Anorthoneis dulcis Hein 1991: 269

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 : 212-213

Anorthoneis dulcis Hein 1991: 269 ( Figs 14–34 )

References:— Hein (1991), p. 269, figs 2–21, 25–28; Tremarin & Ludwig (2008), figs 1–9, 10–24; Garcia & Talgatti (2008), figs 3–9; López Fuerte et al. (2011), figs 2–5.

Description. Valves broadly elliptical to ovoid in outline ( Figs 23 , 28 ). Apical axis: 14–16 μm, transapical axis: 9.2–12 μm. SV:— Externally, valve face flat to concave, becoming convex in the undifferentiated mantle, terminating in small marginal area ( Figs 23, 24 ). Eccentric sternum neither raised nor thickened. The central area is asymmetric and larger on the wider hemivalve ( Fig.23 ). Uniseriate transapical striae (22 in 10 μm) composed of circular areolae (20 in 10 μm) internally occluded by slightly perforated hymenes, in both the valve face and the mantle ( Figs 25, 26 ). Close to the valve margin, each stria terminates with one larger, apically elongated or irregular areola ( Fig. 26 ). Internally, the valve structures appear largely similar to the external ones, except for the sternum and the central area, which are visibly thicker ( Figs 25, 27 ). RSV:— Externally, valve face flat to convex, curving gradually to form a wide, concave mantle terminating in hyaline marginal area ( Fig. 32 ). Raphe-sternum eccentric, developed entirely within the valve face. Straight, expanded, pore-like proximal raphe endings ( Fig. 29 ) converge coaxially on the asymmetric, subtriangular, in its wider part, and semi-circular, in its narrower part, central area ( Fig. 28 ). Distal raphe endings similar in shape to the proximal ones terminate in roundish submarginal areas, close to the valve face-mantle junction ( Fig. 30 ). Uniseriate valve face striae (18 in 10 μm) separated from the mantle striae by faint, hyaline, submarginal area present on the valve face-mantle junction ( Fig. 28 , arrow). Mantle striae uniseriate, becoming biseriate towards the valve margin ( Figs 28, 30 ). Areolae (20 in 10 μm) small, circular, occluded by hymenes ultrastructurally similar to those in the SV. Close to the valve margin, in correspondence of each biseriate stria, a larger, apically elongated areola is present ( Figs 28, 30 ). Internally, raphe-sternum, central nodule, and submarginal hyaline area clearly thickened and raised ( Figs 33 and 34 ). Proximal raphe endings hooked, deflected in opposite directions, converging on the central nodule ( Fig. 31 ). Distal raphe endings terminating in vestigial helictoglossae, hardly reaching the hyaline terminal areas ( Fig. 32 ).

Figures

FIGURES 14–22. Anorthoneis dulcis specimens from Hein (1991). (14) Raphe-sternum valve LM micrograph of A. dulcis from Hein (1991), fig. 2 (holotype); (15) Raphe-sternum valve LM micrograph of A. dulcis from Hein (1991), fig. 3; (16) Sternum valve LM micrograph of A. dulcis from Hein 1991, fig. 3’; (17) Sternum valve LM micrograph of A. dulcis from Hein (1991), fig. 2’ (holotype); (18, 19) LM micrographs of A. dulcis sternum and raphe-sternum valve from holotype (slide ANSP A-GC #55788, Diatom herbarium, Philadelphia Academy of Natural Sciences); (20–22) LM micrographs of A. dulcis sternum and raphe-sternum valves from holotype (slide ANSP A-GC #55788, Diatom herbarium, Philadelphia Academy of Natural Sciences). Scale bars: Figs 14, 17–19 = 10 μm; Figs 15, 16, 20–22 = 5 μm.

FIGURES 23–27. Anorthoneis dulcis specimens from Hein (1991), original material #4138, Withlacoochee River, Fla, U.S.A, ANSP Material Collection, Philadelphia Academy of Natural Sciences, SEM images. (23) External view of sternum valve showing asymmetrical subtriangular central area; (24) Tilted external view (60°) of sternum valve showing the convex external mantle; (25) Internal view of sternum valve; (26) Detail of mantle showing the apically elongated areolae at the end of each stria; (27) Tilted internal view (60°) of sternum valve showing the slight thickening of sternum and central area. Scale bars: Figs 23–24, 29 = 5 μm; Fig. 25 = 2 μm; Fig. 26 = 1 μm.

FIGURES 28–34. Anorthoneis dulcis specimens from Hein (1991), original material #4138, Withlacoochee River, Fla, U.S.A, ANSP Material Collection, Philadelphia Academy of Natural Sciences, SEM images. (28) External raphe-sternum valve with faint, hyaline, submarginal areas (arrow);(29) External coaxial, expanded, pore-like proximalraphe endings; (30) External distal raphe ending terminating in a roundish submarginal hyaline area; (31) Proximal raphe endings hooked in opposite directions and to the central nodule; (32) Internal distal raphe ending terminating in vestigial helictoglossa; (33) Internal view of raphe-sternum valve; (34) Tilted internal view (60°) of raphe-sternum valve showing the thickened raphe-sternum, central nodule and submarginal hyaline area. Scale bars: Figs 28, 33, 34 = 5 μm; Fig. 31 = 2 μm; Figs 29, 30, 32 = 1 μm.