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Cribroperidinium episomum
From Fensome et al., 2019:
Cribroperidinium episomum (Sarjeant, 1966b, p.118–119, pl.13, figs.9–10; text-fig.27) Duxbury, 2019, p.184. Emendation: Duxbury (2019, p.184), as Cribroperidinium. Holotype: Sarjeant, 1966b, pl.13, figs.9–10; text-fig.27; Jan du Chêne et al., 1986a, pl.67, figs.15–16. Originally Gonyaulacysta, subsequently Millioudodinium, thirdly Rhynchodiniopsis, fourthly Leptodinium, fifthly (and now) Cribroperidinium. Taxonomic junior synonym: Cribroperidinium boreas, according to Duxbury (2019, p.184). Age: late Barremian.
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Original description: [Sarjeant, 1966b]:
Gonyaulacysta episoma sp. nov.
Pl. 13, figs. 9, 10; Text-fig. 27
DERIVATION OF NAME. Greek, episomos, bulky, fat—referring to the rotund shell shape.
DIAGNOSIS. A Gonyaulacysta with spherical to broadly ovoid shell with strong apical horn of moderate length. Tabulation 4’, 1a, 6”, ?5c, 6’'’, 1p, 1 p.v., 1"".
Crests consisting of rows of thin spinelets connected distally by trabeculum ; an extremely delicate membrane stretching between spinelets and trabecula. Cingulum strongly spiral ; sulcus broad and short, stretching from about mid-point on epitheca to about mid-point on hypotheca. Surface densely granular ; very few spines occasionally present. Horn with trifurcate appearance produced by high crest bounding plate 4’.
HOLOTYPE. B.M.(N.H.) slide V.51730(1). Speeton Clay, Shell West Heslerton Borehole No. 1, West Heslerton, Yorks., at 19-25 metres depth, Lower Cretaceous (Upper Barremian).
DIMENSIONS. Holotype: overall length 80μ, breadth 74μ ; shell length 70μ, breadth 68μ ; horn 10μ in length ; crests c.2μ in height ; cingulum c.3μ broad.
Range of dimensions : overall length 80-95μ, horn length 10-18μ, breadth 60-80μ.
DESCRIPTION. An abundant species at this horizon, some 30 specimens having been examined. All show some degree of distortion as a result of compression of the originally spherical, fairly thin-walled shell. The horn is short, strongly tapering and pointed ; it is tipped by plate 4’, the high crest bounding this plate producing a characteristic trifurcate appearance. There are four apical plates, plate 1’ occupying the anterior prolongation of the sulcus and being unusually broad. Six precingular plates are present, the sixth being reduced to accommodate the anterior intercalary plate. Six postcingular plates are present, plate 1’’’ being reduced to accommodate the posterior intercalary plate. A roughly quadrate posterior ventral plate separates the sulcus from the single large antapical plate. The cingulum is of moderate breadth and forms a strong laevorotatory spiral such that its two ends differ in antero-posterior position by three times its breadth. It comprises certainly five, possibly six cingular plates. The sulcus is short and broad. The surface is densely granular. In at least one specimen (figured), a very few short spines are present on the surface of the hypotract : spines are not present, however, on the holotype. The degree of granulation of the sulcus is markedly less than that of the rest of the surface.
A precingular archaeopyle, formed by loss of plate 3”, is present in all specimens seen.
REMARKS. Gonyaulacysta episoma sp. nov. is characterized by its combination of shape, tabulation and crest character. Gonyaulacysta nuciformis (Deflandre 1938), from the Upper Jurassic, has a somewhat similar overall shape and degree of granulation, but the shell wall is thicker, the tabulation is less clear and the form of the crests is quite different. Gonyaulacysta scotti (Cookson & Eisenack 1958) an inadequately described species from the Upper Jurassic of Western Australia, has rather similar crests, but has a more markedly ovoidal shape and an apical horn of dissimilar type. Gonyaulacysta tenuiceras (Eisenack 1958) from the Aptian of Germany, has a horn and crests of somewhat similar character, but the crests are much higher and the tabulation is markedly different. A specimen figured as G. tenuiceras by Alberti (1961, pl. 11, fig. 7), from the Upper Barremian of Germany, may well be in fact G. episoma.
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Emended description: [Duxbury 2019]:
Emended Diagnosis: A spheroidal to ovoidal dinocyst with a broad apical horn. The cyst wall is of moderate thickness and fibroperforate, free of ornament or bearing intratabular, lightly-striate spines or tubercles. Sutural crests are relatively high, narrow and markedly fenestrate; individual fenestrations can be large, are generally oval and can extend from the cyst wall to the crestal margin, which is smooth. The cingulum divides the cyst into approximately equal halves; the displacement of the cingulum along the sulcus approximates the cingulum width. The reflected tabulation is 4', 6'', ?c, 6''', 1p, 1p.v., 1''''. A precingular archeopyle is formed by the detachment of plate 3''.
Remarks: Very similar descriptions of this species were offered by Sarjeant (1966a, p. 118, 119 - as Gonyaulacysta episoma) and Davey (1974, p. 52, 53 - as Gonyaulacysta boreas), with both authors emphasising the importance of the distinctive overall shape, tabulation and type of sutural crests. Remarkably, both authors also cited the similar crests of Cribroperidinium? scottii (Cookson and Eisenack 1958) Stover and Evitt 1978 and further similarities exhibited by Tehamadinium tenuiceras (Eisenack 1958) Jan du Chêne et al. 1986b. However, Davey (op. cit.) did not discuss C. episomum per se. The sutural crests of this species are particularly characteristic and were well illustrated by Davey (1974, Plate 4, Figure 4). Davey (op. cit., p. 53) described crestal perforations as, “so large that often the crests appear to consist of small membranous processes which are linked distally by trabeculae”, and Sarjeant (1966a, p. 118) described, “Crests consisting of rows of thin spinelets connected distally by trabeculum”. The size ranges quoted for this species by Sarjeant (op. cit., p. 118) and Davey (op. cit., p. 52) are very similar. Towards the top of its range, this species can be larger and more ornate than older material, although still with characteristically entire distal margins to the crests.
Cribroperidinium episomum was described by Sarjeant (op. cit.) from the late Barremian of the West Heslerton No. 1 borehole, where it was abundant and Davey (op. cit.) described it, as Gonyaulacysta boreas, from the late Barremian of the Speeton Clay outcrop. It was restricted to the late Barremian to early Aptian interval in the present study, ranging as young as palynofloral Zone LKP25.
Cribroperidinium episomum (Sarjeant, 1966b, p.118–119, pl.13, figs.9–10; text-fig.27) Duxbury, 2019, p.184. Emendation: Duxbury (2019, p.184), as Cribroperidinium. Holotype: Sarjeant, 1966b, pl.13, figs.9–10; text-fig.27; Jan du Chêne et al., 1986a, pl.67, figs.15–16. Originally Gonyaulacysta, subsequently Millioudodinium, thirdly Rhynchodiniopsis, fourthly Leptodinium, fifthly (and now) Cribroperidinium. Taxonomic junior synonym: Cribroperidinium boreas, according to Duxbury (2019, p.184). Age: late Barremian.
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Original description: [Sarjeant, 1966b]:
Gonyaulacysta episoma sp. nov.
Pl. 13, figs. 9, 10; Text-fig. 27
DERIVATION OF NAME. Greek, episomos, bulky, fat—referring to the rotund shell shape.
DIAGNOSIS. A Gonyaulacysta with spherical to broadly ovoid shell with strong apical horn of moderate length. Tabulation 4’, 1a, 6”, ?5c, 6’'’, 1p, 1 p.v., 1"".
Crests consisting of rows of thin spinelets connected distally by trabeculum ; an extremely delicate membrane stretching between spinelets and trabecula. Cingulum strongly spiral ; sulcus broad and short, stretching from about mid-point on epitheca to about mid-point on hypotheca. Surface densely granular ; very few spines occasionally present. Horn with trifurcate appearance produced by high crest bounding plate 4’.
HOLOTYPE. B.M.(N.H.) slide V.51730(1). Speeton Clay, Shell West Heslerton Borehole No. 1, West Heslerton, Yorks., at 19-25 metres depth, Lower Cretaceous (Upper Barremian).
DIMENSIONS. Holotype: overall length 80μ, breadth 74μ ; shell length 70μ, breadth 68μ ; horn 10μ in length ; crests c.2μ in height ; cingulum c.3μ broad.
Range of dimensions : overall length 80-95μ, horn length 10-18μ, breadth 60-80μ.
DESCRIPTION. An abundant species at this horizon, some 30 specimens having been examined. All show some degree of distortion as a result of compression of the originally spherical, fairly thin-walled shell. The horn is short, strongly tapering and pointed ; it is tipped by plate 4’, the high crest bounding this plate producing a characteristic trifurcate appearance. There are four apical plates, plate 1’ occupying the anterior prolongation of the sulcus and being unusually broad. Six precingular plates are present, the sixth being reduced to accommodate the anterior intercalary plate. Six postcingular plates are present, plate 1’’’ being reduced to accommodate the posterior intercalary plate. A roughly quadrate posterior ventral plate separates the sulcus from the single large antapical plate. The cingulum is of moderate breadth and forms a strong laevorotatory spiral such that its two ends differ in antero-posterior position by three times its breadth. It comprises certainly five, possibly six cingular plates. The sulcus is short and broad. The surface is densely granular. In at least one specimen (figured), a very few short spines are present on the surface of the hypotract : spines are not present, however, on the holotype. The degree of granulation of the sulcus is markedly less than that of the rest of the surface.
A precingular archaeopyle, formed by loss of plate 3”, is present in all specimens seen.
REMARKS. Gonyaulacysta episoma sp. nov. is characterized by its combination of shape, tabulation and crest character. Gonyaulacysta nuciformis (Deflandre 1938), from the Upper Jurassic, has a somewhat similar overall shape and degree of granulation, but the shell wall is thicker, the tabulation is less clear and the form of the crests is quite different. Gonyaulacysta scotti (Cookson & Eisenack 1958) an inadequately described species from the Upper Jurassic of Western Australia, has rather similar crests, but has a more markedly ovoidal shape and an apical horn of dissimilar type. Gonyaulacysta tenuiceras (Eisenack 1958) from the Aptian of Germany, has a horn and crests of somewhat similar character, but the crests are much higher and the tabulation is markedly different. A specimen figured as G. tenuiceras by Alberti (1961, pl. 11, fig. 7), from the Upper Barremian of Germany, may well be in fact G. episoma.
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Emended description: [Duxbury 2019]:
Emended Diagnosis: A spheroidal to ovoidal dinocyst with a broad apical horn. The cyst wall is of moderate thickness and fibroperforate, free of ornament or bearing intratabular, lightly-striate spines or tubercles. Sutural crests are relatively high, narrow and markedly fenestrate; individual fenestrations can be large, are generally oval and can extend from the cyst wall to the crestal margin, which is smooth. The cingulum divides the cyst into approximately equal halves; the displacement of the cingulum along the sulcus approximates the cingulum width. The reflected tabulation is 4', 6'', ?c, 6''', 1p, 1p.v., 1''''. A precingular archeopyle is formed by the detachment of plate 3''.
Remarks: Very similar descriptions of this species were offered by Sarjeant (1966a, p. 118, 119 - as Gonyaulacysta episoma) and Davey (1974, p. 52, 53 - as Gonyaulacysta boreas), with both authors emphasising the importance of the distinctive overall shape, tabulation and type of sutural crests. Remarkably, both authors also cited the similar crests of Cribroperidinium? scottii (Cookson and Eisenack 1958) Stover and Evitt 1978 and further similarities exhibited by Tehamadinium tenuiceras (Eisenack 1958) Jan du Chêne et al. 1986b. However, Davey (op. cit.) did not discuss C. episomum per se. The sutural crests of this species are particularly characteristic and were well illustrated by Davey (1974, Plate 4, Figure 4). Davey (op. cit., p. 53) described crestal perforations as, “so large that often the crests appear to consist of small membranous processes which are linked distally by trabeculae”, and Sarjeant (1966a, p. 118) described, “Crests consisting of rows of thin spinelets connected distally by trabeculum”. The size ranges quoted for this species by Sarjeant (op. cit., p. 118) and Davey (op. cit., p. 52) are very similar. Towards the top of its range, this species can be larger and more ornate than older material, although still with characteristically entire distal margins to the crests.
Cribroperidinium episomum was described by Sarjeant (op. cit.) from the late Barremian of the West Heslerton No. 1 borehole, where it was abundant and Davey (op. cit.) described it, as Gonyaulacysta boreas, from the late Barremian of the Speeton Clay outcrop. It was restricted to the late Barremian to early Aptian interval in the present study, ranging as young as palynofloral Zone LKP25.