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Wrevittia helicoidea
From Fensome et al., 2019:
Wrevittia helicoidea (Eisenack and Cookson, 1960, p.2–3, pl.1, figs.4–6,9 [figs.5-6 are now Wrevittia cassidata]) Helenes and Lucas-Clark, 1997, p.187.
Emendations: Sarjeant, 1966b, p.116, as Gonyaulacysta helicoidea; Helenes and Lucas-Clark, 1997, p.187–188, as Wrevittia helicoidea.
Holotype: Eisenack and Cookson, 1960, pl.1, fig.4; Jan du Chêne et al., 1986a, pl.40, figs.4–5.
Originally Gonyaulax (Appendix B), subsequently Gonyaulacysta, thirdly (and now) Wrevittia.
Taxonomic junior synonym: Gonyaulacysta (now Wrevittia?) diutina, according to Stover and Helby (1987d, p.287) -however, Jan du Chêne et al. (1986a, p.130) and Lentin and Williams (1989, p.152) retained Gonyaulacysta (now Wrevittia?) diutina.
Age: Neocomian–Aptian.
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Original description: Eisenackand Cookson, 1960, p.2
Shell broadly oval, unequally divided by a strongly helicoid girdle; epitheca longer than hypotheca, surmounded by a hollow, thin-walled conical projection with a blunt apex; hypotheca broadly rounded. Both the girdle and plates are bordered by relatively high ledges with serrate edges. The surface of the plates is ornamented to varying degrees with small irregularly scattered tubercles. The longitudinal furrow lies +/- obliquely to the long axis. A pylome may be developed by the removal of plate 3"".
Dimensions: Range: 62-86 µm long, 48-67 µm broad.
Emended diagnosis: Sarjeant, 1966, p. 116
A Gonyaulacysta with spheroidal to ovoidal theca surmounted by blunt apical horn. Epitract longer than hypotract; antapex flattened. Tabulation: 4", 1a, 6"", 6c, 6""", 1p, ?1 p.v., 1""""; plates bordered by denticulate crests, varying considerably both in height and character of denticulation. Cingulum strongly spiral: sulcus sigmoidal, plates 6""" and 1""" roughly L-shaped. Surface bearing irregular scatter of tubercles.
Emended descrpition: Sarjeant, 1966, p. 117
The shell shape varies from an ovoid to an oblate spheroid; the length of the horn and the height and form of the crests are also very variable.
Of the four apical plates, plate I" occupies the anterior prolongation of the sulcus: it is long and narrow. An elongate anterior intercalary plate is present alongside it. The four apical plates together form the apical horn, their crests being confluent at its tip. Six precingular plates are present, with plate 6" small, elongate, and roughly L-shaped. Six post-equatorial plates are present, plate I"" being roughly axeshaped, with broad anterior and narrow posterior portions. A quadrate posterior intercalary plate is present. The single antapical plate is large and polygonal; the crests surrounding it are supported at their junctions by spines. A posterior ventral plate may be present, but if so, its anterior boundary is ill-defined.
The cingulum is relatively narrow and pronouncedly laevo-rotatory, its two ends differing in antero-posterior position by three times its width. The sulcus is darkedly sigmoidal; a median dorso-ventral section would thus cut both ends of the cingulum.
Six cingular plates appear to be present; the posterior end of the cingulum is separated from the sulcus by a small crescentic plate, poorly marked or indistinguishable in many specimens and thus excluded from the diagnosis. The crests crossing furrows lack denticles.
An irregular scatter of tubercles is present on the surfaces of the plates; the number, density and situation of these tubercles varies greatly between individuals.
A precingular archaeopyle is usually present, formed by loss of plate 3"".
Wrevittia helicoidea (Eisenack and Cookson, 1960, p.2–3, pl.1, figs.4–6,9 [figs.5-6 are now Wrevittia cassidata]) Helenes and Lucas-Clark, 1997, p.187.
Emendations: Sarjeant, 1966b, p.116, as Gonyaulacysta helicoidea; Helenes and Lucas-Clark, 1997, p.187–188, as Wrevittia helicoidea.
Holotype: Eisenack and Cookson, 1960, pl.1, fig.4; Jan du Chêne et al., 1986a, pl.40, figs.4–5.
Originally Gonyaulax (Appendix B), subsequently Gonyaulacysta, thirdly (and now) Wrevittia.
Taxonomic junior synonym: Gonyaulacysta (now Wrevittia?) diutina, according to Stover and Helby (1987d, p.287) -however, Jan du Chêne et al. (1986a, p.130) and Lentin and Williams (1989, p.152) retained Gonyaulacysta (now Wrevittia?) diutina.
Age: Neocomian–Aptian.
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Original description: Eisenackand Cookson, 1960, p.2
Shell broadly oval, unequally divided by a strongly helicoid girdle; epitheca longer than hypotheca, surmounded by a hollow, thin-walled conical projection with a blunt apex; hypotheca broadly rounded. Both the girdle and plates are bordered by relatively high ledges with serrate edges. The surface of the plates is ornamented to varying degrees with small irregularly scattered tubercles. The longitudinal furrow lies +/- obliquely to the long axis. A pylome may be developed by the removal of plate 3"".
Dimensions: Range: 62-86 µm long, 48-67 µm broad.
Emended diagnosis: Sarjeant, 1966, p. 116
A Gonyaulacysta with spheroidal to ovoidal theca surmounted by blunt apical horn. Epitract longer than hypotract; antapex flattened. Tabulation: 4", 1a, 6"", 6c, 6""", 1p, ?1 p.v., 1""""; plates bordered by denticulate crests, varying considerably both in height and character of denticulation. Cingulum strongly spiral: sulcus sigmoidal, plates 6""" and 1""" roughly L-shaped. Surface bearing irregular scatter of tubercles.
Emended descrpition: Sarjeant, 1966, p. 117
The shell shape varies from an ovoid to an oblate spheroid; the length of the horn and the height and form of the crests are also very variable.
Of the four apical plates, plate I" occupies the anterior prolongation of the sulcus: it is long and narrow. An elongate anterior intercalary plate is present alongside it. The four apical plates together form the apical horn, their crests being confluent at its tip. Six precingular plates are present, with plate 6" small, elongate, and roughly L-shaped. Six post-equatorial plates are present, plate I"" being roughly axeshaped, with broad anterior and narrow posterior portions. A quadrate posterior intercalary plate is present. The single antapical plate is large and polygonal; the crests surrounding it are supported at their junctions by spines. A posterior ventral plate may be present, but if so, its anterior boundary is ill-defined.
The cingulum is relatively narrow and pronouncedly laevo-rotatory, its two ends differing in antero-posterior position by three times its width. The sulcus is darkedly sigmoidal; a median dorso-ventral section would thus cut both ends of the cingulum.
Six cingular plates appear to be present; the posterior end of the cingulum is separated from the sulcus by a small crescentic plate, poorly marked or indistinguishable in many specimens and thus excluded from the diagnosis. The crests crossing furrows lack denticles.
An irregular scatter of tubercles is present on the surfaces of the plates; the number, density and situation of these tubercles varies greatly between individuals.
A precingular archaeopyle is usually present, formed by loss of plate 3"".