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Yolkinigymnium expansum
Yolkinigymnium expansum, Firth, 1993, p.201
Holotype: Firth, 1993, pl.5, figs.6-7
Locus typicus: Ripley Formation, from the USGS Albany Core from Albany, Georgia. Depth in core: 321.8 m.
Stratum typicum: Early Maastrichtian
Original description: Firth, 1993:
Cyst extremely elongate, with epitract length ranging from about 1/12 to 1/6 of the total length of cyst. Hypotract slightly wider across the paracingulum than epitract. Apex terminates in a rounded point; antapex digitate. Autophragm smooth to faintly granular, faintly striated, with costae on both epi- and hypotract. Paracingulum narrow, laevorotatory, displaced about one cingulum width. On expanded specimens, a shallow parasulcus can be located by irregularly shaped flagellar scar on ventral surface. Parasulcus extends slightly onto epitract, and approximately 1/3 the distance along hypotract. No archeopyle observed.
Dimensions:
Cyst body length: 213.0-435.0 µm (mean 313.7 µm). Cyst body width: 31.0 µm, n= 2). Epicyst length: 33.0-36.0 µm (mean 34.7 µm). Hypocyst length: 180.0 399.0 µm (mean 279.0 µm). Cingulum width: 6.0-7.0 µm (mean 6.7 µm). Approximate wall thickness: 0.5-0.7 µm. Cingulum Index: 8.3-15.5 (mean 11.9). Total number of specimens measured= 3.
Affinities/Comparison:
Yolkinigymnium expansum differs from Yolkinigymnium lanceolatum in that it has numerous costae in the autophragm which enables the cyst to expand or contract, whereas the latter species does not have costae in the autophragm. The specimens illustrated as Dinogymnium sp. A and sp. B by May (1980, pp. 42-43, pl. 11, figs. 17 18) are examples of specimens of Y. expansum with greatly expanded hypotracts.
Holotype: Firth, 1993, pl.5, figs.6-7
Locus typicus: Ripley Formation, from the USGS Albany Core from Albany, Georgia. Depth in core: 321.8 m.
Stratum typicum: Early Maastrichtian
Original description: Firth, 1993:
Cyst extremely elongate, with epitract length ranging from about 1/12 to 1/6 of the total length of cyst. Hypotract slightly wider across the paracingulum than epitract. Apex terminates in a rounded point; antapex digitate. Autophragm smooth to faintly granular, faintly striated, with costae on both epi- and hypotract. Paracingulum narrow, laevorotatory, displaced about one cingulum width. On expanded specimens, a shallow parasulcus can be located by irregularly shaped flagellar scar on ventral surface. Parasulcus extends slightly onto epitract, and approximately 1/3 the distance along hypotract. No archeopyle observed.
Dimensions:
Cyst body length: 213.0-435.0 µm (mean 313.7 µm). Cyst body width: 31.0 µm, n= 2). Epicyst length: 33.0-36.0 µm (mean 34.7 µm). Hypocyst length: 180.0 399.0 µm (mean 279.0 µm). Cingulum width: 6.0-7.0 µm (mean 6.7 µm). Approximate wall thickness: 0.5-0.7 µm. Cingulum Index: 8.3-15.5 (mean 11.9). Total number of specimens measured= 3.
Affinities/Comparison:
Yolkinigymnium expansum differs from Yolkinigymnium lanceolatum in that it has numerous costae in the autophragm which enables the cyst to expand or contract, whereas the latter species does not have costae in the autophragm. The specimens illustrated as Dinogymnium sp. A and sp. B by May (1980, pp. 42-43, pl. 11, figs. 17 18) are examples of specimens of Y. expansum with greatly expanded hypotracts.