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Occisucysta cornuta
Occisucysta cornuta (Davey, 1974) Below, 1981
Now Cribroperidinium?. Originally Cribroperidinium, subsequently Occisucysta, thirdly (and now) Cribroperidinium?.
Lentin and Williams, 1981, retained the species in Cribroperidinium Neale and Sarjeant, 1962.
Holotype: Davey, 1974, pl.2, figs.2-3; Jan du Chêne et al., 1986, pl.21, figs.8-9
Paratype: Davey, 1974
Locus typicus: Speeton, England
Stratum typicum: Middle-Late Barremian
Original diagnosis: Davey, 1974, p.48
A species of Cribroperidinium possessing a thick walled, spherical to subspherical central body and a thin, smooth to lightly pitted outer wall. Crests well defined and partly membranous. The apical horn, formed only from the outer wall, is very strongly developed; it is broad-based and tapers distally. In the cingular region the outer wall is raised laterally to form a distinctive encircling flange. This wall is similarly raised in the antapical region to form a subangular extension. Extensive apical, cingular and antaplcal pericoels (cavities) are present. The precingular operculum (3") is large and often remains in position; it bears a rounded Y-shaped crest.
DimensionsHolotypeParatypeRange
Overall length 123 µm138 µm117(124)138 µm
Overall width 88 µm 94 µm 79 (83) 94 µm
Apical horn 37 µm 38 µm 30 (36) 42 µm
Cingular extension 12 µm12 µm 8 (10) 12 µm
Antapica extension 13 µm 15 µm 8 (11) 15 µm
Original description: Davey, 1974, p.48
The inner wall is thick varying from 2 µm to up to 5 µm in the thickened apical and antapical regions. The outer wall is generally thin (under 1 µm) and is raised up to form crests--here this wall may be thicker. The crests are typical of this genus (see Davey, 1969) and define basically a Gonyaulax-type tabulation with additional intra-tabular crests. The crests sometimes develop fine membIanes which may be entire distally or quite often form short, blunt spines. Surface tubercles are absent. The cingular extension of the outer wall is often distorted but is always clearly visible at the lateral margins of the cyst. The cingulum is relatively narrow (approximately 5 µm in width) and appears not to bear plates. The sulcus only just extends onto the epitract, it widens abruptly at the cingulum and is not tabulate.
Affinities:
Davey, 1974, p.48: The combination of large size, Cribroperidium-type tabulation, strong apical horn and lateral and antapical extensions of the outer wall, with attendent pericoel, make C. cornutum a distinctive species. The development of pericoels in this species is an unusual feature which may be compared with their development in the Gonyaulacysta cassidata (Eisenack and Cookson) Psaligonyaulax deflandrei Sarjeant lineage.
The most similar species to C. cornutum are Gonyaulacysta scotti (Cookson and Eisenack) and G. perforans (Cookson and Eisenack) from the Upper Jurassic of Australia and Papua respectively. In some specimens of these species the antapical and lateral outer wall extensions are comparable to C. cornutum; however, the similarity is superficial since both forms have a normal Gonyaulax-type tabulation without additional crests, and the apical horns are relatively poorly developed. The specimens described as Gonyaulax perforans by Alberti (1961) are identical with C. cornutum and, as in the present study, are found in the Upper Barremian.
Now Cribroperidinium?. Originally Cribroperidinium, subsequently Occisucysta, thirdly (and now) Cribroperidinium?.
Lentin and Williams, 1981, retained the species in Cribroperidinium Neale and Sarjeant, 1962.
Holotype: Davey, 1974, pl.2, figs.2-3; Jan du Chêne et al., 1986, pl.21, figs.8-9
Paratype: Davey, 1974
Locus typicus: Speeton, England
Stratum typicum: Middle-Late Barremian
Original diagnosis: Davey, 1974, p.48
A species of Cribroperidinium possessing a thick walled, spherical to subspherical central body and a thin, smooth to lightly pitted outer wall. Crests well defined and partly membranous. The apical horn, formed only from the outer wall, is very strongly developed; it is broad-based and tapers distally. In the cingular region the outer wall is raised laterally to form a distinctive encircling flange. This wall is similarly raised in the antapical region to form a subangular extension. Extensive apical, cingular and antaplcal pericoels (cavities) are present. The precingular operculum (3") is large and often remains in position; it bears a rounded Y-shaped crest.
DimensionsHolotypeParatypeRange
Overall length 123 µm138 µm117(124)138 µm
Overall width 88 µm 94 µm 79 (83) 94 µm
Apical horn 37 µm 38 µm 30 (36) 42 µm
Cingular extension 12 µm12 µm 8 (10) 12 µm
Antapica extension 13 µm 15 µm 8 (11) 15 µm
Original description: Davey, 1974, p.48
The inner wall is thick varying from 2 µm to up to 5 µm in the thickened apical and antapical regions. The outer wall is generally thin (under 1 µm) and is raised up to form crests--here this wall may be thicker. The crests are typical of this genus (see Davey, 1969) and define basically a Gonyaulax-type tabulation with additional intra-tabular crests. The crests sometimes develop fine membIanes which may be entire distally or quite often form short, blunt spines. Surface tubercles are absent. The cingular extension of the outer wall is often distorted but is always clearly visible at the lateral margins of the cyst. The cingulum is relatively narrow (approximately 5 µm in width) and appears not to bear plates. The sulcus only just extends onto the epitract, it widens abruptly at the cingulum and is not tabulate.
Affinities:
Davey, 1974, p.48: The combination of large size, Cribroperidium-type tabulation, strong apical horn and lateral and antapical extensions of the outer wall, with attendent pericoel, make C. cornutum a distinctive species. The development of pericoels in this species is an unusual feature which may be compared with their development in the Gonyaulacysta cassidata (Eisenack and Cookson) Psaligonyaulax deflandrei Sarjeant lineage.
The most similar species to C. cornutum are Gonyaulacysta scotti (Cookson and Eisenack) and G. perforans (Cookson and Eisenack) from the Upper Jurassic of Australia and Papua respectively. In some specimens of these species the antapical and lateral outer wall extensions are comparable to C. cornutum; however, the similarity is superficial since both forms have a normal Gonyaulax-type tabulation without additional crests, and the apical horns are relatively poorly developed. The specimens described as Gonyaulax perforans by Alberti (1961) are identical with C. cornutum and, as in the present study, are found in the Upper Barremian.