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Wrevittia cassidata
Wrevittia cassidata (Eisenack and Cookson, 1960, p.3, pl.1, figs.5-6) Helenes and Lucas-Clark, 1997, p.188; Emendations: Sarjeant, 1966b, p.125, as Gonyaulacysta cassidata; Helenes and Lucas-Clark, 1997, p.190, as Wrevittia cassidata.
Originally Gonyaulax helicoidea subsp. cassidata, subsequently Gonyaulax cassidata, thirdly Gonyaulacysta cassidata, fourthly (and now) Wrevittia cassidata.
Holotype: Eisenack and Cookson, 1960, pl.1, fig.5; Jan du Chêne et al., 1986a, pl.40, figs.6-7.
Age: Aptian-Cenomanian.
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G.L. Williams short notes on species, Mesozoic-Cenozoic dinocyst course, Urbino, Italy, May 17-22, 1999 -
Wrevittia cassidata (Eisenack and Cookson, 1960) Helenes and Lucas-Clark, 1997, emend. Sarjeant, 1966b, emend. Helenes and Lucas-Clark, 1997. Emended diagnosis from Helenes and Lucas-Clark (1997, p.190), proximate cysts with elongate ovoidal to subhexagonal body and an apical horn. Precingular archeopyle type P4. Peri- and endophragm appressed except under the apical region and beneath parasutural ridges. Apical region usually prominently cavate, characterized by the presence of two infundibula located in the position of paraplates B and C. Parasutural ridges low to high, smooth, serrate or spiny, varying even within one specimen and commonly between specimens. Paratabulation pattern conforming to that described for Wrevittia. Intratabular features range from smooth wall to small granules sometimes elevated almost to spines, to numerous thick granules. Equatorial diameter about 35 µm, body length about 50 µm, height of apical horn about 15 µm. Size: length 71-95 µm, width 47-57 µm.
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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.
Originally Gonyaulax helicoidea subsp. cassidata, subsequently Gonyaulax cassidata, thirdly Gonyaulacysta cassidata, fourthly (and now) Wrevittia cassidata.
Holotype: Eisenack and Cookson, 1960, pl.1, fig.5; Jan du Chêne et al., 1986a, pl.40, figs.6-7.
Age: Aptian-Cenomanian.
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G.L. Williams short notes on species, Mesozoic-Cenozoic dinocyst course, Urbino, Italy, May 17-22, 1999 -
Wrevittia cassidata (Eisenack and Cookson, 1960) Helenes and Lucas-Clark, 1997, emend. Sarjeant, 1966b, emend. Helenes and Lucas-Clark, 1997. Emended diagnosis from Helenes and Lucas-Clark (1997, p.190), proximate cysts with elongate ovoidal to subhexagonal body and an apical horn. Precingular archeopyle type P4. Peri- and endophragm appressed except under the apical region and beneath parasutural ridges. Apical region usually prominently cavate, characterized by the presence of two infundibula located in the position of paraplates B and C. Parasutural ridges low to high, smooth, serrate or spiny, varying even within one specimen and commonly between specimens. Paratabulation pattern conforming to that described for Wrevittia. Intratabular features range from smooth wall to small granules sometimes elevated almost to spines, to numerous thick granules. Equatorial diameter about 35 µm, body length about 50 µm, height of apical horn about 15 µm. Size: length 71-95 µm, width 47-57 µm.
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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.