Anorthoneis hyalina Hustedt 1955: 15

Anorthoneis hyalina Hustedt 1955: 15 ( Figs 68–87 View FIGURES 68–75 View FIGURES 76–80 View FIGURES 81–87 )

References:— Hustedt (1955), pl. 2 figs 3–4, pl. 5 figs 12–13; Foged (1975), pl. 7, figs 12, 13; Simonsen (1987), p. 404, pl. 604, figs 1–8; Witkowski et al. (2000), p. 98, pl. 51, fig. 1; Garcia & Talgatti (2006), figs 3–4, 9–15.

Description. Valves ovoid to circular in outline ( Figs 76 View FIGURES 76–80 , 81 View FIGURES 81–87 ). Apical axis: 24–36 μm, transapical axis: 20–28μm.

SV:— Externally, valve face flat in its central part, distally convex, curving gradually into a shallow undifferentiated mantle ( Figs 76, 78 View FIGURES 76–80 ). Sternum strongly asymmetric, expanded in the centre, giving rise to a very large, semi-circular central area, occupying more than 2/3 of the entire valve surface ( Figs 76, 78 View FIGURES 76–80 ), covered with randomly scattered, irregular concavities and flanked by groove-like fissures ( Figs 78, 79 View FIGURES 76–80 arrow). Similar irregular, apically elongated groove-like fissures mark the apical axis ( Figs 76, 78 View FIGURES 76–80 ). Striae uniseriate, radiate, 9–11 in 10 μm close to the valve centre, becoming denser towards the margin ( 15–17 in 10 μm), composed of slit-like areolae ( 10 in 10 μm) internally occluded by vela ( Fig. 80 View FIGURES 76–80 ). The internal areola openings are larger than those on the exterior. Internally, almost undiscernible sternum and very large hyaline central area appear heavily silicified and smooth ( Fig. 77 View FIGURES 76–80 ).

RSV:— Externally, valve face concave with slightly raised asymmetrical raphe-sternum ( Figs 81, 84 View FIGURES 81–87 ). Valve mantle wide, terminating at the valve margin in a narrow marginal area bordered by a thickened rim; same thickening occurs on valvocopula ( Figs 82, 85 View FIGURES 81–87 arrows); ligulate structures are visible on the valvocopula ( Fig. 85 View FIGURES 81–87 , black arrow). Striae radiate and strongly radiate near the apices ( Figs 81, 82 View FIGURES 81–87 ), 17–18 in 10 μm, uniseriate, becoming biseriate on the mantle ( Figs 82, 85, 87 View FIGURES 81–87 ). Circular areolae almost equal in size, 30 in 10 μm, occluded by perforated hymenes. A smaller, nonhymenate areola is present on the valve margin, at the end of each stria ( Fig. 85 View FIGURES 81–87 , white arrowhead). Asymmetric central area small, subtriangular ( Figs 81, 83 View FIGURES 81–87 ). Raphe branches straight with close, coaxial, and slightly expanded proximal endings, deflected slightly to one side ( Figs 81, 83 View FIGURES 81–87 ). Distal raphe endings straight, slightly expanded, hardly reaching sub-circular terminal areas, distant from the valve margin ( Fig. 82 View FIGURES 81–87 ). Internally, both the raphe-sternum and the central nodule thickened and prominent ( Fig. 86 View FIGURES 81–87 ). Distal ones end in reduced helictoglossae, not reaching the hyaline terminal areas ( Fig. 86 View FIGURES 81–87 ).