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Chytroeisphaeridia chytroeides
Chytroeisphaeridia chytroeides, (Sarjeant, 1962), Downie and Sarjeant, 1965; emend. Davey, 1979
Holotype: Sarjeant 1962, pl.70, fig.13
Locus typicus: Melton, S Yorkshire, England
Stratum typicum: Oxfordian
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Original description as Leiosphaeridia (Chytroisphaeridia) chytroeides: [Sarjeant, 1962, p. 493-494]:
Diagnosis:
A species of Leiosphaeridia having a smooth or faintly granular shell of spherical to broadly ovoidal shape and variable thickness. A large pylome of polygonal outline, without a thickened rim, is characteristic.
Dimensions:
Holotype: Diameter (maximum) 50 µm.
Range of dimensions: Maximum diameters 30-60 µm.
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Emended description:
Davey, 1979, p. 211-212:
Diagnosis:
The cysts were originally spheroidal in shape and are composed of an apparently single-layered wall (autophragm) of moderate thickness (0.5-1 µm). The wall is smooth externally, unstructured and of constant thickness. Apical, antapical and lateral structures are absent.
A simple precingular archaeopyle is typically developed formed by the loss of one paraplate (presumably 3''); the operculum often occurs within the cyst. The apical side of the operculum, and the archaeopyle, may be irregularly torn or regularly notched.
Description:
C. chytroides, being originally approximately spherical, is always flattened and folded to some extent during preservation; since it has a moderately stout wall, this deformation typically takes the form of one or two arcuate folds. Very few specimens are preserved in dorso-ventral orientation which strongly suggests that there is no cyst flattening in this plane.
In fact the majority of cysts are preserved so that the archaeopyle occupies a marginal position, the cysts being either flattened laterally or, more rarely, apically-antapically. The operculum has a tapering hexagonal shape which is typical of the dorsal precingular paraplates and usually occurs within the cyst (p. 210); these points are well illustrated by Bjaerke 1977 (Plate 7, fig. 5).
Dimensions:
Holotype diameter 50 µm, diameter of type material 30-6 µm. Maximum diameters in present topotype material 37(45)54 µm. 10 specimens measured.
Affinities:
The most similarly described species is Tapeinosphaeridium pericompsum loannides et. al. 1977 which is transferred to Chytroeisphaeridia. This mid-Kimmeridgian species is differentiated from C. chytroeides by having a thinner, and consequently, more folded wall.
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Notes:
G.L. Williams short notes on species, Mesozoic-Cenozoic dinocyst course, Urbino, Italy, May 17-22, 1999 - LPP VIEWER CD-ROM 99.5.
Chytroeisphaeridia chytroeides (Sarjeant, 1962a) Downie and Sarjeant, 1965, is spheroidal with a single layered wall 0.5-1 µm thick. The wall is smooth. There are no protuberences. Maximum diameters 30-60 µm.
Holotype: Sarjeant 1962, pl.70, fig.13
Locus typicus: Melton, S Yorkshire, England
Stratum typicum: Oxfordian
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description as Leiosphaeridia (Chytroisphaeridia) chytroeides: [Sarjeant, 1962, p. 493-494]:
Diagnosis:
A species of Leiosphaeridia having a smooth or faintly granular shell of spherical to broadly ovoidal shape and variable thickness. A large pylome of polygonal outline, without a thickened rim, is characteristic.
Dimensions:
Holotype: Diameter (maximum) 50 µm.
Range of dimensions: Maximum diameters 30-60 µm.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Emended description:
Davey, 1979, p. 211-212:
Diagnosis:
The cysts were originally spheroidal in shape and are composed of an apparently single-layered wall (autophragm) of moderate thickness (0.5-1 µm). The wall is smooth externally, unstructured and of constant thickness. Apical, antapical and lateral structures are absent.
A simple precingular archaeopyle is typically developed formed by the loss of one paraplate (presumably 3''); the operculum often occurs within the cyst. The apical side of the operculum, and the archaeopyle, may be irregularly torn or regularly notched.
Description:
C. chytroides, being originally approximately spherical, is always flattened and folded to some extent during preservation; since it has a moderately stout wall, this deformation typically takes the form of one or two arcuate folds. Very few specimens are preserved in dorso-ventral orientation which strongly suggests that there is no cyst flattening in this plane.
In fact the majority of cysts are preserved so that the archaeopyle occupies a marginal position, the cysts being either flattened laterally or, more rarely, apically-antapically. The operculum has a tapering hexagonal shape which is typical of the dorsal precingular paraplates and usually occurs within the cyst (p. 210); these points are well illustrated by Bjaerke 1977 (Plate 7, fig. 5).
Dimensions:
Holotype diameter 50 µm, diameter of type material 30-6 µm. Maximum diameters in present topotype material 37(45)54 µm. 10 specimens measured.
Affinities:
The most similarly described species is Tapeinosphaeridium pericompsum loannides et. al. 1977 which is transferred to Chytroeisphaeridia. This mid-Kimmeridgian species is differentiated from C. chytroeides by having a thinner, and consequently, more folded wall.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Notes:
G.L. Williams short notes on species, Mesozoic-Cenozoic dinocyst course, Urbino, Italy, May 17-22, 1999 - LPP VIEWER CD-ROM 99.5.
Chytroeisphaeridia chytroeides (Sarjeant, 1962a) Downie and Sarjeant, 1965, is spheroidal with a single layered wall 0.5-1 µm thick. The wall is smooth. There are no protuberences. Maximum diameters 30-60 µm.