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Scriniodinium dictyotum
Scriniodinium dictyotum Cookson and Eisenack, 1960b, p.248–249, pl.37, figs.8–9.
Holotype: Cookson and Eisenack, 1960b, pl.37, fig.9; Jan du Chêne et al., 1986a, pl.5, fig.1; pl.7, fig.6. Originally (and now) Scriniodinium, subsequently Scriniocassis, thirdly Aldorfia. This species was retained in Scriniodinium by Riding and Fensome (2003, p.16). Age: Oxfordian–Tithonian.
Original description: Cookson and Eisenack, 1960, p. 248
Shell flat, oval, divided by a +/- distinct and relatively broad girdle into an epitheca and hypotheca of approximately equal size; epitheca prolonged into a broadly based, short, blunt apical projection. Capsule oval with a short apical prominence. The wall of the capsule bears numerous thin perpendicular ledges which form a small-meshed supporting reticulum for the thin outer membrane. The meshes of the reticulum vary considerab]y in size and are usually widest towards the periphery. The pylome is broadly hoof-shaped and reaches the girdle.
Dimensions: holotype--109 µm long, 95 µm broad, capsule 95X83 µm.
Supplemental description of North Atlantic Specimens: Habib, 1974, p. 49
Proximate dinoflagellate cysts with polygonal to oval outline. Average W.L.R. 0.90; range from 0.79 to 1.00. Average C. I. 46; range from 45 to 51. Epitract with a short but prominent apical horn that may be open or closed distally; antapical horns lacking. Cingulum narrow, displaced one cingulum width or less. Cyst wall two layered. Periphragm membranous and irregularly reticulate or alveolate, supported by perforate septate sutures. Endophragm oval to polygonal in outline, but always closely approximating outline of cyst. Degree to which the cyst tabulation is expressed varies from almost absent to nearly complete plate formula 4", 0a, 6", 6c, 6""", 1p?, 1""""; plate boundaries incomplete adjacent to sulcus in otherwise well-tabulated specimens; expressed as sutural septa. Archeopyle precingular; formed by the loss of plate 3". Operculum simple and free. Maximum diameter of 45 specimens ranges from 85 to 120 µm; average 105 µm.
Affinities:
Habib, 1974, p. 49-50: The North Atlantic specimens of S. dictyotum differ from S. campanula only in the possession of an alveolate periphragm. They differ from the specimens of S. dictyotum described by Cookson and Eisenack (1960) in the evidence of cyst tabulation. The occurrence of relatively untabulated specimens as well, much like the holotype illustrated by Cookson and Eisenack, indicates that the degree to which the cyst tabulation is expressed varies intraspecifically. In the relatively well-tabulated specimens, the periphragm remains connected and in close contact with the endophragm (Pl. 1, fig. 3). In the poorly tabulated or untabulated specimens, the periphragm remains close to the endophragm, but is partially separated.
Holotype: Cookson and Eisenack, 1960b, pl.37, fig.9; Jan du Chêne et al., 1986a, pl.5, fig.1; pl.7, fig.6. Originally (and now) Scriniodinium, subsequently Scriniocassis, thirdly Aldorfia. This species was retained in Scriniodinium by Riding and Fensome (2003, p.16). Age: Oxfordian–Tithonian.
Original description: Cookson and Eisenack, 1960, p. 248
Shell flat, oval, divided by a +/- distinct and relatively broad girdle into an epitheca and hypotheca of approximately equal size; epitheca prolonged into a broadly based, short, blunt apical projection. Capsule oval with a short apical prominence. The wall of the capsule bears numerous thin perpendicular ledges which form a small-meshed supporting reticulum for the thin outer membrane. The meshes of the reticulum vary considerab]y in size and are usually widest towards the periphery. The pylome is broadly hoof-shaped and reaches the girdle.
Dimensions: holotype--109 µm long, 95 µm broad, capsule 95X83 µm.
Supplemental description of North Atlantic Specimens: Habib, 1974, p. 49
Proximate dinoflagellate cysts with polygonal to oval outline. Average W.L.R. 0.90; range from 0.79 to 1.00. Average C. I. 46; range from 45 to 51. Epitract with a short but prominent apical horn that may be open or closed distally; antapical horns lacking. Cingulum narrow, displaced one cingulum width or less. Cyst wall two layered. Periphragm membranous and irregularly reticulate or alveolate, supported by perforate septate sutures. Endophragm oval to polygonal in outline, but always closely approximating outline of cyst. Degree to which the cyst tabulation is expressed varies from almost absent to nearly complete plate formula 4", 0a, 6", 6c, 6""", 1p?, 1""""; plate boundaries incomplete adjacent to sulcus in otherwise well-tabulated specimens; expressed as sutural septa. Archeopyle precingular; formed by the loss of plate 3". Operculum simple and free. Maximum diameter of 45 specimens ranges from 85 to 120 µm; average 105 µm.
Affinities:
Habib, 1974, p. 49-50: The North Atlantic specimens of S. dictyotum differ from S. campanula only in the possession of an alveolate periphragm. They differ from the specimens of S. dictyotum described by Cookson and Eisenack (1960) in the evidence of cyst tabulation. The occurrence of relatively untabulated specimens as well, much like the holotype illustrated by Cookson and Eisenack, indicates that the degree to which the cyst tabulation is expressed varies intraspecifically. In the relatively well-tabulated specimens, the periphragm remains connected and in close contact with the endophragm (Pl. 1, fig. 3). In the poorly tabulated or untabulated specimens, the periphragm remains close to the endophragm, but is partially separated.