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Cleistosphaeridium araneosum

Cleistosphaeridium araneosum, Brideaux, 1977

NOW Circulodinium?. Originally Cleistosphaeridium, subsequently Heterosphaeridium, thirdly (and now) Circulodinium?.

Holotype: Brideaux, 1977, pl.9, 1-2
Locus typicus: Richardson Mountains, District of Mackenzie, Canada
Stratum typicum: Aptian-Albian

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Original description: [Brideaux, 1977, p. 22-23]:

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 1.0 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 paratabulation 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.
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:
Pericyst length, 55-63 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.

Affinities:
Cleistosphaeridium araneosum is distinguished from the comparable species Cleistosphaeridium? acilare 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 differs in having a preponderance of distinctly bifid spines with broad columns arising from an obvermiculate surface ornament. Baltisphaeridium sp. A of Singh, 1971, 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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