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Svalbardella clausii
Svalbardella clausii sp. nov., Sliwinska and Head, 2020
Holotype: Sliwinska and Head, 2020, Slide 158L-2
Type locality: eastern North Sea basin
Age: mid-Oligocene
Original description: Sliwinska and Head, 2020:
Diagnosis:
A species of Svalbardella with rounded, short apical and antapical horns of approximately equal length. The endocyst is broad with a length approximately 1.5 times the width. The endocyst is ellipsoidal and has a smooth wall. The periphragm is nearly smooth to microrugulate or incompletely microreticulate. On more coarsely ornamented specimens, tabulation may be expressed by the cingulum and/or plates 1a, 3a, 3–5′′, and/or 1–2′′′′ in addition to the archeopyle. The archeopyle is intercalary type I (2a); adcingular margin of the periarcheopyle slightly overlaps that of the endoarcheopyle (operculum free).
Description:
A fusiform peridiniacean species with apex and antapex, each having a single short and bluntly rounded horn. The cyst is long, wide, and cornucavate. The endocyst is ellipsoidal and has a smooth wall.
Wall: periphragm is nearly smooth to faintly or conspicuously ornamented with a microrugulate pattern that may include discrete and partially fused granules and may develop into an incomplete microreticulation.
The endophragm and periphragm are appressed except at the horns. The horns are rounded to bulbous in shape. A small tapering antapical or apical protuberance up to 7 μm long may occur at the termination of a horn (marked by an arrow in Plate 1E and H). Horns are approximately equal in length, and each is generally less than 30 % of the endocyst length.
Tabulation: When the periphragm is nearly smooth, the tabulation is expressed only by the archeopyle. On more coarsely ornamented specimens, the tabulation may be expressed by the cingulum and/or plates 1a, 3a, 3–5′′, and/or 1–2′′′′ in addition to the archeopyle.
Archeopyle: intercalary type I (2a), isodeltaform (operculum free). The periarcheopyle is of
similar size or slightly larger than the endoarcheopyle. The adcingular margin of the periarcheopyle is up to ∼ 1.5 μm higher than that of the endoarcheopyle (Plate 1F).
Dimensions:
Holotype: endocyst length 87 μm; pericyst length 122 μm; width 57 μm; apical horn length 20 μm; antapical horn length 20 μm. Range (n = 12): endocyst length 75–98 μm (mean 85.2 μm); pericyst length 100–150 μm (mean 120.2 μm); width 52–65 μm (mean 57.5 μm); apical horn length 12–25 μm (mean 19.4 μm); antapical horn length 15–30 μm (mean 20.2 μm).
Affinities/Comparison:
Svalbardella partimtabulata is significantly more slender, has a smaller endocyst, and relatively longer horns, with the antapical horn being significantly longer than the apical horn. Svalbardella cooksoniae has a slightly longer but significantly narrower endocyst and longer and more conical horns in contrast with the short, almost bulbous horns in Svalbardella clausii. Palaeocystodinium obesum is also broad and has very short horns, but they are pointed and slightly smaller in size. However, forms transitional between Palaeocystodinium obesum and Svalbardella clausii sp. nov. (Plate 5D) have been observed in the lower Chattian in the western North Atlantic (e.g. IODP Hole U1406B, Sample 342-U1406B-17-4; 76–79 cm).
Holotype: Sliwinska and Head, 2020, Slide 158L-2
Type locality: eastern North Sea basin
Age: mid-Oligocene
Original description: Sliwinska and Head, 2020:
Diagnosis:
A species of Svalbardella with rounded, short apical and antapical horns of approximately equal length. The endocyst is broad with a length approximately 1.5 times the width. The endocyst is ellipsoidal and has a smooth wall. The periphragm is nearly smooth to microrugulate or incompletely microreticulate. On more coarsely ornamented specimens, tabulation may be expressed by the cingulum and/or plates 1a, 3a, 3–5′′, and/or 1–2′′′′ in addition to the archeopyle. The archeopyle is intercalary type I (2a); adcingular margin of the periarcheopyle slightly overlaps that of the endoarcheopyle (operculum free).
Description:
A fusiform peridiniacean species with apex and antapex, each having a single short and bluntly rounded horn. The cyst is long, wide, and cornucavate. The endocyst is ellipsoidal and has a smooth wall.
Wall: periphragm is nearly smooth to faintly or conspicuously ornamented with a microrugulate pattern that may include discrete and partially fused granules and may develop into an incomplete microreticulation.
The endophragm and periphragm are appressed except at the horns. The horns are rounded to bulbous in shape. A small tapering antapical or apical protuberance up to 7 μm long may occur at the termination of a horn (marked by an arrow in Plate 1E and H). Horns are approximately equal in length, and each is generally less than 30 % of the endocyst length.
Tabulation: When the periphragm is nearly smooth, the tabulation is expressed only by the archeopyle. On more coarsely ornamented specimens, the tabulation may be expressed by the cingulum and/or plates 1a, 3a, 3–5′′, and/or 1–2′′′′ in addition to the archeopyle.
Archeopyle: intercalary type I (2a), isodeltaform (operculum free). The periarcheopyle is of
similar size or slightly larger than the endoarcheopyle. The adcingular margin of the periarcheopyle is up to ∼ 1.5 μm higher than that of the endoarcheopyle (Plate 1F).
Dimensions:
Holotype: endocyst length 87 μm; pericyst length 122 μm; width 57 μm; apical horn length 20 μm; antapical horn length 20 μm. Range (n = 12): endocyst length 75–98 μm (mean 85.2 μm); pericyst length 100–150 μm (mean 120.2 μm); width 52–65 μm (mean 57.5 μm); apical horn length 12–25 μm (mean 19.4 μm); antapical horn length 15–30 μm (mean 20.2 μm).
Affinities/Comparison:
Svalbardella partimtabulata is significantly more slender, has a smaller endocyst, and relatively longer horns, with the antapical horn being significantly longer than the apical horn. Svalbardella cooksoniae has a slightly longer but significantly narrower endocyst and longer and more conical horns in contrast with the short, almost bulbous horns in Svalbardella clausii. Palaeocystodinium obesum is also broad and has very short horns, but they are pointed and slightly smaller in size. However, forms transitional between Palaeocystodinium obesum and Svalbardella clausii sp. nov. (Plate 5D) have been observed in the lower Chattian in the western North Atlantic (e.g. IODP Hole U1406B, Sample 342-U1406B-17-4; 76–79 cm).