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Cooksonidium
From Fensome et al., 2019:
Cooksonidium, Stover and Williams, 1995, p.106–107.
Type: Cookson and Eisenack, 1965a, pl.15, fig.7, as Cordosphaeridium capricornum.
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Original description: [Stover and Williams, 1995]:
Synopsis:
Cysts skolochorate, central body subspherical and bears 16 to 18 intratabular processes and process complexes; process stems solid, smooth to fibroid, tips expanded distally, arcuate or rarely licrate or heart-shaped, ends free or connected by trabeculae; epicyst with 10 or 11 processes, hypocyst with six or seven processes arranged in the standard sexiform pattern, paracingular processes absent; archeopyle apical, operculum tetratabular, simple and free.
Description:
Shape: Cysts skolochorate, central body subspherical.
Wall relationships: Autophragm only.
Wall features: Autophragm ornamented with features of low relief; intratabular processes usually with single stems, occasionally with branched stems; most process complexes arcuate with 2 to 4 stems; stems solid, smooth to fibroid; tips expanded, arcuate, less commonly licrate; antapical process complex usually heart-shaped with distal ring trabecula.
Excystment mode: Archeopyle apical, operculum tetratabular, simple and free.
Paratabulation: Gonyaulacoid, paratabulation indicated on epicyst by archeopyle sutures and locations of intratabular structures, elsewhere on cyst by positions of intratabular features only. Process formula: 4`, 6``, 0c, 5```, 0-1p, 1````, 0-las; paracingular processes typically absent and first precingular paraplate narrower than sixth; hypocystal configuration standard sexiform.
Paracingulum: Indicated by absence of processes.
Parasulcus: Anterior position reflected by a more or less medial sulcal notch; an anterior sulcal process may be present.
Size: Intermediate to large; diameter including processes 75 µm to 110 µm.
Affinities:
Cooksonidium is characterized by having a subspherical body bearing both simple intratabular processes and intratabular or penitabular process complexes (pl. 7, fig. 6), by the general absence of paracingular processes (pl. 7, fig. 4) and by having the hypocystal processes arranged in the standard sexiform pattern (pl. 7, fig. 6). In addition, the first precingular paraplate is narrower than the sixth and the antapical process complex is generally heart-shaped with a distal ring trabecula (pl. 7, fig. 7). Emmetrocysta Stover 1975 has mostly or exclusively intratabular process complexes whose distal ends are connected by ring trabeculae and the ventral processes may be interconnected by trabeculae. Also, Emmetrocysta has up to three parasulcal processes, including a posterior sulcal process that is always present. Areosphaeridium Eaton 1971 emended has solid intratabular processes with vasiform to clypeate tips, may have paracingular processes and does not possess an anterior parasulcal process. In addition, the posterior polar area on Areosphaeridium has a single intratabular process rather than a cardioform process complex (pl. 1, figs. 6a-c).
Cooksonidium, Stover and Williams, 1995, p.106–107.
Type: Cookson and Eisenack, 1965a, pl.15, fig.7, as Cordosphaeridium capricornum.
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Original description: [Stover and Williams, 1995]:
Synopsis:
Cysts skolochorate, central body subspherical and bears 16 to 18 intratabular processes and process complexes; process stems solid, smooth to fibroid, tips expanded distally, arcuate or rarely licrate or heart-shaped, ends free or connected by trabeculae; epicyst with 10 or 11 processes, hypocyst with six or seven processes arranged in the standard sexiform pattern, paracingular processes absent; archeopyle apical, operculum tetratabular, simple and free.
Description:
Shape: Cysts skolochorate, central body subspherical.
Wall relationships: Autophragm only.
Wall features: Autophragm ornamented with features of low relief; intratabular processes usually with single stems, occasionally with branched stems; most process complexes arcuate with 2 to 4 stems; stems solid, smooth to fibroid; tips expanded, arcuate, less commonly licrate; antapical process complex usually heart-shaped with distal ring trabecula.
Excystment mode: Archeopyle apical, operculum tetratabular, simple and free.
Paratabulation: Gonyaulacoid, paratabulation indicated on epicyst by archeopyle sutures and locations of intratabular structures, elsewhere on cyst by positions of intratabular features only. Process formula: 4`, 6``, 0c, 5```, 0-1p, 1````, 0-las; paracingular processes typically absent and first precingular paraplate narrower than sixth; hypocystal configuration standard sexiform.
Paracingulum: Indicated by absence of processes.
Parasulcus: Anterior position reflected by a more or less medial sulcal notch; an anterior sulcal process may be present.
Size: Intermediate to large; diameter including processes 75 µm to 110 µm.
Affinities:
Cooksonidium is characterized by having a subspherical body bearing both simple intratabular processes and intratabular or penitabular process complexes (pl. 7, fig. 6), by the general absence of paracingular processes (pl. 7, fig. 4) and by having the hypocystal processes arranged in the standard sexiform pattern (pl. 7, fig. 6). In addition, the first precingular paraplate is narrower than the sixth and the antapical process complex is generally heart-shaped with a distal ring trabecula (pl. 7, fig. 7). Emmetrocysta Stover 1975 has mostly or exclusively intratabular process complexes whose distal ends are connected by ring trabeculae and the ventral processes may be interconnected by trabeculae. Also, Emmetrocysta has up to three parasulcal processes, including a posterior sulcal process that is always present. Areosphaeridium Eaton 1971 emended has solid intratabular processes with vasiform to clypeate tips, may have paracingular processes and does not possess an anterior parasulcal process. In addition, the posterior polar area on Areosphaeridium has a single intratabular process rather than a cardioform process complex (pl. 1, figs. 6a-c).