Back
Cribroperidinium ornatum
From Fensome et al., 2019:
Cribroperidinium ornatum Duxbury, 2019, p.185–186, pl.10, figs.1–3,6,9. Holotype: Duxbury, 2019, pl.10, figs.1–3. Age: late Barremian.
---------------------------------------------------------------------------------------------------
Original description Duxbury, 2019
Holotype: Plate 10, Figures 1–3.
Type Locality: Well 22/26a-2 at 11,181.33 ft (core chip), late Barremian age. Holotype: E.F. K48.0.
Derivation of Name: From the Latin orno, ornatus, decorate, furnish - in reference to the surface complexity of this species.
Diagnosis: A moderately thick-walled, spheroidal proximate cyst, autophragm only, the epicyst slightly shorter than the hypocyst. A fairly coarse, spiny reticulum covers the surface and a tabulation apparently typical of the genus is outlined by relatively high, distally-entire, fenestrate sutural crests. Reticular spine height equals that of the sutural crests. A prominent, spiny apical horn is invariably present . The archeopyle is formed by loss of a single precingular plate (3''), operculum free.
Dimensions: Holotype: 73 × 78 μm.
Overall: 81 (73) 68 μm × 78 (68) 63 μm.
Specimens Measured: 7.
Remarks: This very distinctive species of Cribroperidinium is characterised mainly by its fairly coarse, spiny surface reticulum and the distally entire, fenestrate sutural crests. The overall shape of this species and its distinctive sutural crests are reminiscent of Cribroperidinium episomum. In addition, C. episomum can bear a few intratabular, lightly striate spines very similar to, but much rarer than, those of C. ornatum. In its reticulate surface ornament and spines, C. ornatum resembles Cribroperidinium spinoreticulatum (McIntyre and Brideaux 1980) Århus 1992 and Cribroperidinium comptum (Duxbury 1980) Lentin and Williams 1981, although the more rounded shape, coarser surface reticulum, longer spines and distally-entire, fenestrate sutural crests set C. ornatum apart from the last two species. Cribroperidinium ornatum was recorded from only one sample, at 11,181.33 ft (late Barremian) in well 22/26a-2. Genus Cyclonephelium Deflandre and Cookson 1955 Type: Deflandre and Cookson, 1955, Plate 2, Figure 12, as Cyclonephelium compactum
Remarks: Like Harding (1990, p. 19), the present author recognises the wide range of cyst morphologies encompassed within this genus and the difficulty in differentiating effectively be tween taxa. Harding (op. cit.) recognised three species of Cyclonephelium, C. distinctum Deflandre and Cookson 1955 and the informal taxa, Cyclonephelium sp. I and Cyclonephelium sp. II.
One reason for Harding’s informal treatment appears to be Evitt’s (1985, p. 214) comment that variability is likely to reflect palaeoenvironmental conditions. However, the effects of changing palaeoenvironmental conditions on dinocyst assemblages would presumably extend beyond a particular genus, affecting many taxa, with adaptation to these changes reflected in various intra-specific trends. An example of this concerns Muderongia Cookson and Eisenack 1958 and similar genera, including Vesperopsis Bint 1986 and Nyktericysta Bint 1986, where differences in the number of wall layers, degree of wall layer separation, surface ornament and style of excystment (adnate or free operculum) are considered particularly important. Which, if any, dinocyst characteristics are particularly palaeoenvironmentally sensitive is difficult to assess at present (see remarks under Muderongia patula Duxbury n. sp., below). In the present study, one of Harding’s informal taxa, Cyclonephelium sp. II appears to be a particularly valuable marker, having a very restricted age range within the late Barremian, and this species is formalised below, as Cyclonephelium crebrum Duxbury n. sp.
Cribroperidinium ornatum Duxbury, 2019, p.185–186, pl.10, figs.1–3,6,9. Holotype: Duxbury, 2019, pl.10, figs.1–3. Age: late Barremian.
---------------------------------------------------------------------------------------------------
Original description Duxbury, 2019
Holotype: Plate 10, Figures 1–3.
Type Locality: Well 22/26a-2 at 11,181.33 ft (core chip), late Barremian age. Holotype: E.F. K48.0.
Derivation of Name: From the Latin orno, ornatus, decorate, furnish - in reference to the surface complexity of this species.
Diagnosis: A moderately thick-walled, spheroidal proximate cyst, autophragm only, the epicyst slightly shorter than the hypocyst. A fairly coarse, spiny reticulum covers the surface and a tabulation apparently typical of the genus is outlined by relatively high, distally-entire, fenestrate sutural crests. Reticular spine height equals that of the sutural crests. A prominent, spiny apical horn is invariably present . The archeopyle is formed by loss of a single precingular plate (3''), operculum free.
Dimensions: Holotype: 73 × 78 μm.
Overall: 81 (73) 68 μm × 78 (68) 63 μm.
Specimens Measured: 7.
Remarks: This very distinctive species of Cribroperidinium is characterised mainly by its fairly coarse, spiny surface reticulum and the distally entire, fenestrate sutural crests. The overall shape of this species and its distinctive sutural crests are reminiscent of Cribroperidinium episomum. In addition, C. episomum can bear a few intratabular, lightly striate spines very similar to, but much rarer than, those of C. ornatum. In its reticulate surface ornament and spines, C. ornatum resembles Cribroperidinium spinoreticulatum (McIntyre and Brideaux 1980) Århus 1992 and Cribroperidinium comptum (Duxbury 1980) Lentin and Williams 1981, although the more rounded shape, coarser surface reticulum, longer spines and distally-entire, fenestrate sutural crests set C. ornatum apart from the last two species. Cribroperidinium ornatum was recorded from only one sample, at 11,181.33 ft (late Barremian) in well 22/26a-2. Genus Cyclonephelium Deflandre and Cookson 1955 Type: Deflandre and Cookson, 1955, Plate 2, Figure 12, as Cyclonephelium compactum
Remarks: Like Harding (1990, p. 19), the present author recognises the wide range of cyst morphologies encompassed within this genus and the difficulty in differentiating effectively be tween taxa. Harding (op. cit.) recognised three species of Cyclonephelium, C. distinctum Deflandre and Cookson 1955 and the informal taxa, Cyclonephelium sp. I and Cyclonephelium sp. II.
One reason for Harding’s informal treatment appears to be Evitt’s (1985, p. 214) comment that variability is likely to reflect palaeoenvironmental conditions. However, the effects of changing palaeoenvironmental conditions on dinocyst assemblages would presumably extend beyond a particular genus, affecting many taxa, with adaptation to these changes reflected in various intra-specific trends. An example of this concerns Muderongia Cookson and Eisenack 1958 and similar genera, including Vesperopsis Bint 1986 and Nyktericysta Bint 1986, where differences in the number of wall layers, degree of wall layer separation, surface ornament and style of excystment (adnate or free operculum) are considered particularly important. Which, if any, dinocyst characteristics are particularly palaeoenvironmentally sensitive is difficult to assess at present (see remarks under Muderongia patula Duxbury n. sp., below). In the present study, one of Harding’s informal taxa, Cyclonephelium sp. II appears to be a particularly valuable marker, having a very restricted age range within the late Barremian, and this species is formalised below, as Cyclonephelium crebrum Duxbury n. sp.