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Impagidinium gibrense
From Fensome et al., 2019:
Impagidinium gibrense Michoux, 1985, p.145, pl.1, figs.5–8,13–14; pl.2, fig.10; text-fig.5. Holotype: Michoux, 1985, pl.1, figs.5–
6; Jan du Chêne et al., 1986a, pl.57, figs.1–5. Age: Early to Middle Eocene.
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Original description: [Michoux, 1985] (translated from French):
Impagidinium gibrensis n. sp.
(Pl. 1, fig. 5-6, 7-8, 13, 14; Pl. 2, fig. 10; text-fig. 5)
Holotype: Slide G1-2, coordinates H 48-2.
Name origin: From the Gibret locality.
Type locality: Section from Gibret, marl-limestone from the base of the Nousse Beds.
Diagnosis: Species of the genus Impagidinium, characterized by a spherical central body with a smooth surface, without an apical horn, adorned with parasutural ridges expressed over the entire surface of the cyst, except for the sulcus.
Description: Spherical cyst, bearing low parasutural septa, 3 to 6 µm high, with a slightly sinuous edge. The surface of the cyst appears smooth, both under light and electron microscopy. The tabulation is marked by parasutural ridges. The septum laterally separating the 1' and 4' plates is poorly or not at all developed. The 1'" plate, narrow and rectangular in shape, is separated from the sulcus only by a short posterior septum (Pl. 1, fig. 14; text-fig. 5). The sulcus is wide and extends from the apex to the antapex. It is not divided transversely, except by a septum delimiting the posterior sulcal plate, which may be only incipient (Pl. 1, fig. 14) or fully developed (Pl. 2, fig. 10). The archaeopyle is reduced (the operculum does not occupy the entire surface of plate 3). This characteristic is clearly visible on the SEM image of figure 13, plate 1.
Tabulation: 4', 6", 6c, 6'", 1p, ps, 1"".
Dimensions: Diameter of the central body: 45 (56) 70 μm; septa height: 3 to 6 μm; 14 specimens measured.
Discussion: Impagidinium dispertitum (COOKSON and EISENACK) STOVER and EVITT, 1978 is similar to Impagidinium gibrensis n. sp. in shape and size, but differs in the presence of transverse septa dividing the sulcus. I. victorianum (COOKSON and EISENACK) STOVER and EVITT, 1978 lacks septa separating cingulate paraplates 1c and 6c from the underlying postcingulate paraplates. I. gibrensis is comparable to I. californiense DAMASSA, 1979 in size, ridge height, smooth cyst surface, and reduced archaeopyle. However, I. californiense differs in greater development of the ridges. parasuturals in the sulcus region, which allows the recognition of 5 sulcal paraplates.
Impagidinium gibrense Michoux, 1985, p.145, pl.1, figs.5–8,13–14; pl.2, fig.10; text-fig.5. Holotype: Michoux, 1985, pl.1, figs.5–
6; Jan du Chêne et al., 1986a, pl.57, figs.1–5. Age: Early to Middle Eocene.
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Original description: [Michoux, 1985] (translated from French):
Impagidinium gibrensis n. sp.
(Pl. 1, fig. 5-6, 7-8, 13, 14; Pl. 2, fig. 10; text-fig. 5)
Holotype: Slide G1-2, coordinates H 48-2.
Name origin: From the Gibret locality.
Type locality: Section from Gibret, marl-limestone from the base of the Nousse Beds.
Diagnosis: Species of the genus Impagidinium, characterized by a spherical central body with a smooth surface, without an apical horn, adorned with parasutural ridges expressed over the entire surface of the cyst, except for the sulcus.
Description: Spherical cyst, bearing low parasutural septa, 3 to 6 µm high, with a slightly sinuous edge. The surface of the cyst appears smooth, both under light and electron microscopy. The tabulation is marked by parasutural ridges. The septum laterally separating the 1' and 4' plates is poorly or not at all developed. The 1'" plate, narrow and rectangular in shape, is separated from the sulcus only by a short posterior septum (Pl. 1, fig. 14; text-fig. 5). The sulcus is wide and extends from the apex to the antapex. It is not divided transversely, except by a septum delimiting the posterior sulcal plate, which may be only incipient (Pl. 1, fig. 14) or fully developed (Pl. 2, fig. 10). The archaeopyle is reduced (the operculum does not occupy the entire surface of plate 3). This characteristic is clearly visible on the SEM image of figure 13, plate 1.
Tabulation: 4', 6", 6c, 6'", 1p, ps, 1"".
Dimensions: Diameter of the central body: 45 (56) 70 μm; septa height: 3 to 6 μm; 14 specimens measured.
Discussion: Impagidinium dispertitum (COOKSON and EISENACK) STOVER and EVITT, 1978 is similar to Impagidinium gibrensis n. sp. in shape and size, but differs in the presence of transverse septa dividing the sulcus. I. victorianum (COOKSON and EISENACK) STOVER and EVITT, 1978 lacks septa separating cingulate paraplates 1c and 6c from the underlying postcingulate paraplates. I. gibrensis is comparable to I. californiense DAMASSA, 1979 in size, ridge height, smooth cyst surface, and reduced archaeopyle. However, I. californiense differs in greater development of the ridges. parasuturals in the sulcus region, which allows the recognition of 5 sulcal paraplates.