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Rhaetogonyaulax wigginsii
Rhaetogonyaulax wigginsii (Stover and Helby, 1987) Lentin and Williams, 1989
Originally Shublikodinium, subsequently (and now) Rhaetogonyaulax.
Holotype: Stover and Helby, 1987, fig.19A-B
Paratypes: Stover and Helby, 1987
Locus typicus: Bonaparte Basin, Australia
Stratum typicum: Late Carnian
Original description: Stover and Helby, 1987, p. 120: Shublikodinium wigginsii
Cysts proximate, biconical with a low pyramidal apical horn and a rounded antapex, whose outline may be interrupted by 2, generally short protuberences; left protuberence usually more prominent than right and commonly with a short pointed horn. Autophragm about 1µm thick (exclusive of sculptural elements), and bears parasutural and intratabular, solid, often distally expanded processes (up to 4 µm long, 0.5-1 µm diameter), scattered grana (up to 0.5 µm diameter), or is shagreenate. Parasutural ridges up to 3 µm high and 1.5 µm wide developed along anterior and posterior margins of paracingulum, and slightly lower along the hypocystal margin of parasulcus. Ridges characteristically surmounted by projections higher than those on the surface of paraplates or along other parasutural margins. Paratabulation incompletely expressed by archeopyle, accessory archeopyle sutures and faint parasutural alignment of projections. Despite paratabulation of the epicyst being interpreted as Xpr, 6", 5a, 7", as (Fig.18A,B) definition of plate boundaries commonly obscure. Paratabulation on hypocyst even more obscure than on epicyst although a small triangular paraplate bounded by prominent ridges frequently at the antapex (Figs 19H, 20). Archeopyle intercalary, type I to 5I.
Paracingulum broad, often up to 10 µm at its widest point, strongly indented, and apparently undivided; margined by strongly developed ridges surmounted by baculate projections. Parasulcus clearly defined on the hypocyst by a bounding ridge, outlining a broad, indented area; its extension onto the epicyst less evident. Specimens 43-76 µm long and 33-65 µm wide. Variability. Within individual samples there is considerable variation in ornamentation styles. These vary from specimens with a shagreenate autophragm having very low cingular ridges and lacking projections to specimens with prominent sulcal and cingular ridges surmounted by moderately large projections and also possessing intratabular features and polar concentrations of projections. The nature of the archeopyle is extremely variable. Of 700 specimens recorded, 50% had lost 1-5 intercalary paraplates, 32% had lost both the intercalary and the apical paraplate series, 10% retained all paraplates. Rare specimens had lost some intercalary and I or 2 apical paraplates. There appears to be no consistent pattern in the loss of apical paraplates.
Affinities:
Stover and Helby, 1987, p. 120: Shublikodinium wigginsii
Shublikodinium wigginsii is distinguished from S. arcticum Wiggins 1973 and its variants by having prominent processes on the ridges which mark the paracingulum and posterior parasulcus, lower length/width ratio, and very broad and well-defined posterior parasulcus (although several of Wiggins"s specimens also show this feature). The triangular ridged field at the antapex (Figs 19H,20) appears to be unique in S. wigginsii. Shublikodinium verrucosum Wiggins 1973 is more elongate and has a relatively narrow posterior parasulcus. That style of Shublikodinium occurs in Norian strata in Australia.
Originally Shublikodinium, subsequently (and now) Rhaetogonyaulax.
Holotype: Stover and Helby, 1987, fig.19A-B
Paratypes: Stover and Helby, 1987
Locus typicus: Bonaparte Basin, Australia
Stratum typicum: Late Carnian
Original description: Stover and Helby, 1987, p. 120: Shublikodinium wigginsii
Cysts proximate, biconical with a low pyramidal apical horn and a rounded antapex, whose outline may be interrupted by 2, generally short protuberences; left protuberence usually more prominent than right and commonly with a short pointed horn. Autophragm about 1µm thick (exclusive of sculptural elements), and bears parasutural and intratabular, solid, often distally expanded processes (up to 4 µm long, 0.5-1 µm diameter), scattered grana (up to 0.5 µm diameter), or is shagreenate. Parasutural ridges up to 3 µm high and 1.5 µm wide developed along anterior and posterior margins of paracingulum, and slightly lower along the hypocystal margin of parasulcus. Ridges characteristically surmounted by projections higher than those on the surface of paraplates or along other parasutural margins. Paratabulation incompletely expressed by archeopyle, accessory archeopyle sutures and faint parasutural alignment of projections. Despite paratabulation of the epicyst being interpreted as Xpr, 6", 5a, 7", as (Fig.18A,B) definition of plate boundaries commonly obscure. Paratabulation on hypocyst even more obscure than on epicyst although a small triangular paraplate bounded by prominent ridges frequently at the antapex (Figs 19H, 20). Archeopyle intercalary, type I to 5I.
Paracingulum broad, often up to 10 µm at its widest point, strongly indented, and apparently undivided; margined by strongly developed ridges surmounted by baculate projections. Parasulcus clearly defined on the hypocyst by a bounding ridge, outlining a broad, indented area; its extension onto the epicyst less evident. Specimens 43-76 µm long and 33-65 µm wide. Variability. Within individual samples there is considerable variation in ornamentation styles. These vary from specimens with a shagreenate autophragm having very low cingular ridges and lacking projections to specimens with prominent sulcal and cingular ridges surmounted by moderately large projections and also possessing intratabular features and polar concentrations of projections. The nature of the archeopyle is extremely variable. Of 700 specimens recorded, 50% had lost 1-5 intercalary paraplates, 32% had lost both the intercalary and the apical paraplate series, 10% retained all paraplates. Rare specimens had lost some intercalary and I or 2 apical paraplates. There appears to be no consistent pattern in the loss of apical paraplates.
Affinities:
Stover and Helby, 1987, p. 120: Shublikodinium wigginsii
Shublikodinium wigginsii is distinguished from S. arcticum Wiggins 1973 and its variants by having prominent processes on the ridges which mark the paracingulum and posterior parasulcus, lower length/width ratio, and very broad and well-defined posterior parasulcus (although several of Wiggins"s specimens also show this feature). The triangular ridged field at the antapex (Figs 19H,20) appears to be unique in S. wigginsii. Shublikodinium verrucosum Wiggins 1973 is more elongate and has a relatively narrow posterior parasulcus. That style of Shublikodinium occurs in Norian strata in Australia.