Eccentric sternum not well discernible in SEM ( Fig. 10 arrow), not reaching the valve margin, terminating in small, roundish hyaline area ( Fig. 10 arrowhead). Transapical striae uniseriate and radiate on both the valve face and the mantle, 11–12 in 10 μm close to the sternum, becoming denser towards the margin (12–13 in 10 μm), composed of circular areolae (approx. 250 μm, 10–11 in 10 μm) externally occluded by hymenes with short, radial perforations ( Fig. 11 ). In the valve margin, close to the end of each stria, a smaller imperforated areola is present ( Fig. 11 arrows).

RSV: — Externally, valve face flat to convex changing abruptly to concave in the mantle. Asymmetric raphe-sternum developed entirely within the valve face lacks a marked axial area. Proximal raphe endings expanded, pore-like, converge coaxially toward a broad central nodule ( Fig. 12 ). Distal raphe endings similar in shape to the proximal ones, terminating in roundish terminal areas distant from the valve margin ( Fig. 12 ). Radial striae uniseriate, becoming biseriate in the mantle, 10–13 in 10 μm, composed of small circular areolae (12–16 in 10 μm) occluded by hymenes ultrastructurally similar to those in the SV. One smaller areola present at the end of each stria ( Fig. 12 arrows). Internally, both the raphe-sternum and the central nodule thickened and prominent. Distal raphe endings terminating in reduced helictoglossae hardly reaching the hyaline terminal areas ( Fig. 13 ).

Figures

FIGURES 1–9. Historical reports of Anorthoneis excentrica by different Authors. (1) Raphe-sternum valve drawing of A. excentrica from Donkin (1858) (Holotype); (2) Raphe-sternum valve drawing of A. excentrica from Ralfs in Pritchard (1861); (3) Sternum and raphe-sternum valve drawings of A. excentrica from Peragallo & Peragallo (1897–1908); (4) Sternum and raphe-sternum valve drawings of A. excentrica from Hustedt (1933); (5) Sternum valve of A. excentrica from Hendey (1964); (6) Sternum valve of A. excentrica from Sterrenburg (1988); (7) Sternum and raphe-sternum valve of A. excentrica from Witkowski et al. (2000); (8) Sternum valve of A. excentrica from slide BM 1466, Greville collection, LM image; (9) Raphe-sternum valve of A. excentrica from slide BM 1466, Greville collection, LM image. Magnifications: Fig. 6 = x2000; Fig. 7 = x1500. Scale bars: Figs 8, 9 = 10 μm.

FIGURES 10–13. Anorthoneis excentrica from Sterrenburg’s sample 1 (1988), collected from the beach near Bergen aan Zee, Holland (August, 1958), SEM images. (10) External view of sternum valve showing faint eccentric sternum (arrow) and small, roundish terminal areas (arrowhead); (11) Detail of striae with smaller imperforated areola on the valve margin at the end of each stria (arrows); (12) External view of raphe-sternum valve with smaller areola at the end of each stria (arrows). (13) Internal view of raphe-sternum valve. Scale bars: Figs 10, 12, 13 = 10 μm; Fig. 11 = 2 μm.