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Cladopyxidium foveolatum
From Fensome et al., 2019:
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. 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.
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Emendation Marheinecke, 1992 (p. 105) (translated from German):
Emended description: Cyst habit proximochorate, acavate, ovaloid to almost spheroidal, small to very small. Wall consisting of pedium and luxuria, which distally forms a tegillum. Tegillum scabrately pierced by irregularly distributed pores. The tegillum forms finite septa of approximately 3 µm height. Arranging formula: 4', 4a, 7", 7c, 6'", 2"", as, ?FM, Is, ps.
Archeopyl apical, PR+2'+3'. Operculum secat, foederate, (PR+2'+3'). Archeopyl shape rounded with a thickened margin.
Remarks: The emendation clarifies the arrangement of C. foveolatum and, for better comparability, describes the characteristics mentioned by McMinn using the terminology of Below. The wall structure is unfortunately not recognizable in the illustrations provided by McMinn. Here, it is assumed that it corresponds to the already known Cladopyxidium wall structure. The foveolate structure of the wall mentioned by McMinn has been observed in all species of Cladopyxidium in the present material. Only the distribution patterns differ. No evidence could be found for the formation of an archeopyl with the formula PR+1'+2'+3'+4'.
Specimens: 11
Statistics: Length: 24(31)36, Width: 21(28)32, Septal height: 4-5.
Measured specimens: 6.
Known range: Maastrichtian.
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. 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.
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Emendation Marheinecke, 1992 (p. 105) (translated from German):
Emended description: Cyst habit proximochorate, acavate, ovaloid to almost spheroidal, small to very small. Wall consisting of pedium and luxuria, which distally forms a tegillum. Tegillum scabrately pierced by irregularly distributed pores. The tegillum forms finite septa of approximately 3 µm height. Arranging formula: 4', 4a, 7", 7c, 6'", 2"", as, ?FM, Is, ps.
Archeopyl apical, PR+2'+3'. Operculum secat, foederate, (PR+2'+3'). Archeopyl shape rounded with a thickened margin.
Remarks: The emendation clarifies the arrangement of C. foveolatum and, for better comparability, describes the characteristics mentioned by McMinn using the terminology of Below. The wall structure is unfortunately not recognizable in the illustrations provided by McMinn. Here, it is assumed that it corresponds to the already known Cladopyxidium wall structure. The foveolate structure of the wall mentioned by McMinn has been observed in all species of Cladopyxidium in the present material. Only the distribution patterns differ. No evidence could be found for the formation of an archeopyl with the formula PR+1'+2'+3'+4'.
Specimens: 11
Statistics: Length: 24(31)36, Width: 21(28)32, Septal height: 4-5.
Measured specimens: 6.
Known range: Maastrichtian.