Anorthoneis tenuis Hustedt 1955: 15

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 : 225-227

Anorthoneis tenuis Hustedt 1955: 15 ( Figs 97–111 )

References:— Hustedt (1955), p. 15, pl. 2 fig. 5, pl. 5 figs 14–15; Simonsen (1987), p. 405, pl. 603, figs 15–20.

Description: — Valves elliptic to broadly elliptic ( Figs 104, 109 ). Apical axis: 8.5–14.5 μm, transapical axis: 7.5–9.5 μm.

SV:— Externally, valve face concave to convex close to the short mantle terminating in a hyaline marginal area ( Fig. 103 ). Sternum slightly asymmetrical, narrow, terminating in subcircular terminal areas ( Fig. 103 ). Central area very small ( Fig. 103 ). Transapical striae uniseriate, 18–22 in 10 μm, slightly radiate throughout the whole valve surface. Uniseriate stria composed of small circular areolae (20–22 in 10 μm) internally occluded by hymenes ( Figs 105, 106 ). Close to the valve margin, areolae appear to be smaller and transapically elongated ( Fig. 105 ) Internally, sternum asymmetrical, wide, clearly thickened and raised, expanding centrally into large asymmetrical subcircular central area and distally into roundish to subtriangular terminal areas, distant from the valve margin (104, 107). Other valve structures are similar to the external ones.

RSV:— Valves lightly silicified. Externally. Valve face almost flat, becoming concave close to the very short and shallow mantle ( Figs 109, 110 ). Raphe-sternum apically asymmetric, very narrow, linear, terminating close to the valve face-mantle junction ( Figs 109, 110 ). Central and terminal areas very small, hardly discernible ( Figs 108, 111 ). Striae uniseriate, 30 in 10 μm, becoming biseriate on the mantle ( Figs 109, 111 ). Areolae small, roundish, 35 in 10 μm, occluded by hymenes ultrastructurally similar to those in the SV. The low level of silicification and the small dimensions of areolae give the valve face almost hyaline appearance ( Fig 109 ). Both the central and the distal raphe endings are expanded, pore-like ( Figs 108 , 115 ), the latter terminating somewhat distant from the valve margin ( Fig. 111 ). Valvocopula open, with a smooth inner margin ( Fig. 109 ).

Figures

FIGURES 97–102. Historical reports of Anorthoneis tenuis by different authors. (97) Drawings of sternum and raphe-sternum valves of A. tenuis from Hustedt (1955) (holotype); (98, 99) Micrographs of A. tenuis specimen H65366 from slide ZT2/01, material AM794 from Beaufort, North Carolina, USA (Hustedt Diatom Collection, Bremerhaven, Germany); (100–102) Micrographs of other specimens of A. tenuis from slide ZT2/01, material AM794 from Beaufort, North Carolina, USA (Hustedt Diatom Collection, Bremerhaven, Germany), LM images. Scale bars: Figs 101–106 = 2 μm.

FIGURES 103–111. Anorthoneis tenuis specimens from Hustedt’s cleaned material AM794, Beaufort, North Carolina, USA (Hustedt Diatom Collection, Bremerhaven, Germany), SEM images. (103) Tilted external view (60°) of sternum valve; (104) Sternum valve in internal view; (105) Detail of external sternum valve mantle showing smaller and transapically elongated areola at the end of each stria; (106) Detail of sternum valve mantle in internal view showing irregular areolae; (107) Tilted internal view (60°) of sternum valve; (108) Detail of coaxial, expanded, pore-like raphe central endings in external view; (109) Tilted external view (30°) of raphe-sternum valve with open valvocopula; (110) Tilted external view (60°) of raphe-sternum valve; (111) Detail of the raphe-sternum valve showing the biseriate mantle striae and a expanded, pore-like distal raphe ending. Scale bars: Fig. 107 = 5 μm; Figs 103, 104, 109, 110 = 2 μm; Figs 105, 106, 108, 111 = 1 μm.

FIGURES 112–115. Historical report of Anorthoneis vortex by different authors, LM images. (112–114) A. vortex specimens from Sterrenburg (1987), slide BM 81500, Bergen aan Zee, The Netherlands; (115) A. vortex specimens from Witkowski et al. (2000). Scale bars: Figs 112–114 = 5 μm.