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Cleistosphaeridium clavulum
Cleistosphaeridium clavulum, (Davey, 1969), Below, 1982
NOW Impletosphaeridium clavulum. Originally Cleistosphaeridium polypes var. clavulum, subsequently Cleistosphaeridium polypes subsp. clavulum, thirdly Impletosphaeridium polypes subsp. clavulum, fourthly Bacchidinium polypes subsp. clavulum, fifthly Cleistosphaeridium clavulum, sixthly (and now) Impletosphaeridium clavulum.
This taxon was raised to the subspecies level by Lentin and Williams, 1973. It was raised to the species level by Below, 1982, as Cleistosphaeridium clavulum.
Holotype: Davey, 1969a: Pl. 6, fig. 9
Locus typicus: Lower Chalk, H.M. Geological Survey Borehole, Fetcham Mill, Surrey
Stratum typicum: Upper Cretaceous (Cenomanian).
Occurrence: lowermost Cenomanian samples at Fetcham Mill (sample FM 840) and Compton Bay (sample CB I); previously recorded by Cookson & Hughes (I964) from the Upper Albian-basal Cenomanian of England and so appears to be of stratigraphic importance in England for indicating the base of this stage; does not occur in the lowermost sample from Escalles.
Age: Cenomanian
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Original description as Cleistosphaeridium polypes var. clavulum: [Davey 1969a, p. 154, 155]:
Diagnosis:
A variety of C. polypes possessing fine, capitate processes. Processes terminating with fine spines are extremely rare.
Dimensions:
Type: diameter of central body 29 by 32 µm, length of processes 12-13 µm.
Range: diameter of central body 29 (31.5) 39 µm, maximum length of processes 13 (14.7) 15 µm. Numbers of specimens measured: 10.
Remarks:
C. polypes var. clavulum differs from C. polypes in that the processes are capitate, the terminal bulge being flattened and resembling the head of a pin. Two specimens have been observed each possessing one process of the type characteristic of C. polypes thus indicating a relationship between the two forms. C. polypes probably evolved from this variety, spiny processes replacing the capitate ones.
NOW Impletosphaeridium clavulum. Originally Cleistosphaeridium polypes var. clavulum, subsequently Cleistosphaeridium polypes subsp. clavulum, thirdly Impletosphaeridium polypes subsp. clavulum, fourthly Bacchidinium polypes subsp. clavulum, fifthly Cleistosphaeridium clavulum, sixthly (and now) Impletosphaeridium clavulum.
This taxon was raised to the subspecies level by Lentin and Williams, 1973. It was raised to the species level by Below, 1982, as Cleistosphaeridium clavulum.
Holotype: Davey, 1969a: Pl. 6, fig. 9
Locus typicus: Lower Chalk, H.M. Geological Survey Borehole, Fetcham Mill, Surrey
Stratum typicum: Upper Cretaceous (Cenomanian).
Occurrence: lowermost Cenomanian samples at Fetcham Mill (sample FM 840) and Compton Bay (sample CB I); previously recorded by Cookson & Hughes (I964) from the Upper Albian-basal Cenomanian of England and so appears to be of stratigraphic importance in England for indicating the base of this stage; does not occur in the lowermost sample from Escalles.
Age: Cenomanian
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Original description as Cleistosphaeridium polypes var. clavulum: [Davey 1969a, p. 154, 155]:
Diagnosis:
A variety of C. polypes possessing fine, capitate processes. Processes terminating with fine spines are extremely rare.
Dimensions:
Type: diameter of central body 29 by 32 µm, length of processes 12-13 µm.
Range: diameter of central body 29 (31.5) 39 µm, maximum length of processes 13 (14.7) 15 µm. Numbers of specimens measured: 10.
Remarks:
C. polypes var. clavulum differs from C. polypes in that the processes are capitate, the terminal bulge being flattened and resembling the head of a pin. Two specimens have been observed each possessing one process of the type characteristic of C. polypes thus indicating a relationship between the two forms. C. polypes probably evolved from this variety, spiny processes replacing the capitate ones.