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Gonyaulacysta cassidata
Gonyaulacysta "cassidata" (Eisenack and Cookson, 1960, p.3, pl.1, figs.5-6) Sarjeant, 1966b, p.125-126. Emendations: Sarjeant, 1966b, p.125, as Gonyaulacysta cassidata; Helenes and Lucas-Clark, 1997, p.190, as Wrevittia cassidata.
Holotype: Eisenack and Cookson, 1960, pl.1, fig.5; Jan du Chêne et al., 1986a, pl.40, figs.6-7. NOW Wrevittia cassidata. Originally Gonyaulax helicoidea subsp. cassidata, subsequently Gonyaulax cassidata, thirdly Gonyaulacysta cassidata, fourthly (and now) Wrevittia cassidata.
Stratum typicum: Aptian-Cenomanian
Translation Vozzhennikova, 1967: Lees, 1971
Original description: Eisenack and Cookson, 1960, p. 3: Gonyaulax helicoidea subsp. cassidata
Diagnosis: Apex more prominent than in G. helicoidea s.s., dome-shaped, narrowing abruptly to a bluntly pointed horn; antapical region with a projection formed by the ledges and supported by thin spines deriving from the corners of the antapical plate 1"""".
Dimensions: Type- 83 µm long, 52 µm broad. Range 71-95 µm long, 47- 57 µm broad.
Emended description: Sarjeant, 1966, p. 126-127
Diagnosis: A Gonyaulacysta with thin-walled, broadly ovoidal theca, surmounted by apical pericoel terminating in short horn. Tabulation 4", 1a, 6"", 6c, 6""", 1p, I""""; plate boundaries demarcated by high, delicate crests with smooth or denticulate edges. Cingulum strongly spiral, of moderate breadth: sulcus broadening posteriorly, weakly sigmoidal. (A median dorso-ventral plane would barely intersect the two ends of the cingulum.) Surface of shell smooth or only minutely granular: irregular scatter of tubercles present in some specimens.
Dimensions: Holotype: overall length 83 µm, breadth 52 µm. Range of Australian
specimens: overall lengths 71 to 95 µm, breadths 47 to 57 µm. Figured specimen:
overall length 78 µm, breadth 53 µm, shell length 42 µm, breadth 45 µm. Range of English specimens: overall lengths 60 to 78 µm, breadths 46 to 53 µm.
Description: Shell broadly ovoidal, the apical pericoel and high antapical crests imparting a polygonal appearance. The crests separating the four apical plates converge at the top of the apical horn, which has a bifid appearance. Plate 1" is elongate but relatively short, occupying the anterior prolongation of the sulcus.
The apical pericoel comprises the apical plates, the anterior intercalary plate and the anterior portions of the six precingular plates: its volume is between one-third and two-thirds that of the shell proper. The anterior plate is somewhat elongate:
plate 6"" is reduced and almost triangular. Six postcingular plates are present.
Plate 1""" is reduced and linear, diffficult to see in many specimens: it is displaced by the posterior broadening of the sulcus. A small, quadrate posterior intercalary plate separates plates 1""" and 2""" from the single, polygonal antapical plate.
The cingulum forms a laevorotatory spiral such that its two ends differ in antero posterior position by over twice its width. It is composed of six plates. The sulcus is of moderate breadth on the epitract but broadens considerably as it approaches the antapex.
The shell wall and the crests are both delicate. The crests are high, typically but not consistently denticulate, sometimes minutely and irregularly perforate: the very high crests surrounding the antapex appear to be sustained by delicate spines at the angles. Tubercles may be present; their number and distribution varies considerably between individuals.
A precingular archaeopyle is formed by loss of plate 3"": in some specimens, including the figured specimen, the cingulum is slightly torn also.
Supplemental description: Vozzhennikova, 1967
Theca ovoid with a cupola-like apex and a truncated antapex. The cupola-like part of the armour tapers to give a small bluntly ended horn. The structure appears to be formed from the apical and anterior equatorial plates which are bent round at their ends. The transverse furrow spirals to the left, the two ends of the furrow being seperated by a distance equal to half the width of the furrow itself. The longitudinal furrow lies oblique to the longitudinal axis of the cell. Plate formula on the epitheca 4a+6np, on the hypotheca 6zd+1cp"+1a"+?hnb. The anterior equatorial plates are trapeziform and relatively large except for 6np which is smaller than the others; a pylome accurs in place of 3np. The plates of the hypotheca differ in size and shape. Plate 1zd is long and narrow and adjoins the small plate 2zd. Plates 3zd, 4zd and 5zd are large, 6zd is somewhat smaller. Between the antapical plates and plates 1zd and 2zd there is a small accessory plate. In addition there may well be a further plate (hnb?) between the antapical plate and the longitudinal furrow, this plate is difficult to discern because of the toothd processes of the surrounding plates. Similar processes occur on the margin of the transverse furrow. The shape of the antapical plates is indistinct; they are however provided with a toothed marginal flange.
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Gonyaulacysta aff. G. cassidata of Nohr-Hansen 1993
Comments: Nohr-Hansen 1993:
The few specimens hereby assigned to G. aff. G. cassidata have less pronounced tubercles and are slightly shorter than the type material.
Occurence in east Greenland. The species has only been recorded from the upper Barremian section 1, and the Aptian section 13.
Previous occurrences: Gonyaulacysta cassidata was previously recorded from the Cenomanina, England (Sarjeant 1966a), the lower Aptian to upper Cenomanina, England and the North Sea (Costa and Davey 1992), the lower Barremian to upper Cenomanian, north-west Germany (Prössl 1990) and world-wide from the upper Hauterivian to lower Turonian (Williams and Bujak 1985). The type material was described from the Aptian to Cenomanian in Australia by Eisenack and Cookson (1960).
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Holotype: Eisenack and Cookson, 1960, pl.1, fig.5; Jan du Chêne et al., 1986a, pl.40, figs.6-7. NOW Wrevittia cassidata. Originally Gonyaulax helicoidea subsp. cassidata, subsequently Gonyaulax cassidata, thirdly Gonyaulacysta cassidata, fourthly (and now) Wrevittia cassidata.
Stratum typicum: Aptian-Cenomanian
Translation Vozzhennikova, 1967: Lees, 1971
Original description: Eisenack and Cookson, 1960, p. 3: Gonyaulax helicoidea subsp. cassidata
Diagnosis: Apex more prominent than in G. helicoidea s.s., dome-shaped, narrowing abruptly to a bluntly pointed horn; antapical region with a projection formed by the ledges and supported by thin spines deriving from the corners of the antapical plate 1"""".
Dimensions: Type- 83 µm long, 52 µm broad. Range 71-95 µm long, 47- 57 µm broad.
Emended description: Sarjeant, 1966, p. 126-127
Diagnosis: A Gonyaulacysta with thin-walled, broadly ovoidal theca, surmounted by apical pericoel terminating in short horn. Tabulation 4", 1a, 6"", 6c, 6""", 1p, I""""; plate boundaries demarcated by high, delicate crests with smooth or denticulate edges. Cingulum strongly spiral, of moderate breadth: sulcus broadening posteriorly, weakly sigmoidal. (A median dorso-ventral plane would barely intersect the two ends of the cingulum.) Surface of shell smooth or only minutely granular: irregular scatter of tubercles present in some specimens.
Dimensions: Holotype: overall length 83 µm, breadth 52 µm. Range of Australian
specimens: overall lengths 71 to 95 µm, breadths 47 to 57 µm. Figured specimen:
overall length 78 µm, breadth 53 µm, shell length 42 µm, breadth 45 µm. Range of English specimens: overall lengths 60 to 78 µm, breadths 46 to 53 µm.
Description: Shell broadly ovoidal, the apical pericoel and high antapical crests imparting a polygonal appearance. The crests separating the four apical plates converge at the top of the apical horn, which has a bifid appearance. Plate 1" is elongate but relatively short, occupying the anterior prolongation of the sulcus.
The apical pericoel comprises the apical plates, the anterior intercalary plate and the anterior portions of the six precingular plates: its volume is between one-third and two-thirds that of the shell proper. The anterior plate is somewhat elongate:
plate 6"" is reduced and almost triangular. Six postcingular plates are present.
Plate 1""" is reduced and linear, diffficult to see in many specimens: it is displaced by the posterior broadening of the sulcus. A small, quadrate posterior intercalary plate separates plates 1""" and 2""" from the single, polygonal antapical plate.
The cingulum forms a laevorotatory spiral such that its two ends differ in antero posterior position by over twice its width. It is composed of six plates. The sulcus is of moderate breadth on the epitract but broadens considerably as it approaches the antapex.
The shell wall and the crests are both delicate. The crests are high, typically but not consistently denticulate, sometimes minutely and irregularly perforate: the very high crests surrounding the antapex appear to be sustained by delicate spines at the angles. Tubercles may be present; their number and distribution varies considerably between individuals.
A precingular archaeopyle is formed by loss of plate 3"": in some specimens, including the figured specimen, the cingulum is slightly torn also.
Supplemental description: Vozzhennikova, 1967
Theca ovoid with a cupola-like apex and a truncated antapex. The cupola-like part of the armour tapers to give a small bluntly ended horn. The structure appears to be formed from the apical and anterior equatorial plates which are bent round at their ends. The transverse furrow spirals to the left, the two ends of the furrow being seperated by a distance equal to half the width of the furrow itself. The longitudinal furrow lies oblique to the longitudinal axis of the cell. Plate formula on the epitheca 4a+6np, on the hypotheca 6zd+1cp"+1a"+?hnb. The anterior equatorial plates are trapeziform and relatively large except for 6np which is smaller than the others; a pylome accurs in place of 3np. The plates of the hypotheca differ in size and shape. Plate 1zd is long and narrow and adjoins the small plate 2zd. Plates 3zd, 4zd and 5zd are large, 6zd is somewhat smaller. Between the antapical plates and plates 1zd and 2zd there is a small accessory plate. In addition there may well be a further plate (hnb?) between the antapical plate and the longitudinal furrow, this plate is difficult to discern because of the toothd processes of the surrounding plates. Similar processes occur on the margin of the transverse furrow. The shape of the antapical plates is indistinct; they are however provided with a toothed marginal flange.
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Gonyaulacysta aff. G. cassidata of Nohr-Hansen 1993
Comments: Nohr-Hansen 1993:
The few specimens hereby assigned to G. aff. G. cassidata have less pronounced tubercles and are slightly shorter than the type material.
Occurence in east Greenland. The species has only been recorded from the upper Barremian section 1, and the Aptian section 13.
Previous occurrences: Gonyaulacysta cassidata was previously recorded from the Cenomanina, England (Sarjeant 1966a), the lower Aptian to upper Cenomanina, England and the North Sea (Costa and Davey 1992), the lower Barremian to upper Cenomanian, north-west Germany (Prössl 1990) and world-wide from the upper Hauterivian to lower Turonian (Williams and Bujak 1985). The type material was described from the Aptian to Cenomanian in Australia by Eisenack and Cookson (1960).
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