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Cladopyxidium foveolatum
Cladopyxidium foveolatum, McMinn, 1988, p.148-150, figs.5A-F,6A-B; Emendation: Marheinecke, 1992, p.105.
Holotype: McMinn, 1988, figs.5A,C,E; Fensome et al., 1996, figs.1-3 - p.2131.
Occurrence: Rare to common in the Deflandrea diebelii and A lisocysta circumtabulata Zones (Maastrichtian) of the Carnarvon, Canning, Browse and Bonaparte Basins.
Age: Maastrichtian
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Original description: [McMinn, 1988]:
Description:
Small, single-layered, proximate, subspherical to ovoid cyst.
The autophragm is 1-2 µm thick, finely granular and also foveolate. The foveolate appearance arises from the many, very fine, perforations, which are approximately 3 µm apart.
Parasutural crests, 4(3)2 µm high, clearly express the paratabulation. Intratabular accessory ridges or grana present on many specimens sometimes develop into an incomplete reticulum.
The paratabulation formula is interpreted as ?4', 3a, 6"", 6c, 6""', lp, t"""", 5s. Four small paraplates are recognized on the anterior portion of the parasulcus while the posterior part of the parasulcus appears to consist of a single, large posterior sulcal paraplate.
Most specimens have a subcircular archeopyle (?type 2A) with a thickened apical rim. Paraplates 1' and 4' are usually present and so presumably only paraplates 2' and 3' are lost in archeopyle formation. Less frequently specimens also lose paraplates 1' and 4' (archeopyle type tA); these specimens also seem to lack the thickened apical rim. As no opercular pieces have been found, however, it has not been possible to determine the exact manner in which the archeopyle developed.
Dimensions:
Autocyst (excluding septa); length 30(26)25 µm, width 27(24)22 µm. Twenty specimens were measured.
Remarks:
Cladopyxidium foveolatum has archeopyle characteristics pitermediate between Microdinium Cookson & Eisenack 1960, which has a [tA] or [tAtI] archeopyle, and Cladopyxidium, which has a 2A archeopyle. It is assigned to ladopyxidium, however, because of the thickened subcircular apical margin and the retention of paraplates 1' and 4' on most specimens.
Affinities:
The development of intratabular sculpture on Cladopyxidium foveolatum is variable and specimens on which it is particularly well developed are often difficult to distinguish from Palaeostomocystis reticulata. The latter, however, is usually thinner, smaller and has a finer reticulum than Cladopyxiclium foveotatum. Cladopyxidium foveolatum can be distinguished from Cladopyxidium saeptum (Morgenroth) Stover & Evitt 1978 by the presence of a foveolate autophragm. There is also a close similarity between Cladopyxidium foveolatum and Microdinium ? punctulatum Vozzhennikova 1967, as both species are similar in size, have a granular autophragm, parasutural crests and an apical archeopyle. The main difference between these two species is the apparent absence of anterior intercalary paraplates on M. ? punctulatum.
Holotype: McMinn, 1988, figs.5A,C,E; Fensome et al., 1996, figs.1-3 - p.2131.
Occurrence: Rare to common in the Deflandrea diebelii and A lisocysta circumtabulata Zones (Maastrichtian) of the Carnarvon, Canning, Browse and Bonaparte Basins.
Age: Maastrichtian
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [McMinn, 1988]:
Description:
Small, single-layered, proximate, subspherical to ovoid cyst.
The autophragm is 1-2 µm thick, finely granular and also foveolate. The foveolate appearance arises from the many, very fine, perforations, which are approximately 3 µm apart.
Parasutural crests, 4(3)2 µm high, clearly express the paratabulation. Intratabular accessory ridges or grana present on many specimens sometimes develop into an incomplete reticulum.
The paratabulation formula is interpreted as ?4', 3a, 6"", 6c, 6""', lp, t"""", 5s. Four small paraplates are recognized on the anterior portion of the parasulcus while the posterior part of the parasulcus appears to consist of a single, large posterior sulcal paraplate.
Most specimens have a subcircular archeopyle (?type 2A) with a thickened apical rim. Paraplates 1' and 4' are usually present and so presumably only paraplates 2' and 3' are lost in archeopyle formation. Less frequently specimens also lose paraplates 1' and 4' (archeopyle type tA); these specimens also seem to lack the thickened apical rim. As no opercular pieces have been found, however, it has not been possible to determine the exact manner in which the archeopyle developed.
Dimensions:
Autocyst (excluding septa); length 30(26)25 µm, width 27(24)22 µm. Twenty specimens were measured.
Remarks:
Cladopyxidium foveolatum has archeopyle characteristics pitermediate between Microdinium Cookson & Eisenack 1960, which has a [tA] or [tAtI] archeopyle, and Cladopyxidium, which has a 2A archeopyle. It is assigned to ladopyxidium, however, because of the thickened subcircular apical margin and the retention of paraplates 1' and 4' on most specimens.
Affinities:
The development of intratabular sculpture on Cladopyxidium foveolatum is variable and specimens on which it is particularly well developed are often difficult to distinguish from Palaeostomocystis reticulata. The latter, however, is usually thinner, smaller and has a finer reticulum than Cladopyxiclium foveotatum. Cladopyxidium foveolatum can be distinguished from Cladopyxidium saeptum (Morgenroth) Stover & Evitt 1978 by the presence of a foveolate autophragm. There is also a close similarity between Cladopyxidium foveolatum and Microdinium ? punctulatum Vozzhennikova 1967, as both species are similar in size, have a granular autophragm, parasutural crests and an apical archeopyle. The main difference between these two species is the apparent absence of anterior intercalary paraplates on M. ? punctulatum.