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Gonyaulacysta australica
Original description: [Cookson and Eisenack, 1982] (translated from German):
Psaligonyaulax australica n. sp.
Plate 2, Figs. 13-15
Type: The specimen shown on Plate 2, Fig. 14, preserved in specimen Cape Range No. 2.
Locus typicus and stratum typicum: Cape Range. Dingo Claystone (upper portion), Wapet's Well No. 2 between 3970 and 3991 ft. Oxfordian to Lower Kimeridgian. Exmouth Gulf area of Carnarvon Basin, Western Australia.
Diagnosis: A Psaligonyaulax that closely resembles Ps. apatela, but differs in that the antapical appendage, which in Ps. apatela is developed as a four-sided appendage, is either only vaguely present or completely absent in Ps. australica, so that Ps. australica then has a rounded antapical end. The periphragm is thin, the surface smooth. No wainscoting is discernible. The endophragm is also thin-walled and delicate, often difficult to identify. The apical projection, which is usually distinct in Ps. apatela, is also present, but not always distinct.
The apical horn, as in Ps. apatela, is well defined; it is cylindrical to slightly conical and blunt at the end.
The archaeopyle is horseshoe-shaped and sometimes very elongated; it extends from the girdle region almost to the base of the apical horn.
Dimensions: Holotype: approx. 140 x 76 μ long, the remaining specimens measure approx. 109 x 6 μ, 114 x 78 μ, and 128 x 76 μ.
Relationships: Ps. australica is very similar to Psaligonyanlax sp., briefly described by GrTMEZ 1970, p. 304, and illustrated in Plate 3, Fig. 6, and in text fig. 30, except that it is smaller at 70 μ long.
There is also a similarity to "Gonyaulacysta jurassica" in Pocock (1972, p. 197; pl. 22 Fig. 9), which is certainly not G. jurasica: Both forms share the same overall outline.
Our species differs from Gonyaulacysta jurassica in its more slender form, the absence of plating, and the serrations on the lateral margins.
Occurrence: See above under Locus typicus.
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Emended description Riding et al., 2022:
Emended diagnosis: A large, bicavate, smooth-walled species of Gonyaulacystawith a relatively short apical horn formed of periphragm. The cyst outline is subovoidal to subquadrangular, with a rounded, almost semicircular, hypocyst. The sutural features are low, smooth crests or ridges, which may be perforate and/or bear tiny denticles. The sulcus is longitudinal L-type.
Emended description: A large, subovoidal/subquadrangular species of Gonyaulacysta with bicavate wall structure. The antapical region is markedly rounded and approaches a semicircle in outline. Its shape varies from noticeably elongate to somewhat squat. The epipericoel and hypopericoel are not extensive. The species has a relatively short, subtriangular apical horn comprised of periphragm, which is truncate distally. The endocyst may or may not exhibit a rounded apical protuberance. The tabulation is marked by sutural crests or ridges that are distally smooth or may bear tiny denticles. The L-type sulcus is longitudinal. The crests or ridges are usually low and can be perforate. A small opisthopyle may be observable. Both the endophragm and periphragm are smooth.
Holotype: Specimen P. 47281 of Cookson and Eisenack (1982, pl. 2, 14). Sample from sample C.R.A., C.R. 69 from the upper part of the Dingo Claystone (Oxfordian to lower Kimmeridgian) between 1217 m and 1210min the Cape Range No. 2 Borehole, Exmouth Gulf, Carnarvon Basin, Western Australia. Curated at Museum Victoria, Melbourne, Australia.
Comments: Gonyaulacysta australica has not been recorded since its initial description, and hence it appears not be a significant index fossil in Australasia. It is emended herein to provide a modern and comprehensive guide to its morphology. This species is bicavate and is characterised by a small apical horn, dominantly smooth sutural crests or ridges, and a rounded, virtually semicircular, hypocyst. The species was considered a taxonomic junior synonym of Gonyaulacysta dualis by Brenner (1988) and of Scriniodinium? (now Gonyaulacysta) ceratophorum by Jan du Chêne et al. (1986). It is close in morphology to Gonyaulacysta ceratophora, however,we choose to retain both as separate species. This is because Gonyaulacysta australica, unlike Gonyaulacysta ceratophora, has a well-rounded ambitus and a moderately large apical horn; it also entirely lacks distinctive ornament on the sutural crests.
Comparison: The most similar species to Gonyaulacysta australica is Gonyaulacysta dualis. However, the latter is subpentagonal in overall shape, has a prominent apical horn, and both the epipericoel and hypopericoel are well developed.
Dimensions: According to Cookson and Eisenack (1982, p. 37), the size of the holotype of Gonyaulacysta australica is 140 × 76 μm. The dimensions of other specimens are 128 × 76 μm, 114 × 78 μm and 109 × 60 μm.
Geographical and stratigraphical distribution: Gonyaulacysta australica was reported from the Oxfordian and Kimmeridgian of Western Australia by Cookson and Eisenack (1982).
Psaligonyaulax australica n. sp.
Plate 2, Figs. 13-15
Type: The specimen shown on Plate 2, Fig. 14, preserved in specimen Cape Range No. 2.
Locus typicus and stratum typicum: Cape Range. Dingo Claystone (upper portion), Wapet's Well No. 2 between 3970 and 3991 ft. Oxfordian to Lower Kimeridgian. Exmouth Gulf area of Carnarvon Basin, Western Australia.
Diagnosis: A Psaligonyaulax that closely resembles Ps. apatela, but differs in that the antapical appendage, which in Ps. apatela is developed as a four-sided appendage, is either only vaguely present or completely absent in Ps. australica, so that Ps. australica then has a rounded antapical end. The periphragm is thin, the surface smooth. No wainscoting is discernible. The endophragm is also thin-walled and delicate, often difficult to identify. The apical projection, which is usually distinct in Ps. apatela, is also present, but not always distinct.
The apical horn, as in Ps. apatela, is well defined; it is cylindrical to slightly conical and blunt at the end.
The archaeopyle is horseshoe-shaped and sometimes very elongated; it extends from the girdle region almost to the base of the apical horn.
Dimensions: Holotype: approx. 140 x 76 μ long, the remaining specimens measure approx. 109 x 6 μ, 114 x 78 μ, and 128 x 76 μ.
Relationships: Ps. australica is very similar to Psaligonyanlax sp., briefly described by GrTMEZ 1970, p. 304, and illustrated in Plate 3, Fig. 6, and in text fig. 30, except that it is smaller at 70 μ long.
There is also a similarity to "Gonyaulacysta jurassica" in Pocock (1972, p. 197; pl. 22 Fig. 9), which is certainly not G. jurasica: Both forms share the same overall outline.
Our species differs from Gonyaulacysta jurassica in its more slender form, the absence of plating, and the serrations on the lateral margins.
Occurrence: See above under Locus typicus.
------------------------------------------------------------------------------
Emended description Riding et al., 2022:
Emended diagnosis: A large, bicavate, smooth-walled species of Gonyaulacystawith a relatively short apical horn formed of periphragm. The cyst outline is subovoidal to subquadrangular, with a rounded, almost semicircular, hypocyst. The sutural features are low, smooth crests or ridges, which may be perforate and/or bear tiny denticles. The sulcus is longitudinal L-type.
Emended description: A large, subovoidal/subquadrangular species of Gonyaulacysta with bicavate wall structure. The antapical region is markedly rounded and approaches a semicircle in outline. Its shape varies from noticeably elongate to somewhat squat. The epipericoel and hypopericoel are not extensive. The species has a relatively short, subtriangular apical horn comprised of periphragm, which is truncate distally. The endocyst may or may not exhibit a rounded apical protuberance. The tabulation is marked by sutural crests or ridges that are distally smooth or may bear tiny denticles. The L-type sulcus is longitudinal. The crests or ridges are usually low and can be perforate. A small opisthopyle may be observable. Both the endophragm and periphragm are smooth.
Holotype: Specimen P. 47281 of Cookson and Eisenack (1982, pl. 2, 14). Sample from sample C.R.A., C.R. 69 from the upper part of the Dingo Claystone (Oxfordian to lower Kimmeridgian) between 1217 m and 1210min the Cape Range No. 2 Borehole, Exmouth Gulf, Carnarvon Basin, Western Australia. Curated at Museum Victoria, Melbourne, Australia.
Comments: Gonyaulacysta australica has not been recorded since its initial description, and hence it appears not be a significant index fossil in Australasia. It is emended herein to provide a modern and comprehensive guide to its morphology. This species is bicavate and is characterised by a small apical horn, dominantly smooth sutural crests or ridges, and a rounded, virtually semicircular, hypocyst. The species was considered a taxonomic junior synonym of Gonyaulacysta dualis by Brenner (1988) and of Scriniodinium? (now Gonyaulacysta) ceratophorum by Jan du Chêne et al. (1986). It is close in morphology to Gonyaulacysta ceratophora, however,we choose to retain both as separate species. This is because Gonyaulacysta australica, unlike Gonyaulacysta ceratophora, has a well-rounded ambitus and a moderately large apical horn; it also entirely lacks distinctive ornament on the sutural crests.
Comparison: The most similar species to Gonyaulacysta australica is Gonyaulacysta dualis. However, the latter is subpentagonal in overall shape, has a prominent apical horn, and both the epipericoel and hypopericoel are well developed.
Dimensions: According to Cookson and Eisenack (1982, p. 37), the size of the holotype of Gonyaulacysta australica is 140 × 76 μm. The dimensions of other specimens are 128 × 76 μm, 114 × 78 μm and 109 × 60 μm.
Geographical and stratigraphical distribution: Gonyaulacysta australica was reported from the Oxfordian and Kimmeridgian of Western Australia by Cookson and Eisenack (1982).