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Ascodinium verrucosum ssp. ostium
Ascodinium verrucosum ssp. ostium, (Davey, 1970), Lentin and Williams, 1985
NOW Ovoidinium verrucosum subsp. ostium. Originally Ovoidinium ostium, subsequently Ovoidinium verrucosum var. ostium, thirdly (and now) Ovoidinium verrucosum subsp. ostium, fourthly Ascodinium verrucosum subsp. ostium.
Holotype: Davey, 1970, pl.4, fig.5
Occurrence: only recorded from Saskatchewan, in samples Sas1084 and 1023 (Albian), and samples Sas890 (Lower Cenomanian); fairly common in the lower two samples but rare in the Cenomanian sample.
Age: Albian-Early Cenomanian
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Original description: [Davey, 1970]:
Diagnosis:
inner body subspherical, lightly but densely granular, with moderately thick wall. Periphargm slightly granular, sometimes bearing tubereles. Apical pericoel small, with poorly developed horn; posterior pericoel asymmetrical, possessing sub-rectangular opening on ventral surface. Cingulum and sulcus moderately to well-defined. Apical region generally lost in archaeopyle formation.
Description:
The inner body wall (1-1.5 μm thick) is surrounded by an outer membrane (approximately 0.5 μm thick), the two being in contact only in the cingular region. A characteristic sub-rectangular shaped opening is always developed on the ventral surface of the posterior pericoel membrane (text-fig. 1B). The opening lies towards the posterior end of the sulcus and is typically closed by an operculum.
The operculum of the apical archeopyle is usually detached and the archaeopyle margin is only slightly angular.
Dimensions:
Holotype: overall length 59 μm, length of inner body 39 μm, width of inner body 40 μm.
Paratype: length (operculum missing) 50 μm, length of inner body 35 μm, width of inner body 48 μm.
Range: length (operculum missing) 37(46.2) 63 μm, length of inner body 28 (34.4) 45 μm, width of inner body 37 (43.1) 54 μm. Number of specimens measured, 9.
Remarks:
O. ostium sp. nov. is similar to O. scabrosum and O. verrusosum and tends to grade into the one or the other depending on the form of ornamentation. The opening is the posterior pericoel membrane, however, is distinctive and quite characteristic. The operculum closing this opening is always attached and, therefore, acted as a lid. The purpose of this structure can only be surmised. The most probable explanation is perhaps that this opening allowed seawater into the posterior pericoel so regulating the buoyancy of the cyst in some manner’.
NOW Ovoidinium verrucosum subsp. ostium. Originally Ovoidinium ostium, subsequently Ovoidinium verrucosum var. ostium, thirdly (and now) Ovoidinium verrucosum subsp. ostium, fourthly Ascodinium verrucosum subsp. ostium.
Holotype: Davey, 1970, pl.4, fig.5
Occurrence: only recorded from Saskatchewan, in samples Sas1084 and 1023 (Albian), and samples Sas890 (Lower Cenomanian); fairly common in the lower two samples but rare in the Cenomanian sample.
Age: Albian-Early Cenomanian
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Davey, 1970]:
Diagnosis:
inner body subspherical, lightly but densely granular, with moderately thick wall. Periphargm slightly granular, sometimes bearing tubereles. Apical pericoel small, with poorly developed horn; posterior pericoel asymmetrical, possessing sub-rectangular opening on ventral surface. Cingulum and sulcus moderately to well-defined. Apical region generally lost in archaeopyle formation.
Description:
The inner body wall (1-1.5 μm thick) is surrounded by an outer membrane (approximately 0.5 μm thick), the two being in contact only in the cingular region. A characteristic sub-rectangular shaped opening is always developed on the ventral surface of the posterior pericoel membrane (text-fig. 1B). The opening lies towards the posterior end of the sulcus and is typically closed by an operculum.
The operculum of the apical archeopyle is usually detached and the archaeopyle margin is only slightly angular.
Dimensions:
Holotype: overall length 59 μm, length of inner body 39 μm, width of inner body 40 μm.
Paratype: length (operculum missing) 50 μm, length of inner body 35 μm, width of inner body 48 μm.
Range: length (operculum missing) 37(46.2) 63 μm, length of inner body 28 (34.4) 45 μm, width of inner body 37 (43.1) 54 μm. Number of specimens measured, 9.
Remarks:
O. ostium sp. nov. is similar to O. scabrosum and O. verrusosum and tends to grade into the one or the other depending on the form of ornamentation. The opening is the posterior pericoel membrane, however, is distinctive and quite characteristic. The operculum closing this opening is always attached and, therefore, acted as a lid. The purpose of this structure can only be surmised. The most probable explanation is perhaps that this opening allowed seawater into the posterior pericoel so regulating the buoyancy of the cyst in some manner’.