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Sentusidinium eisenackii
Sentusidinium eisenackii (Boltenhagen, 1977, p.56–58, pl.5, figs.5a–b,6a–b,7a–b,8a–b) Lentin and Williams, 1981, p.253.
Holotype: Boltenhagen, 1977, pl.5, figs.5a–b; Fauconnier and Masure, 2004, pl.69, fig.4.
Originally Tenua Eisenack, subsequently (and now) Sentusidinium. Taxonomic junior synonym: Sentusidinium spiculatum, according to Courtinat in Fauconnier and Masure (2004, p.485).
Age: Cenomanian–Turonian.
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Original description: [Boltenhagen, 1977] (translated from French):
Red Series, Cenomanian; Libreville (Gabon, Equatorial Africa).
DIAGNOSIS
Subspherical in shape with an infra-microgranular membrane, decorated with short, conical or more or less cylindrical elements, spaced, acuminate, or thickened at the top. The apical archaeopyle has zigzagging edges and is split at the re-entrant angles.
DESCRIPTION
Subspherical or oblong in shape, our specimens are characterized by a fairly thin membrane (± 11u), slightly punctuated at 320x magnification. At 800x magnification and immersion, the punctuation corresponds to infra-microgranulation. The shell surface is ornamented with thin spines and thick baculi, ranging in length from 1/15th to 1/25th of the shell diameter. Three main types can be distinguished: conical, cylindrical, and truncated, which are either acuminate or thickened at the apex in the shape of an inverted cone. Intermediate types are also observed. All these ornamental elements are fairly spaced and distributed evenly, so that there are no bare areas indicating a cingulate or sulcus.
The apical archaeopyle, with zigzagging edges, is affected by clefts at the re-entrant angles, which is typical of the genus in question.
DIMENSIONS
Holotype:
equatorial diameter: with ornamentation, d' = 84 μ
equatorial diameter: without ornamentation, d'' = 79 μ
polar axis including operculum, approximately 81 μ
polar axis of antapical cap, ± 63 μ
spines and baculi: L = 3 - 5 μ
Paratype:
equatorial diameter: with ornamentation, d' = 89 μ
equatorial diameter: without ornamentation, d'' = 84 μ
polar axis of antapical cap, 63 - 68 μ
spines and baculi: L = 2 - 4 μ
2 other specimens:
equatorial diameter: with ornamentation, d' = 74 and 86 μ
equatorial diameter: without ornamentation, d'' = 72 and 81 μ
polar axis: with ornamentation, 65 and 87 μ
polar axis: without ornamentation, 62 and 81 μ
spines and baculi: L = 3 - 5 μ
COMPARISON
The described species differs from the generotype Tenua hystrix EIS. 1958 (p. 410, PI. 23, Fig. 1-4; Fig. in-text 10) by the shape of the ornamental elements, which are, in proportion to the shell, much shorter; in particular, the acuminate spines are absent in the ornamentation of the generotype, which, on the other hand, has rods with primary and secondary bifurcations, not observed in the Gabonese specimens.
Our species is also distinguished from T. rioulti and T. villersense SAR. 1968 (pp. 231-232, PI. I, Figs. 16 and 22; PI. 2. Figs. 1, 2, 4, 5, and 10) by a pronounced maios ornamentation with more stocky elements, as well as by the absence of any indication of a cingulum and sulcus.
The difference with T. verrucosa SAR. 1968 (p. 232, PI. I, Figs. 17, 3 and 6) consists essentially in the shape of the ornamental elements and, as in the previous case, in the absence of individualization of a cingulum and a sulcus.
A resemblance exists between the ornamentation of our species and that of Chy troeisphaeridia spinosa nov. sp. described above. These two species are distinguished essentially by the shape of the archaeopyle.
Stratigraphic and Geographic Position
Upper Cretaceous: Turonian-Cenomanian; Gabon (Libreville - North Ogooué and Fernan-Vaz).
Holotype: Boltenhagen, 1977, pl.5, figs.5a–b; Fauconnier and Masure, 2004, pl.69, fig.4.
Originally Tenua Eisenack, subsequently (and now) Sentusidinium. Taxonomic junior synonym: Sentusidinium spiculatum, according to Courtinat in Fauconnier and Masure (2004, p.485).
Age: Cenomanian–Turonian.
----------------------------------------------------------------------------------------------------------------
Original description: [Boltenhagen, 1977] (translated from French):
Red Series, Cenomanian; Libreville (Gabon, Equatorial Africa).
DIAGNOSIS
Subspherical in shape with an infra-microgranular membrane, decorated with short, conical or more or less cylindrical elements, spaced, acuminate, or thickened at the top. The apical archaeopyle has zigzagging edges and is split at the re-entrant angles.
DESCRIPTION
Subspherical or oblong in shape, our specimens are characterized by a fairly thin membrane (± 11u), slightly punctuated at 320x magnification. At 800x magnification and immersion, the punctuation corresponds to infra-microgranulation. The shell surface is ornamented with thin spines and thick baculi, ranging in length from 1/15th to 1/25th of the shell diameter. Three main types can be distinguished: conical, cylindrical, and truncated, which are either acuminate or thickened at the apex in the shape of an inverted cone. Intermediate types are also observed. All these ornamental elements are fairly spaced and distributed evenly, so that there are no bare areas indicating a cingulate or sulcus.
The apical archaeopyle, with zigzagging edges, is affected by clefts at the re-entrant angles, which is typical of the genus in question.
DIMENSIONS
Holotype:
equatorial diameter: with ornamentation, d' = 84 μ
equatorial diameter: without ornamentation, d'' = 79 μ
polar axis including operculum, approximately 81 μ
polar axis of antapical cap, ± 63 μ
spines and baculi: L = 3 - 5 μ
Paratype:
equatorial diameter: with ornamentation, d' = 89 μ
equatorial diameter: without ornamentation, d'' = 84 μ
polar axis of antapical cap, 63 - 68 μ
spines and baculi: L = 2 - 4 μ
2 other specimens:
equatorial diameter: with ornamentation, d' = 74 and 86 μ
equatorial diameter: without ornamentation, d'' = 72 and 81 μ
polar axis: with ornamentation, 65 and 87 μ
polar axis: without ornamentation, 62 and 81 μ
spines and baculi: L = 3 - 5 μ
COMPARISON
The described species differs from the generotype Tenua hystrix EIS. 1958 (p. 410, PI. 23, Fig. 1-4; Fig. in-text 10) by the shape of the ornamental elements, which are, in proportion to the shell, much shorter; in particular, the acuminate spines are absent in the ornamentation of the generotype, which, on the other hand, has rods with primary and secondary bifurcations, not observed in the Gabonese specimens.
Our species is also distinguished from T. rioulti and T. villersense SAR. 1968 (pp. 231-232, PI. I, Figs. 16 and 22; PI. 2. Figs. 1, 2, 4, 5, and 10) by a pronounced maios ornamentation with more stocky elements, as well as by the absence of any indication of a cingulum and sulcus.
The difference with T. verrucosa SAR. 1968 (p. 232, PI. I, Figs. 17, 3 and 6) consists essentially in the shape of the ornamental elements and, as in the previous case, in the absence of individualization of a cingulum and a sulcus.
A resemblance exists between the ornamentation of our species and that of Chy troeisphaeridia spinosa nov. sp. described above. These two species are distinguished essentially by the shape of the archaeopyle.
Stratigraphic and Geographic Position
Upper Cretaceous: Turonian-Cenomanian; Gabon (Libreville - North Ogooué and Fernan-Vaz).