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Wilsonidium stellatum
Wilsonidinium stellatum Antolinez-Delgado and Oboh-Ikuenobe, 2007, p.60–61, pl.2, figs.1–2,6,8.
Holotype: Antolinez-Delgado and Oboh-Ikuenobe, 2007, pl.2, fig.1.
Age: Paleocene–?earliest Eocene.
Original description (Antolinez-Delgado and Oboh-Ikuenobe, 2007)
Derivation of name. From the Latin stellatus, resembling a star, with reference to the outline of the cyst.
Holotype. Plate 2, figure 1, slide R-1134-3, Lovins finder coordinates 3Q/R. Alo-1 well, 109.7 m, Upper Paleocene. Dimensions: length, including apical and antapical horns, 103 μm; width, including lateral horns, 90 μm; length of apical horn 35 μm; length of lateral horns 33 μm; length of antapical horns 28 μm.
Diagnosis. A species of Wilsonidium with a cornucavate cyst, well developed apical, lateral and antapical horns, and a trapezoidal archeopyle.
Description. Proximate peridinacean dinoflagellate cysts, bilaterally asymmetrical, cornucavate, with one apical horn, two lateral horns and two antapical horns. All horns are prominent, tapered and pointed, giving the cyst a radiate or stellate outline. Relative sizes between the horns are variable in each specimen. Left antapical horn occasionally shorter or thinner than the right antapical horn, although there is usually only a small difference. The endocyst is pentagonal, with smooth walls. Periphragm smooth, bearing sutural ridges supporting numerous short processes (<4 μm), that may be acuminate or bifid. Continuity of sutural ridges on the surface of the cyst is variable and in some specimens is only clearly discernible on the ambitus and the surface of the horns. Cingulum and sulcus are not clearly quadra-style, defined. Archeopyle intercalary, type I/I2a shape trapezoidal, usually difficult to observe.
Dimensions. Length, including apical and antapical horns, 85–105 μm; width, including lateral horns, 80–110 μm; length of the apical horn 15–35 μm; length of the lateral horns 25–33 μm; length of the antapical horns 25–30 μm (7 specimens measured).
Comparison. Wilsonidium stellatum sp. nov. differs from Wilsonidium echinosuturatum (Wilson 1967) Lentin & Williams 1976, Wilsonidium ornatum (Wilson 1967) Lentin & Williams 1976, and Wilsonidium tabulatum (Wilson 1967) Lentin & Williams 1976, in being cornucavate, with well-developed apical, lateral and antapical horns, and in having a trapezoidal archeopyle. Wilsonidium tabulatum also has well-developed horns at each angle but is a circumcavate, rather than a cornucavate, cyst and has a square to rectangular archeopyle. Wilsonidium echinosuturatum has much shorter horns and a rectangular archeopyle. Wilsonidium ornatum has a trapezoidal archeopyle, but a different surface ornament with “…rectangular pillars arranged in rows and usually capped by a fairly short membranous fibre” (Wilson, 1967; p. 481), that do not emerge from the sutural ridges. Wilsonidium nigeriaense Jan du Chêne & Adediran 1985 has a rectangular archeopyle, and short processes connected distally by an undulose fringe. The processes in Wilsonidium stellatum sp. nov. are not connected distally.
Stratigraphic range. Wilsonidium stellatum sp. nov. was observed in the Alo-1 well from 109.7 m to 201 m.
Holotype: Antolinez-Delgado and Oboh-Ikuenobe, 2007, pl.2, fig.1.
Age: Paleocene–?earliest Eocene.
Original description (Antolinez-Delgado and Oboh-Ikuenobe, 2007)
Derivation of name. From the Latin stellatus, resembling a star, with reference to the outline of the cyst.
Holotype. Plate 2, figure 1, slide R-1134-3, Lovins finder coordinates 3Q/R. Alo-1 well, 109.7 m, Upper Paleocene. Dimensions: length, including apical and antapical horns, 103 μm; width, including lateral horns, 90 μm; length of apical horn 35 μm; length of lateral horns 33 μm; length of antapical horns 28 μm.
Diagnosis. A species of Wilsonidium with a cornucavate cyst, well developed apical, lateral and antapical horns, and a trapezoidal archeopyle.
Description. Proximate peridinacean dinoflagellate cysts, bilaterally asymmetrical, cornucavate, with one apical horn, two lateral horns and two antapical horns. All horns are prominent, tapered and pointed, giving the cyst a radiate or stellate outline. Relative sizes between the horns are variable in each specimen. Left antapical horn occasionally shorter or thinner than the right antapical horn, although there is usually only a small difference. The endocyst is pentagonal, with smooth walls. Periphragm smooth, bearing sutural ridges supporting numerous short processes (<4 μm), that may be acuminate or bifid. Continuity of sutural ridges on the surface of the cyst is variable and in some specimens is only clearly discernible on the ambitus and the surface of the horns. Cingulum and sulcus are not clearly quadra-style, defined. Archeopyle intercalary, type I/I2a shape trapezoidal, usually difficult to observe.
Dimensions. Length, including apical and antapical horns, 85–105 μm; width, including lateral horns, 80–110 μm; length of the apical horn 15–35 μm; length of the lateral horns 25–33 μm; length of the antapical horns 25–30 μm (7 specimens measured).
Comparison. Wilsonidium stellatum sp. nov. differs from Wilsonidium echinosuturatum (Wilson 1967) Lentin & Williams 1976, Wilsonidium ornatum (Wilson 1967) Lentin & Williams 1976, and Wilsonidium tabulatum (Wilson 1967) Lentin & Williams 1976, in being cornucavate, with well-developed apical, lateral and antapical horns, and in having a trapezoidal archeopyle. Wilsonidium tabulatum also has well-developed horns at each angle but is a circumcavate, rather than a cornucavate, cyst and has a square to rectangular archeopyle. Wilsonidium echinosuturatum has much shorter horns and a rectangular archeopyle. Wilsonidium ornatum has a trapezoidal archeopyle, but a different surface ornament with “…rectangular pillars arranged in rows and usually capped by a fairly short membranous fibre” (Wilson, 1967; p. 481), that do not emerge from the sutural ridges. Wilsonidium nigeriaense Jan du Chêne & Adediran 1985 has a rectangular archeopyle, and short processes connected distally by an undulose fringe. The processes in Wilsonidium stellatum sp. nov. are not connected distally.
Stratigraphic range. Wilsonidium stellatum sp. nov. was observed in the Alo-1 well from 109.7 m to 201 m.