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Palaeoperidinium cretaceum
Palaeoperidinium cretaceum, (Pocock, 1962, p. 80, pl.14, figs.219–221 ex Davey, 1970, p.359), Lentin and Williams, 1976, p. 110; Emendations as Palaeoperidinium cretaceum: Harding, 1990a, p. 44; Evitt et al., 1998, p. 50
Originally Palaeoperidinium (name not validly published), subsequently Astrocysta, thirdly Lejeunia? (combination illegitimate), fourthly Subtilisphaera, fifthly (and now) Palaeoperidinium.
Taxonomic junior synonyms: Lejeunia (as Palaeoperidinium) ampla, according to Harker and Sarjeant in Harker et al. (1990, p.128); Astrocysta (as Palaeoperidinium) manumcooksonii, according to Lentin and Williams (1976, p.110).
The name Palaeoperidinium cretaceum was not validly published in Pocock (1962) since the generic name Palaeoperidinium was not validly published until 1967. Davey (1970, p.359), while validating the name as Astrocysta cretacea, proposed an "emendation".
Holotype: Pocock, 1962, pl.14, fig.219.
Age: Aptian–Albian.
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Original description: [Pocock 1962, p. 80]:
Diagnosis:
Theca longer than it is broad, ellipsoidal; epitheca long, conical tapering to a point and may or may not be surmounted by a solid apical horn; equatorial girdle well developed, helicoid; hypotheca more or less dome shaped, terminated by two hypothecal spines, one always being longer than the other. Thecal wall thin and transparent, pale yellow or colourless, with no visible system of plates; theca is either scabrate or finely granulose and, in well preserved specimens, usually contains yellow green rounded crystalline bodies; spherical cysts have been observed with the thecae of some specimens.
Dimensions:
Range: Length: 81-95 µm; breadth: 50-69 µm; Length of longer hypothecal spine: 12-25 µm; Length of shorter hypothecal spine: 4-10 µm.
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Emended description as Astrocysta cretacea:
Davey, 1970, p.359-360:
Diagnosis:
Shell pentagonal; epitract triangular, with broadly conical apical horn; hypotract bearing two conical antapical horns of unequal length. Outer membranes thin, enclosing inner body of similar shape. Cingulum marked by low ridges. Weak tabulation sometimes developed, marked by low thickenings of periphragm.
Outline of anterior intercalary plate 2a usually present, but in plate typically in place.
Dimensions:
Range: Overall length: 86-118 µm; Overall width: 57-82 µm. Number of specimens measured: 8.
Emended description: Davey, 1970, p.360: Astrocysta cretacea
The apical and two antapical horns are well developed, the latter differing in size from one another. The outer membrane is extremely thin, wrinkled and often possess slight thickenings which occasionally bear small pointed spines. These thickenings partially outline a tabulation which resembles the Peridinium-type tabulation described by Manum (1963). The cingulum is bordered by two low ridges and is only slightly laevo-rotatory. An archaeopyle has never been observed but the outline of paraplate 2a is usually present.
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Supplemental description: Brideaux, 1971, p.86: Lejeunia cretacea
Dinoflagellate cyst; outline pentagonal or rounded-pentagonal; apex tapering to a rounded or slightly pointed, short apical prominence; antapex with two antapical horns, the left antapical horn generally slightly or distinctly longer. Epitract slightly longer or nearly equal in length to the hypotract; hypotract tapel-ing slightly towards the antapex, flattened between antapical horns. Cyst wall thin; occasional specimens suggest a two-layered wall with the inner layer very closely appressed to the outer layer; no specimens have shown a definite separation into capsule and outer wall layer as in cavate dinoflagellate forms. Tabulation pattern not developed; occasional specimens bear incomplete traces of a possible tabulation pattern, expressed as faint lines on the cyst wall; these are generally overshadowed by a proliferation of such traces in completely random patterns. Cingulum present, often indistinct, outlined by narrow folds or low ridges; sulcus not noted. No distinct evidence of archeopyle structure noted; some specimens show and incomplete outline suggestive of an intercalary plate, but no rupture has been observed in thousands of specimens; some specimens have the apical portion broken off or show an incomplete rupture along the cingulum; these specimens appear to be exhibiting mechanical breakage rather than archeopyle formation,
Dimensions: On 42 measured specimens: length, 63-119 µm; width, 41-88 µm; apical horn length, 5-18 µm; length of left antapical horn, 12-29 µm; length of right antapical horn, 3-17 µm. A total of 90 specimens recorded, many more observed.
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Supplemental description: Jansonius, 1986, p.214
(Holotype) 70 x 104 µm overall, ventral aspect; total thickness of compressed specimen in center less than 1 µm; wall slightly uneven with wrinkles or granulation, ca 0.5 µm thick. Archeopyle is a transapical split; apical horn split along periphery, the shorter dorsal part offset from the longer ventral part which ends with a small piece of thickened wall material. The boundary of 3a, projecting noticeably at 10 o"clock on the margin of the epicyst, apparently is marked by a thin crest of 1.5 µm height, which appears to continue to the cingulum (possibly the margin of 5"?). Cingulum barely spiralling, delineated by low, thin ridges. Anterior margin of 2a marked by a low ridge, but this paraplate is not clearly delineated towards the cingulum (trapezoidal?, hexagonal?). A fine denticulation or scalloping of the margin outlining the antapical horns of the hypocyst, fades away towards the cingulum.
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Emended diagnosis: Harding 1990, p. 44-45
Shape. Typically pentagonal peridinioid ambitus. Prominent broad-based apical horn, two antapical horns of which the left-hand is the more pronounced. Epicyst usually longer than hypocyst. Greatest width across cingulum. Strong primary dorso-ventral compression.
Phragma: Autophragm, very thin ( ~0.2 µm thick), when well preserved shows corrugated intercalary bands delineating tabulation. Septa developed bordering cingulum, sulcus, ventral apical region. Plate areas have subdued reticulate sculpture.
Tabulation: Ortho-hexa peridinioid type, 4", 3a, 7"", Sc, 5"", 4s. Iso-deltaform second anterior intercalary. Apical structure indicates an apical pore plate and a small ventral canal plate. A cingular/sulcal transitional plate also present.
Archaeopyle.:Type (A313P), hemiepicystal, operculum often remains adherent along the cingulum.
Cingulum: Planar, with five plates and one transitional. Bordered by distally denticulate septa.
Sulcus: Consists of four plates; right sulcal plate bears a convex sulcal "list" which is prolonged onto the posterior sulcal in the form of a rostrum. Less prominent list" is found on the left sulcal.
Dimensions:
Length = (68) 80 ( 101 ) µm. Number of specimens measured = 30.
Remarks: Harding 1990, p. 44-45
The description of this species is revised following the examination of topotype material. Although the type species of the genus has been shown to be a fossil of extrathecal origin, P. cretaceum, is retained in the same genus. Bujak and Davies ( 1983) suggested that the genus Astrocysta Davey be retained for those species of Palaeoperidinium which were shown not to be extrathecal structures. This practice is unnecessary as there is an obvious phylogenetic relationship between the taxa. Such a practice would lead to the same problems of dual nomenclature presently experienced with modern motile dinoflagellates and their corresponding cyst stages. The morphotype described by Davey (1970) as the type of his new genus Astrocysta is not synonymized with P. cretaceum in this work. Unfortunately, the poor preservation of the Saskatchewan topotype specimens does not suit them to SEM analysis. but the resulting micrographs do show that the morphotype is a conventional intrathecal cyst and not an "exophragm" (Pl. 3, fig. 9). The morphology of the cyst does reveal that "Astrocysta" is a junior synonym of Palaeoperidinium (as envisaged above). Measurement of twenty-two specimens of A. cretacea has resulted in the following: length = (90) 112 5 (135) µm. The minimum and maximum dimensions comply with those given by Davey (1970). but the mean of Davey"s measurements is 10µm less than that determined here from a greater number of specimens. Thus, the average specimen from Davey"s material is a full 30µm (375%) longer than the average specimen of P. cretaceum. Whilst this could indicate an evolutionary increase in the size of the organism through Albian time, it is felt more likely that the morphotype described by Davey (1970) is referable to a separate taxon, albeit within the genus Palaeoperidinium. Judging from the associated palynoflora. "Astrocysta" cretacea appears to have occupied a more saline environment than P. cretaceum.
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Affinities:
Davey 1970, p.360: Astrocysta cretacea is rather similar to Lejeunia tricuspis O. Wetzel but the latter possesses a more pronounced cingulum.
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Originally Palaeoperidinium (name not validly published), subsequently Astrocysta, thirdly Lejeunia? (combination illegitimate), fourthly Subtilisphaera, fifthly (and now) Palaeoperidinium.
Taxonomic junior synonyms: Lejeunia (as Palaeoperidinium) ampla, according to Harker and Sarjeant in Harker et al. (1990, p.128); Astrocysta (as Palaeoperidinium) manumcooksonii, according to Lentin and Williams (1976, p.110).
The name Palaeoperidinium cretaceum was not validly published in Pocock (1962) since the generic name Palaeoperidinium was not validly published until 1967. Davey (1970, p.359), while validating the name as Astrocysta cretacea, proposed an "emendation".
Holotype: Pocock, 1962, pl.14, fig.219.
Age: Aptian–Albian.
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Original description: [Pocock 1962, p. 80]:
Diagnosis:
Theca longer than it is broad, ellipsoidal; epitheca long, conical tapering to a point and may or may not be surmounted by a solid apical horn; equatorial girdle well developed, helicoid; hypotheca more or less dome shaped, terminated by two hypothecal spines, one always being longer than the other. Thecal wall thin and transparent, pale yellow or colourless, with no visible system of plates; theca is either scabrate or finely granulose and, in well preserved specimens, usually contains yellow green rounded crystalline bodies; spherical cysts have been observed with the thecae of some specimens.
Dimensions:
Range: Length: 81-95 µm; breadth: 50-69 µm; Length of longer hypothecal spine: 12-25 µm; Length of shorter hypothecal spine: 4-10 µm.
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Emended description as Astrocysta cretacea:
Davey, 1970, p.359-360:
Diagnosis:
Shell pentagonal; epitract triangular, with broadly conical apical horn; hypotract bearing two conical antapical horns of unequal length. Outer membranes thin, enclosing inner body of similar shape. Cingulum marked by low ridges. Weak tabulation sometimes developed, marked by low thickenings of periphragm.
Outline of anterior intercalary plate 2a usually present, but in plate typically in place.
Dimensions:
Range: Overall length: 86-118 µm; Overall width: 57-82 µm. Number of specimens measured: 8.
Emended description: Davey, 1970, p.360: Astrocysta cretacea
The apical and two antapical horns are well developed, the latter differing in size from one another. The outer membrane is extremely thin, wrinkled and often possess slight thickenings which occasionally bear small pointed spines. These thickenings partially outline a tabulation which resembles the Peridinium-type tabulation described by Manum (1963). The cingulum is bordered by two low ridges and is only slightly laevo-rotatory. An archaeopyle has never been observed but the outline of paraplate 2a is usually present.
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Supplemental description: Brideaux, 1971, p.86: Lejeunia cretacea
Dinoflagellate cyst; outline pentagonal or rounded-pentagonal; apex tapering to a rounded or slightly pointed, short apical prominence; antapex with two antapical horns, the left antapical horn generally slightly or distinctly longer. Epitract slightly longer or nearly equal in length to the hypotract; hypotract tapel-ing slightly towards the antapex, flattened between antapical horns. Cyst wall thin; occasional specimens suggest a two-layered wall with the inner layer very closely appressed to the outer layer; no specimens have shown a definite separation into capsule and outer wall layer as in cavate dinoflagellate forms. Tabulation pattern not developed; occasional specimens bear incomplete traces of a possible tabulation pattern, expressed as faint lines on the cyst wall; these are generally overshadowed by a proliferation of such traces in completely random patterns. Cingulum present, often indistinct, outlined by narrow folds or low ridges; sulcus not noted. No distinct evidence of archeopyle structure noted; some specimens show and incomplete outline suggestive of an intercalary plate, but no rupture has been observed in thousands of specimens; some specimens have the apical portion broken off or show an incomplete rupture along the cingulum; these specimens appear to be exhibiting mechanical breakage rather than archeopyle formation,
Dimensions: On 42 measured specimens: length, 63-119 µm; width, 41-88 µm; apical horn length, 5-18 µm; length of left antapical horn, 12-29 µm; length of right antapical horn, 3-17 µm. A total of 90 specimens recorded, many more observed.
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Supplemental description: Jansonius, 1986, p.214
(Holotype) 70 x 104 µm overall, ventral aspect; total thickness of compressed specimen in center less than 1 µm; wall slightly uneven with wrinkles or granulation, ca 0.5 µm thick. Archeopyle is a transapical split; apical horn split along periphery, the shorter dorsal part offset from the longer ventral part which ends with a small piece of thickened wall material. The boundary of 3a, projecting noticeably at 10 o"clock on the margin of the epicyst, apparently is marked by a thin crest of 1.5 µm height, which appears to continue to the cingulum (possibly the margin of 5"?). Cingulum barely spiralling, delineated by low, thin ridges. Anterior margin of 2a marked by a low ridge, but this paraplate is not clearly delineated towards the cingulum (trapezoidal?, hexagonal?). A fine denticulation or scalloping of the margin outlining the antapical horns of the hypocyst, fades away towards the cingulum.
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Emended diagnosis: Harding 1990, p. 44-45
Shape. Typically pentagonal peridinioid ambitus. Prominent broad-based apical horn, two antapical horns of which the left-hand is the more pronounced. Epicyst usually longer than hypocyst. Greatest width across cingulum. Strong primary dorso-ventral compression.
Phragma: Autophragm, very thin ( ~0.2 µm thick), when well preserved shows corrugated intercalary bands delineating tabulation. Septa developed bordering cingulum, sulcus, ventral apical region. Plate areas have subdued reticulate sculpture.
Tabulation: Ortho-hexa peridinioid type, 4", 3a, 7"", Sc, 5"", 4s. Iso-deltaform second anterior intercalary. Apical structure indicates an apical pore plate and a small ventral canal plate. A cingular/sulcal transitional plate also present.
Archaeopyle.:Type (A313P), hemiepicystal, operculum often remains adherent along the cingulum.
Cingulum: Planar, with five plates and one transitional. Bordered by distally denticulate septa.
Sulcus: Consists of four plates; right sulcal plate bears a convex sulcal "list" which is prolonged onto the posterior sulcal in the form of a rostrum. Less prominent list" is found on the left sulcal.
Dimensions:
Length = (68) 80 ( 101 ) µm. Number of specimens measured = 30.
Remarks: Harding 1990, p. 44-45
The description of this species is revised following the examination of topotype material. Although the type species of the genus has been shown to be a fossil of extrathecal origin, P. cretaceum, is retained in the same genus. Bujak and Davies ( 1983) suggested that the genus Astrocysta Davey be retained for those species of Palaeoperidinium which were shown not to be extrathecal structures. This practice is unnecessary as there is an obvious phylogenetic relationship between the taxa. Such a practice would lead to the same problems of dual nomenclature presently experienced with modern motile dinoflagellates and their corresponding cyst stages. The morphotype described by Davey (1970) as the type of his new genus Astrocysta is not synonymized with P. cretaceum in this work. Unfortunately, the poor preservation of the Saskatchewan topotype specimens does not suit them to SEM analysis. but the resulting micrographs do show that the morphotype is a conventional intrathecal cyst and not an "exophragm" (Pl. 3, fig. 9). The morphology of the cyst does reveal that "Astrocysta" is a junior synonym of Palaeoperidinium (as envisaged above). Measurement of twenty-two specimens of A. cretacea has resulted in the following: length = (90) 112 5 (135) µm. The minimum and maximum dimensions comply with those given by Davey (1970). but the mean of Davey"s measurements is 10µm less than that determined here from a greater number of specimens. Thus, the average specimen from Davey"s material is a full 30µm (375%) longer than the average specimen of P. cretaceum. Whilst this could indicate an evolutionary increase in the size of the organism through Albian time, it is felt more likely that the morphotype described by Davey (1970) is referable to a separate taxon, albeit within the genus Palaeoperidinium. Judging from the associated palynoflora. "Astrocysta" cretacea appears to have occupied a more saline environment than P. cretaceum.
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Affinities:
Davey 1970, p.360: Astrocysta cretacea is rather similar to Lejeunia tricuspis O. Wetzel but the latter possesses a more pronounced cingulum.
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