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Circulodinium araneosum

Circulodinium araneosum, (Brideaux, 1977, p.22-23, pl.9, figs.1-3), Fauconnier in Fauconnier and Masure, 2004, p.115.

Originally Cleistosphaeridium, subsequently Heterosphaeridium, thirdly (and now) Circulodinium?.
Questionable assignment: Fauconnier and Londeix in Fauconnier and Masure (2004, p.115-116).

Holotype: Brideaux, 1977, pl.9, figs.1-3.
Type locality: Horton River Formation
Age: Aptian-Albian.

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Diagnosis:
Shape: Pericyst subcircular; a short asymmetrical antapical prominence occurring on a few specimens. Endocyst as above, closely appressed to the pericyst. Pericoel not developed; compression dorso-ventral.
Phragma: Periphragm less than 0.5 μm thick, forming acuminate, distally pointed or weakly bifid processes up to 8 μm long and 0.5 to .0 μm wide, or flattened processes, wider basally and tapering distally, up to 10 μm long and up to 2.0 μm wide basally; process emplacement apparently non-paratabular; processes may or may not arise from a quasi-reticulate network of very low, narrow ridges formed of the periphragm, the ridges apparently also non-paratabular, process density highly variable, in places arranged in clusters. Surface ornamentation between processes scabrate to punctate. Endophragm less than 1.0 μm thick and unornamented.
Paratabulation: Archeopyle shape denotes four apical paraplates; other evidence for para tabulation lacking.
Archeopyle/operculum: Archeopyle formed by the loss of the four apical paraplates; operculum separating as a unit, simple and free, or lying in the archeopyle.
Formula: A.
Pericingulum/perisulcus: Pericingulum position determinable by parallel rows of widely spaced acuminate processes arising from a pair of narrow, low ridges formed from the periphragm; pericingulum positioned at the mid-latitude of the pericyst; pericingulum up to 7 μm wide and offset about one half of pericingular width. Evidence for a discernible perisulcus lacking.

Dimensions:
(15 μm measured specimens)
Pericyst length, 55-6 μm; pericyst width, 48-55 μm (maximum dimensions excluding processes). Maximum diameter on all reported specimens (see Brideaux , 1971; Brideaux and Mclntyre , 1976), 37-78 μm.
Pericyst length: 51μm pericyst width, 52 μm (excluding processes).

Affinities:
Cleistosphaeridium araneosum sp. nov. is distinguished from the comparable species, Cleistosphaeridium? aciculare Davey , 1969 and Cleistosphaeridium multispinosum (Singh) Brideaux, 1971 by possession of acuminate to weakly bifid spines arising from a low quasi-reticulate meshwork on the periphragm and by the much lower density of processes arising from the periphragm. Cleistosphaeridium multifurcatum (Deflandre) Davey et al., 1969, p. 16, differs in having a preponderance of distinctly bifid spines with broad columns arising from an obvermiculate surface ornament. Baltisphaeridium sp. A of Singh, 1971, p. 397, Plate 73, figures 9, 10, appears very similar, but Singh (1971, p. 397) characterizes the processes as " . .. splitting into numerous, slender, pointed spines at their outer ends...".

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Occurrence:
Rat Pass K-35: Upper sandstone division equivalent, sidewall cores and cuttings; Aptian. Stoney Core Hole F-42: Albian shale-siltstone division, Upper sandstone division and Upper shale-siltstone division equivalents, conventional core; Hauterivian to Middle Albian . Recorded previously from Middle and Upper Albian rocks of central and west-central Alberta, Canada (Brideaux , 1971) and from Middle Albian rocks on the Anderson Plain, northern Canadian mainland (Brideaux and Mclntyre , 1976). The suggestion of synonymy with Cleistosphaeridium? aciculare Davey (in part). is withdrawn and hence there is no confirmed Cenomanian record of Cleistosphaeridium araneosum sp. nov.
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