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Chytroeisphaeridia baetica
Chyrtoeisphaeridia baetica, Riegel, 1974; emend. Riegel and Sarjeant, 1982
This species was questionably retained in Chytroeisphaeridia by Davey, 1979. Riegel and Sarjeant, 1982, included the species in Chytroeisphaeridia without question.
Holotype: Riegel, 1974, pl.1, fig.2
Locus typicus: Puerto de Bolonia, Province of Cadiz, Spain
Stratum typicum: ?Senonian
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Original description: [Riegel, 1974, p.349-353]:
Diagnosis:
Outline of shell subcircular to ovoid, width consistently greater than length.
Archeopyle apical with angular margin. Operculum more or less six-sided, attached.
Shell wall thin and simple, surface finely pitted. Archeopyle diameter exceeding 2/3 of maximum shell diameter.
Description:
Collapsed cysts show numerous large compression folds indicating that they were greatly inflated or nearly spherical in shape originally. The broadly rounded apex is often skewed to one side. A few specimens show a slight indentation at the base. The ratio of length without operculum to width varies between 3:5 and 1:1.
The archeopyle margin varies from being almost straight to clearly angular usually showing a shallow sulcal notch. Slits are lacking except for occasional occurrences at the sulcal notch. The operculum appears more or less six-sided with slightly reentrant angles near the sulcal hinge. It is normally attached but torn off in about 1/3 of the specimens observed.
The wall of the shell is usually less than 1 µm in thickness. In transmitted light its surface appears slightly roughened. Scanning electron micrographs show the surface to be finely and irregularly pitted (pl.1, fig.4). In some specimens a small knob has been observed near the antapex perhaps indicating the place of attachment of the cyst to the theca.
Dimensions:
Range of length without operculum: 42-72 µm. Range of width: 57-75 µm. Measurements have been taken from 15 specimens showing least distortion by compression.
Affinities: (p.353-354):
Ch. beetica is closely similar to Ch. chytroeides (Sarjeant 1962). Differences between the two involve size range, ratio of archeopyle diameter to shell width and nature of shell surface. The observed size range of Ch. baetica comprises only the larger portion of the ranges given for Ch. chytroeides (Gitmez and Sarjeant 1972). Smaller forms are conspicuously lacking. In all specimens the ratio of archeopyle diameter to shell width is more than 2/3 and thus greater than that in Ch. chylroeides. The shell surface of Ch. baetica is finely and irregularly pitted to various degrees, but never really smooth. An antapical knob has never been mentioned for Ch. chytroeides.
Ch. baetica differs from Ch. euteiches Davey 969 by its thin shell wall and from Ch. pococki Sarjeant 1968 by the lack of a pronounced granulation. It appears to be rather similar to Forma N of Evitt (1967, pl.1, fig.17) from the Lower Cretaceous of California, but is proportionately greater in width.
The differences between Ch. baetica and Ch. cilytroeides are admittedly slight and it might be difficult to distinguish the two if they occurred in the same sample. But considering the paucity of morphological characteristics in the genus Chytroeisphaeridia apparently minor details have to be used in defining species. In view of the wide gap between the known stratigraphic range of Ch. chytroeides (Callovian to Kimmeridgian) and the age of the above described forms (Upper Cretaceous) it seems expedient to keep the two populations taxonomically separate if at all possible. Clues to reworking of older forms have not been observed.
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Emended description:
Riegel and Sarjeant, 1982, p. 300:
Diagnosis:
Cyst sphaeroidal to broadly ovoidal, with a single knob-like protrusion at the antapex in some specimens but otherwise without horns, processes or other major surficial ornamentation.
Phragma usually less than 1 µm in thickness, apparently composed of a single layer (autophragm) only. In transmitted light its surface appears slightly roughened; scanning electron micrographs show it to be finely and irregularly pitted.
Archaeopyle single-plate precingular, very large and roughly hexagonal; operculum attached at its antapical margin or free.
Dimensions:
Holotype: length 57 µm, breadth 60 µm.
Figured specimens: (2a) length 70 µm, breadth 58 µm; (2b) length 78 µm, breadth 71 µm; (2c) length 68 µm, breadth 50 µm; (2d) length 70 µm, breadth 60 µm; (herein) length 72 µm, breadth 65 µm.
Range of dimensions: length 57-78 µm, breadth 42-72 µm.
Discussion:
In his review of the genus Chytroeisphaeridia, following his demonstration that its type species develops a precingular (and not an apical) archaeopyle, Davey (1979) discussed this species and concluded (p. 217) that "The exact nature of the archaeopyle remains unclear and may not be resolved until a detached operculum is identified." Our reexamination of the type material indicated that the archaeopyle was a very large precingular one, formed presumably by the loss of a large paraplate 3"; this was confirmed when a specimen hitherto not illustrated was examined, in which the shape of the operculum was shown particularly well (see Fig. 8D). This species is thus correctly attributed to the genus in its new acceptation.
Compression of specimens that have lost the operculum gives an impression of very great breadth; the size of the operculum, in proportion to the cyst cross-measurement, indeed appears larger than in the type species Chytroeisphaeridia (Sarjeant, 1962). Another distinguishing feature is the surface pitting; the surface of C. chytroeides appears smooth in transmitted light.
This species was questionably retained in Chytroeisphaeridia by Davey, 1979. Riegel and Sarjeant, 1982, included the species in Chytroeisphaeridia without question.
Holotype: Riegel, 1974, pl.1, fig.2
Locus typicus: Puerto de Bolonia, Province of Cadiz, Spain
Stratum typicum: ?Senonian
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Riegel, 1974, p.349-353]:
Diagnosis:
Outline of shell subcircular to ovoid, width consistently greater than length.
Archeopyle apical with angular margin. Operculum more or less six-sided, attached.
Shell wall thin and simple, surface finely pitted. Archeopyle diameter exceeding 2/3 of maximum shell diameter.
Description:
Collapsed cysts show numerous large compression folds indicating that they were greatly inflated or nearly spherical in shape originally. The broadly rounded apex is often skewed to one side. A few specimens show a slight indentation at the base. The ratio of length without operculum to width varies between 3:5 and 1:1.
The archeopyle margin varies from being almost straight to clearly angular usually showing a shallow sulcal notch. Slits are lacking except for occasional occurrences at the sulcal notch. The operculum appears more or less six-sided with slightly reentrant angles near the sulcal hinge. It is normally attached but torn off in about 1/3 of the specimens observed.
The wall of the shell is usually less than 1 µm in thickness. In transmitted light its surface appears slightly roughened. Scanning electron micrographs show the surface to be finely and irregularly pitted (pl.1, fig.4). In some specimens a small knob has been observed near the antapex perhaps indicating the place of attachment of the cyst to the theca.
Dimensions:
Range of length without operculum: 42-72 µm. Range of width: 57-75 µm. Measurements have been taken from 15 specimens showing least distortion by compression.
Affinities: (p.353-354):
Ch. beetica is closely similar to Ch. chytroeides (Sarjeant 1962). Differences between the two involve size range, ratio of archeopyle diameter to shell width and nature of shell surface. The observed size range of Ch. baetica comprises only the larger portion of the ranges given for Ch. chytroeides (Gitmez and Sarjeant 1972). Smaller forms are conspicuously lacking. In all specimens the ratio of archeopyle diameter to shell width is more than 2/3 and thus greater than that in Ch. chylroeides. The shell surface of Ch. baetica is finely and irregularly pitted to various degrees, but never really smooth. An antapical knob has never been mentioned for Ch. chytroeides.
Ch. baetica differs from Ch. euteiches Davey 969 by its thin shell wall and from Ch. pococki Sarjeant 1968 by the lack of a pronounced granulation. It appears to be rather similar to Forma N of Evitt (1967, pl.1, fig.17) from the Lower Cretaceous of California, but is proportionately greater in width.
The differences between Ch. baetica and Ch. cilytroeides are admittedly slight and it might be difficult to distinguish the two if they occurred in the same sample. But considering the paucity of morphological characteristics in the genus Chytroeisphaeridia apparently minor details have to be used in defining species. In view of the wide gap between the known stratigraphic range of Ch. chytroeides (Callovian to Kimmeridgian) and the age of the above described forms (Upper Cretaceous) it seems expedient to keep the two populations taxonomically separate if at all possible. Clues to reworking of older forms have not been observed.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Emended description:
Riegel and Sarjeant, 1982, p. 300:
Diagnosis:
Cyst sphaeroidal to broadly ovoidal, with a single knob-like protrusion at the antapex in some specimens but otherwise without horns, processes or other major surficial ornamentation.
Phragma usually less than 1 µm in thickness, apparently composed of a single layer (autophragm) only. In transmitted light its surface appears slightly roughened; scanning electron micrographs show it to be finely and irregularly pitted.
Archaeopyle single-plate precingular, very large and roughly hexagonal; operculum attached at its antapical margin or free.
Dimensions:
Holotype: length 57 µm, breadth 60 µm.
Figured specimens: (2a) length 70 µm, breadth 58 µm; (2b) length 78 µm, breadth 71 µm; (2c) length 68 µm, breadth 50 µm; (2d) length 70 µm, breadth 60 µm; (herein) length 72 µm, breadth 65 µm.
Range of dimensions: length 57-78 µm, breadth 42-72 µm.
Discussion:
In his review of the genus Chytroeisphaeridia, following his demonstration that its type species develops a precingular (and not an apical) archaeopyle, Davey (1979) discussed this species and concluded (p. 217) that "The exact nature of the archaeopyle remains unclear and may not be resolved until a detached operculum is identified." Our reexamination of the type material indicated that the archaeopyle was a very large precingular one, formed presumably by the loss of a large paraplate 3"; this was confirmed when a specimen hitherto not illustrated was examined, in which the shape of the operculum was shown particularly well (see Fig. 8D). This species is thus correctly attributed to the genus in its new acceptation.
Compression of specimens that have lost the operculum gives an impression of very great breadth; the size of the operculum, in proportion to the cyst cross-measurement, indeed appears larger than in the type species Chytroeisphaeridia (Sarjeant, 1962). Another distinguishing feature is the surface pitting; the surface of C. chytroeides appears smooth in transmitted light.