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Circulodinium compta
Circulodinium compta, (Davey, 1982), Helby, 1987
Davey, 1988, also transferred this species to Circulodinium.
Holotype: Davey 1982b: Pl. 8, figs. 3
Locus typicus: Sandringham Sands, Brook Farm, North Runcton, Norfolk, England.
Stratum typicum: Lamplughi Zone, Portlandian.
Age: Portlandian
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Original description as Canningia compta: [Davey 1982b, p. 26]:
Diagnosis:
Shape: Cysts subspherical to slightly angular with some dorso-ventral flattening. Apical region broadly conical; antapex rounded to slightly indented. Widest portion of the cyst is in the paracingular region.
Wall/Ornament: Wall of moderate thickness. Lightly pitted to foveolate and verrucate. Ornament less pronounced towards the centre of the dorsal postcingular paraplate and in the parasulcal region.
Paratabulation: Absent to poorly defined by relatively stronger ornamentation along the boundaries of the paracingulum on the dorsal surface and towards the margins of the dorsal postcingular paraplate. Parasulcus often defined by a distinct groove which extends across the ventral surface from the antapex towards the parasulcal notch and terminating in the paracingular region.
Archaeopyle: Apical; parasulcal notch strongly indented and offset to the left of the mid-line. Margin is strongly zig-zag.
Description:
The wall is approximately 1 to 1.5 µm in thickness (including ornament). The ornament is most easily observed in plan view and appears to consist of well developed verrucae. When the ornament is high it is noticeable at the lateral margins of the cyst but when low the cyst margins appear to be almost smooth. In the latter case it is probable that a foveolate wall structure is present.
Dimensions: Holotype (µm) Range (µm):
Pericyst length 68-82
Pericyst length (archaeopyle developed) 5454 (59) 65
Pericyst width 5252 (61) 74
Remarks:
The type of ornament, together with the strongly zig-zag archaeopyle margin with the deep parasulcal notch distinguishes C. compta sp. nov. from other members of this genus.
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Occurrence: C. compta occurs only rarely in the kerberus (formerly giganteus) Zone of Dorset and eastern England. However, it occurs abundantly in eastern England from the oppressus to stenomphalus Zone and typically makes up between 20 and 40% of the dinocyst assemblage; its greatest recorded abundance is in a sample from the primitivus Zone where it attains 74%. Undoubtedly, this species flourished in the relatively shallow shelfal seas established over eastern England during the Portlandian and the Ryazanian for it does not occur in the same abundance over most of the North Sea Basin. C. compta is rare in the albidum Zone and has only very rarely been recorded from the basal Valanginian. In Haldager No. 1 borehole C. compta is moderately to very common in cores 2866"-76" to 2989"-3009" (late Ryazanian to early Portlandian) and rarer at 2772"-82", 2832"-42", 3080"-3100" and 3180"-90". Thus the overall range here, as onshore, is early Valanginian to early Portlandian.
Davey, 1988, also transferred this species to Circulodinium.
Holotype: Davey 1982b: Pl. 8, figs. 3
Locus typicus: Sandringham Sands, Brook Farm, North Runcton, Norfolk, England.
Stratum typicum: Lamplughi Zone, Portlandian.
Age: Portlandian
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description as Canningia compta: [Davey 1982b, p. 26]:
Diagnosis:
Shape: Cysts subspherical to slightly angular with some dorso-ventral flattening. Apical region broadly conical; antapex rounded to slightly indented. Widest portion of the cyst is in the paracingular region.
Wall/Ornament: Wall of moderate thickness. Lightly pitted to foveolate and verrucate. Ornament less pronounced towards the centre of the dorsal postcingular paraplate and in the parasulcal region.
Paratabulation: Absent to poorly defined by relatively stronger ornamentation along the boundaries of the paracingulum on the dorsal surface and towards the margins of the dorsal postcingular paraplate. Parasulcus often defined by a distinct groove which extends across the ventral surface from the antapex towards the parasulcal notch and terminating in the paracingular region.
Archaeopyle: Apical; parasulcal notch strongly indented and offset to the left of the mid-line. Margin is strongly zig-zag.
Description:
The wall is approximately 1 to 1.5 µm in thickness (including ornament). The ornament is most easily observed in plan view and appears to consist of well developed verrucae. When the ornament is high it is noticeable at the lateral margins of the cyst but when low the cyst margins appear to be almost smooth. In the latter case it is probable that a foveolate wall structure is present.
Dimensions: Holotype (µm) Range (µm):
Pericyst length 68-82
Pericyst length (archaeopyle developed) 5454 (59) 65
Pericyst width 5252 (61) 74
Remarks:
The type of ornament, together with the strongly zig-zag archaeopyle margin with the deep parasulcal notch distinguishes C. compta sp. nov. from other members of this genus.
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Occurrence: C. compta occurs only rarely in the kerberus (formerly giganteus) Zone of Dorset and eastern England. However, it occurs abundantly in eastern England from the oppressus to stenomphalus Zone and typically makes up between 20 and 40% of the dinocyst assemblage; its greatest recorded abundance is in a sample from the primitivus Zone where it attains 74%. Undoubtedly, this species flourished in the relatively shallow shelfal seas established over eastern England during the Portlandian and the Ryazanian for it does not occur in the same abundance over most of the North Sea Basin. C. compta is rare in the albidum Zone and has only very rarely been recorded from the basal Valanginian. In Haldager No. 1 borehole C. compta is moderately to very common in cores 2866"-76" to 2989"-3009" (late Ryazanian to early Portlandian) and rarer at 2772"-82", 2832"-42", 3080"-3100" and 3180"-90". Thus the overall range here, as onshore, is early Valanginian to early Portlandian.