Anorthoneis eurystom, Cleve, 1896

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 : 214-215

Anorthoneis eurystom a Clev e 1895: 166 ( Figs35–48 )

References:— Cleve (1895), pl. 3, fig. 12; Boyer (1926–1927), p. 241; Witkowski et al. (2000), p. 97, pl. 54, figs 4–8.

Description. Valves broadly elliptical to circular in outline ( Figs 38, 39 , 42, 43 ). Apical axis: 30–35 μm, transapical axis: 23–28 μm. SV:— Externally, valve face convex, becoming concave along the laterally asymmetric sternum ( Figs 38, 39 ). Sternum short and wide, not well defined, not reaching the valve margin. Central area asymmetric, wide, reaching 1/2 and 1/3 of the hemivalve width ( Fig. 39 ). Valve mantle shallow, undifferentiated, curving abruptly towards hyaline marginal area ( Fig. 40 ). Terminal areas at the sternum apices hardly discernible ( Fig. 39 arrow). Transapical striae uniseriate, slightly radial at the centre and more so towards the apices, 11–13 in 10 μm close to the sternum, 12–14 close to the valve margin. Areolae transapically elongated close to the sternum and more roundish in the vicinity of the valve margin, 10 in 10 μm, Fig. 40 ), occluded internally by vela ( Fig. 40 ). Small, rounded, imperforate areolae present near the central hyaline area ( Fig. 39 ). Internally, the valve structures appear largely, with circular areolae; sternum and hyaline central area appear heavily silicified ( Fig. 41 ).

RSV:— Externally, valve face concave, becoming slightly convex near the asymmetrical axial area ( Figs 42, 44 ). Transapical striae uniseriate radiate on the entire valve, 17–19 in 10 μm, becoming biseriate on the margin. Areolae rounded, 30 in 10 μm, occluded internally by vela ( Figs 43, 46–48 ). At the end of each stria, one smaller areola is present ( Fig. 45 ). Central area irregular, short, expending laterally, with small vestigial pores ( Figs 42, 44 ). Proximal raphe endings expanded, pore-like, close to each other and coaxial ( Fig. 46 ). Distal raphe endings reduced, lying within the hyaline submarginal areas, distant from the valve margin ( Fig. 45 ). Internally, raphe-sternum thickened and prominent ( Fig. 43 ). Proximal raphe endings simple slightly deflected in opposite directions, converging on a central nodule ( Fig. 47 ). Distal raphe endings terminating in reduced helictoglossae ( Fig. 48 ). Valvocopula open, with crenulated inner margin ( Fig. 43 , arrow).

Figures

FIGURES 35–37. Historical reports of Anorthoneis eurystoma by different authors. (35) Sternum valve drawing of A. eurystoma from Cleve (1895) (holotype); (36) Raphe-sternum and sternum valve drawings of A. eurystoma from Hustedt (1955); (37) Sternum and raphesternum valve micrographs of A. eurystoma from Witkowski et al. (2000). Magnification: Fig. 37: x1500.

FIGURES 38–41. Anorthoneis eurystoma specimens from Hustedt cleaned material AM791, Beaufort, North Carolina, USA (Hustedt Diatom Collection, Bremerhaven, Germany), SEM images. (38) External view of sternum and asymmetrical hyaline central area; (39) Tilted external view (60°) of sternum valve showing slightly evident terminal areas close to the mantle (arrow); (40) Detail of sternum valve surface showing the transapically-elongated areole internally occluded by vela; (41) Internal view of sternum valve with strongly silicified sternum and hyaline central area. Scale bars: Figs 39, 41 = 10 μm; Fig. 38 = 5 μm; Fig. 40 = 2 μm.

FIGURES 42–48. Anorthoneis eurystoma specimens from Hustedt cleaned material AM791, Beaufort, North Carolina, USA (Hustedt Diatom Collection, Bremerhaven, Germany), SEM images. (42) Raphe-sternum valve in external view; (43) Raphe-sternum valve in internal view showing the open valvocopula exhibiting a crenulated inner margin (arrows); (44) Tilted external view (60°) of raphesternum valve. (45) External view of a distal raphe ending terminating in a hyaline submarginal area. (46) Detail of expanded, pore-like, coaxial central raphe endings in external view; (47) Internal view of slightly oppositely deflected, central raphe endings converging on a central nodule; (48) Internal view of a distal raphe ending terminating in a reduced helictoglossa. Scale bars: Figs 42–44 = 5 μm; Figs 45–48 = 2 μm.