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Cribroperidinium hadrum
From Fensome et al., 2019:
Cribroperidinium hadrum (Sarjeant, 1966b, p.119–121, pl.14, fig.1; text-fig.28) Duxbury, 2019, p.185. Emendation: Duxbury (2019, p.184), as Cribroperidinium. Holotype: Sarjeant, 1966b, pl.14, fig.1. Originally Gonyaulacysta, subsequently Millioudodinium, thirdly Rhynchodiniopsis, fourthly Leptodinium?, fifthly (and now) Cribroperidinium. Age: late Barremian.
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Original diagnosis: Sarjeant, 1966, p. 119: Gonyaulacysta hadra
A Gonyaulacysta with thick-walled, spherical to spheroidal shell and long, tapering apical horn. Tabulation 4', ?oa, 6'', 6c, 6''', 1p, 1p.v., 1''''; poorly marked by crests in form of very low ridges bearing well spaced, extremely abbreviate spinelets. Cingulum weakly spiral: sulcus short, confined to ventral region. Surface generally densely granular.
Dimensions: holotype: overall length 151 µm, breadth 117 µm. Shell length 117 µm; length of horn 34 µm; breadth of cingulum c.7 µm. Paratype: overall length 145 µm, breadth c.112 µm; shell length 105 µm; length of horn 40 µm; breadth of cingulum c.5 µm. Range: overall length c.140-155 µm.
Original description: Sarjeant, 1966, p. 120-121: Gonyaulacysta hadra
This is an unusually large and very characteristic species, quite frequent at this horizon, some 20 specimens having been studied. The dense granulation and relatively inconspicuous character of the crests render the tabulation difficult to determine: Text-fig. 28 was prepared from study of several specimens and is unlikely to be accurate in detail. On most specimens, including the holotype, granules are absent from various small patches of the surface: this appears to result from damage. Granulation is consistently faint or lacking on the sulcus, which is somewhat sunken.
The test is spherical to spheroidal and composed of two distinct layers; a fairly thin periphragm and a thicker endophragm. The endophragm bulges only into the base of the apical horn, so that the horn contains a cavity between the wall layers. Four apical plates are present, jointly forming the apical horn. Plate 1' is long and broad, occupying the anterior prolongation of the sulcus. An anterior inter-
calary plate could not be determined. Six precingular plates are present, plates 1'' and 6'' being reduced. There are also six postcingular plates, with plate 1''' reduced to accommodate the large posterior intercalary plate. A narrow posterior ventral plate separates the polygonal antapical plate from the sulcus.
The cingulum forms a feebly laevorotatory spiral, its two ends scarcely differing in antero-posterior position. The sulcus is short, extending only over the middle third of the ventral surface: it is widest at mid-point and tapers to anterior and posterior.
A precingular archaeopyle, formed by loss of plate 3'', is present in all specimens seen.
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Emended diagnosis Duxbury, 2019
Emended Diagnosis: A very large, ovoidal, proximate cyst with a prominent, tapering, blunt-ended apical horn approximately one quarter of the cyst length. Autophragm very thick and fibro-perforate, without surface ornament and forming a broad, rounded apical protuberance. A very thin outer membrane covers the cyst and bears low surface ridges outlining a tabulation typical for the genus. Some separation of wall layers can be particularly prominent around the cingulum and at the antapex; the longer, distal part of the apical horn appears to be constructed of this outer layer. Archeopyle large, single-plate precingular (3''), operculum free.
Remarks: The questionable transfer of this species to Leptodinium Klement 1960 by Helenes (1984, p. 131) is rejected here. His comment that “Sarjeant’s (in Davey et al. 1966) text-figure 28 suggests the presence of quadrate X and Z paraplates” is negated by Sarjeant’s comment (1966a, p. 120) that, “Text-figure 28 was prepared from study of several specimens and is unlikely to be accurate in detail”. In the present study, despite the common occurrence of this species, distortion of the low sutural ridges has also precluded detailed analysis of the tabulation. However, the general form and (where discernible) tabulation of this species allows its positive assignment to Cribroperidinium.
Cribroperidinium hadrum is characterised by its very large size, thick autophragm and lack of prominent surface ornament. The surface of other large species, including Cribroperidinium edwardsii (Cookson and Eisenack 1958) Davey 1969 tends to be covered with verrucae, short spines or tubercles which are often aligned. Fourteen specimens were measured here, with the following dimensions – length 162(138)104 μm x breadth 129(113)89 μm, very similar to those quoted by Sarjeant (1966a, p. 120).
This species is also characterised by what appears to be a thin, “loose-fitting”, finely-wrinkled outer membrane over which run very low ridges marking the tabulation. This membrane might generally be termed an ectophragm, as described by Evitt (1985, p. 65) although it is typically separate from the autophragm around the cingulum (suturocavation beneath each cingular ridge) and at the antapex. Also, the long apical horn appears to be mainly formed by this outer layer (Plate 8, Figures 1, 3, 5).
Divergence of wall layers in Cribroperidinium has been discussed above for C. cornutum, a species which also shows cingular and antapical wall separation; this feature is much more extreme in C. cornutum than in C. hadrum. Helenes’s (1984, p. 112) description of the wall structure of Cribroperidinium as autophragm which may be differentiated into a homogeneous and structureless inner part and a vesicular to “spongy looking” outer part, without separation of layers does not accurately describe C. hadrum or C. cornutum. It is the opposite particularly of what is seen in C. hadrum, which has a thick “spongy-looking” inner and a very thin outer layer as noted by Sarjeant (1966a, p. 120), who described “two distinct layers; a fairly thin periphragm and a thicker endophragm”. Cribroperidinium hadrum was described by Sarjeant (1966a, p. 119-121) from the late Barremian of the West Heslerton No. 1 borehole, where it was “quite frequent”. It was common to very common here, with a very restricted stratigraphic range (palynofloral Subzone LKP25.1) in Heslerton No. 2 (17.75 m and 17.00 m samples) and an isolated occurrence at the same level (11,143.00 ft) in well 22/26a-2.
Cribroperidinium hadrum (Sarjeant, 1966b, p.119–121, pl.14, fig.1; text-fig.28) Duxbury, 2019, p.185. Emendation: Duxbury (2019, p.184), as Cribroperidinium. Holotype: Sarjeant, 1966b, pl.14, fig.1. Originally Gonyaulacysta, subsequently Millioudodinium, thirdly Rhynchodiniopsis, fourthly Leptodinium?, fifthly (and now) Cribroperidinium. Age: late Barremian.
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Original diagnosis: Sarjeant, 1966, p. 119: Gonyaulacysta hadra
A Gonyaulacysta with thick-walled, spherical to spheroidal shell and long, tapering apical horn. Tabulation 4', ?oa, 6'', 6c, 6''', 1p, 1p.v., 1''''; poorly marked by crests in form of very low ridges bearing well spaced, extremely abbreviate spinelets. Cingulum weakly spiral: sulcus short, confined to ventral region. Surface generally densely granular.
Dimensions: holotype: overall length 151 µm, breadth 117 µm. Shell length 117 µm; length of horn 34 µm; breadth of cingulum c.7 µm. Paratype: overall length 145 µm, breadth c.112 µm; shell length 105 µm; length of horn 40 µm; breadth of cingulum c.5 µm. Range: overall length c.140-155 µm.
Original description: Sarjeant, 1966, p. 120-121: Gonyaulacysta hadra
This is an unusually large and very characteristic species, quite frequent at this horizon, some 20 specimens having been studied. The dense granulation and relatively inconspicuous character of the crests render the tabulation difficult to determine: Text-fig. 28 was prepared from study of several specimens and is unlikely to be accurate in detail. On most specimens, including the holotype, granules are absent from various small patches of the surface: this appears to result from damage. Granulation is consistently faint or lacking on the sulcus, which is somewhat sunken.
The test is spherical to spheroidal and composed of two distinct layers; a fairly thin periphragm and a thicker endophragm. The endophragm bulges only into the base of the apical horn, so that the horn contains a cavity between the wall layers. Four apical plates are present, jointly forming the apical horn. Plate 1' is long and broad, occupying the anterior prolongation of the sulcus. An anterior inter-
calary plate could not be determined. Six precingular plates are present, plates 1'' and 6'' being reduced. There are also six postcingular plates, with plate 1''' reduced to accommodate the large posterior intercalary plate. A narrow posterior ventral plate separates the polygonal antapical plate from the sulcus.
The cingulum forms a feebly laevorotatory spiral, its two ends scarcely differing in antero-posterior position. The sulcus is short, extending only over the middle third of the ventral surface: it is widest at mid-point and tapers to anterior and posterior.
A precingular archaeopyle, formed by loss of plate 3'', is present in all specimens seen.
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Emended diagnosis Duxbury, 2019
Emended Diagnosis: A very large, ovoidal, proximate cyst with a prominent, tapering, blunt-ended apical horn approximately one quarter of the cyst length. Autophragm very thick and fibro-perforate, without surface ornament and forming a broad, rounded apical protuberance. A very thin outer membrane covers the cyst and bears low surface ridges outlining a tabulation typical for the genus. Some separation of wall layers can be particularly prominent around the cingulum and at the antapex; the longer, distal part of the apical horn appears to be constructed of this outer layer. Archeopyle large, single-plate precingular (3''), operculum free.
Remarks: The questionable transfer of this species to Leptodinium Klement 1960 by Helenes (1984, p. 131) is rejected here. His comment that “Sarjeant’s (in Davey et al. 1966) text-figure 28 suggests the presence of quadrate X and Z paraplates” is negated by Sarjeant’s comment (1966a, p. 120) that, “Text-figure 28 was prepared from study of several specimens and is unlikely to be accurate in detail”. In the present study, despite the common occurrence of this species, distortion of the low sutural ridges has also precluded detailed analysis of the tabulation. However, the general form and (where discernible) tabulation of this species allows its positive assignment to Cribroperidinium.
Cribroperidinium hadrum is characterised by its very large size, thick autophragm and lack of prominent surface ornament. The surface of other large species, including Cribroperidinium edwardsii (Cookson and Eisenack 1958) Davey 1969 tends to be covered with verrucae, short spines or tubercles which are often aligned. Fourteen specimens were measured here, with the following dimensions – length 162(138)104 μm x breadth 129(113)89 μm, very similar to those quoted by Sarjeant (1966a, p. 120).
This species is also characterised by what appears to be a thin, “loose-fitting”, finely-wrinkled outer membrane over which run very low ridges marking the tabulation. This membrane might generally be termed an ectophragm, as described by Evitt (1985, p. 65) although it is typically separate from the autophragm around the cingulum (suturocavation beneath each cingular ridge) and at the antapex. Also, the long apical horn appears to be mainly formed by this outer layer (Plate 8, Figures 1, 3, 5).
Divergence of wall layers in Cribroperidinium has been discussed above for C. cornutum, a species which also shows cingular and antapical wall separation; this feature is much more extreme in C. cornutum than in C. hadrum. Helenes’s (1984, p. 112) description of the wall structure of Cribroperidinium as autophragm which may be differentiated into a homogeneous and structureless inner part and a vesicular to “spongy looking” outer part, without separation of layers does not accurately describe C. hadrum or C. cornutum. It is the opposite particularly of what is seen in C. hadrum, which has a thick “spongy-looking” inner and a very thin outer layer as noted by Sarjeant (1966a, p. 120), who described “two distinct layers; a fairly thin periphragm and a thicker endophragm”. Cribroperidinium hadrum was described by Sarjeant (1966a, p. 119-121) from the late Barremian of the West Heslerton No. 1 borehole, where it was “quite frequent”. It was common to very common here, with a very restricted stratigraphic range (palynofloral Subzone LKP25.1) in Heslerton No. 2 (17.75 m and 17.00 m samples) and an isolated occurrence at the same level (11,143.00 ft) in well 22/26a-2.