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Cygnusicysta
From Williams et al., 2017:
[Cygnusicysta, Riding and Helby, 2001e, p. 112-114.
Type species: Cygnusicysta taltarniana, Riding and Helby, 2001e (fig.1L)]
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Original description: [Riding and Helby, 2001e]:
Diagnosis:
Proximate, circumcavate dinoflagellate cysts, small to intermediate in size and compressed subspherical in shape.
Periphragm and endophragm smooth or having low relief ornamentation. Indications of paratabulation lacking apart from the principal and accessory archaeopyle sutures.
Paratabulation apparently gonyaulacalean. Paracingulum not indicated, parasulcus indicated by parasulcal notch.
Archaeopyle apical, operculum free, simple.
Remarks:
The principal archaeopyle suture of the type, Cygnusicysta taltarniana, is angular and indicates the presence of six precingular paraplates, sometimes marked by short accessory archaeopyle sutures. Furthermore, isolated opercula of the type indicate that four apical paraplates are present. Cygnusicysta taltarniana was regarded as an acritarch until the archaeopyle was recognized.
Affinities:
This new genus is similar to Leberidocysta Stover & Evitt 1978 in that both are cavate and have apical archaeopyles. However, the endocyst of the genotype, Leberidocysta chlamydata (Cookson and Eisencak 1962) Stover & Evitt 1978, is characteristically elongate ellipsoidal in outline and verrucate. Furthermore, the pericysts is irregular in outline due to intense folding and damage of the periphragm. In some cases, the periphragm may be entirely lost (Cookson & Eisenack, 1962a, p. 496) The pericoel of Cygnusicysta, by contrast, is relatively narrow and the periphragm is not generally prone to mechanical damage, apart from folding. It appears that a restudy of species currently assigned to Leberidocysta is needed.
[Cygnusicysta, Riding and Helby, 2001e, p. 112-114.
Type species: Cygnusicysta taltarniana, Riding and Helby, 2001e (fig.1L)]
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Original description: [Riding and Helby, 2001e]:
Diagnosis:
Proximate, circumcavate dinoflagellate cysts, small to intermediate in size and compressed subspherical in shape.
Periphragm and endophragm smooth or having low relief ornamentation. Indications of paratabulation lacking apart from the principal and accessory archaeopyle sutures.
Paratabulation apparently gonyaulacalean. Paracingulum not indicated, parasulcus indicated by parasulcal notch.
Archaeopyle apical, operculum free, simple.
Remarks:
The principal archaeopyle suture of the type, Cygnusicysta taltarniana, is angular and indicates the presence of six precingular paraplates, sometimes marked by short accessory archaeopyle sutures. Furthermore, isolated opercula of the type indicate that four apical paraplates are present. Cygnusicysta taltarniana was regarded as an acritarch until the archaeopyle was recognized.
Affinities:
This new genus is similar to Leberidocysta Stover & Evitt 1978 in that both are cavate and have apical archaeopyles. However, the endocyst of the genotype, Leberidocysta chlamydata (Cookson and Eisencak 1962) Stover & Evitt 1978, is characteristically elongate ellipsoidal in outline and verrucate. Furthermore, the pericysts is irregular in outline due to intense folding and damage of the periphragm. In some cases, the periphragm may be entirely lost (Cookson & Eisenack, 1962a, p. 496) The pericoel of Cygnusicysta, by contrast, is relatively narrow and the periphragm is not generally prone to mechanical damage, apart from folding. It appears that a restudy of species currently assigned to Leberidocysta is needed.