Back
Impagidinium setcheyense
From Fensome et al., 2019:
Impagidinium setcheyense (Sarjeant, 1976c, p.4–6, pl.1, fig.7; text-fig.1) Courtinat, 1989, p.205. Holotype: Sarjeant, 1976c, pl.1,
fig.7; Jan du Chêne et al., 1986a, pl.74, figs.1–4. Originally Gonyaulacysta, subsequently Leptodinium, thirdly Rhynchodiniopsis, fourthly (and now) Impagidinium. Age: Kimmeridgian.
---------------------------------------------------------------------------------------------------
Original description: [Sarjeant, 1976c]:
Gonyanacysta setcheyensis sp. nov.
Plate 1, figure 7; Text-figure 1
Palaeoperidinium hyalodermum Deflandre; Downie, 1957, p. 422, PI. 20, fig. 9.
Gonyanlacysta cf. helicoidea Eisenack & Cookson; Gitmez, 1970, PI. 2, fig. 1, 2, Text-fig. 11; Gitmez and Sarjeant, 1972, Table 3, 5, 6; Riley and Sarjeant, 1972, Table 3, 4.
Gonyanlacysta hyaloderma (Deflandre); Gitmez, 1970, p. 259; Gitmez and Sarjeant, 1972, Table 3, 5.
Etymology: After the type locality, Setchey, Norfolk.
Diagnosis: A species of Gonyaulacysta of moderate size, with a rounded-pentagonal ambitus. Epitract conical and topped by a blunt apical horn, hypotract in the shape of a truncated cone. Plate-area boundaries marked by crests of variable but usually moderate height; abulation 4', 1a, 6", 6c, 6'", 1pv, 1"", plus at least three sulcal plate areas and possibly a pre-apical plate area on the tip of the horn. Cingulum helicoid, laevorotatory, its two ends differing in anteroposterior position by approximately the cingulum's breadth; sulcus slightly sigmoid, so that the dorsoventral plane through the cyst would touch and almost, but not quite, intersect the two ends of the cingulum. Outer margins of crests smooth, shallowly scalloped or denticulate. Surface of cyst irregularly tuberculate.
Holotype: Specimen ML27, Micropalaeontelogy Laboratory, Department of Geology, University of Sheffield, England.
Type horizon and locality: Kimeridge Clay, Jurassic (Kimmeridgian: Hudlestoni Zone), Setchey, Norfolk.
Description: Tract typically rounded-polygonal, but varying between markedly polygonal and almost ovoidal. Apical horn consistently present, but sometimes very short. The presence of a preapical plate area occupying 1ts tip was presumed because of the flattened shape of the tip, but could not be confirmed.
Four apical plate areas present; plate area 1' elongate and situated in anterior prolongation of sulcus; other three apical plate areas polygonal and of more or less equal size.
Six precingular plate areas present; plate area 6" reduced to accommodate anterior intercalary plate area and with tongue-like ventral extension at intersection of cingulum and sulcus. Plate area 3" is lost in archeopyle formation.
Cingulum relatively narrow, but broadens at its left intersection with sulcus; plate area 1c small and elongate in anteroposterior direction. The other cingular plate areas are laterally elongate and of more or less equal size, though plate area 6c exhibits a sulcus-ward prolongation on its posterior side. The unusual shapes of plate areas 6" and 6c result from mid-ventral torsion of the sulcus, which is divided into at least three plate areas (anterior, mid and posterior sulcals) of which the first is the largest. Posterior sulcal plate separated from antapex by a posterior ventral plate area, slightly larger in size and widening posteriorly.
Plate area 1"' is the smallest of the six postcingular plate areas and is anteroposteriorly elongate. Plate area 2'" asymmetrically quadrilateral, with long anterior and left lateral sides and short ventral and posterior sides. A posterior intercalary plate area separates plate areas 1'" and 2'" from the antapex; the antapical plate area is relatively large.
The crests bounding the plate areas are sometimes little more than low ridges; but in other specimens they are of moderate height, with edges showing shallow scallops or bearing widely to closely spaced denticles of variable height. No specimens with high crests were seen.
Surface of periphragm laevigate, minutely granular or punctate. It shows an irregular scatter of tubercles, so varied in size, number, and distribution in each individual seen that no generalizations can be made. Endophragm and periphragm in general contact, but crests and apical horn formed from periphragm only.
Dimensions: Holotype, overall length 42 pm, overall breadth 35 Lm, length of apical horn 6 pm, height of crests 1 um-1.5 um. Range of dimensions -overall length 38 um -50 um, overall breadth 30 pm-45 um. Number of specimens examined, 22.
Discussion: Small proximate cysts that show a general resemblance to the Upper Jurassic Gonyaulacysta jurassica (Deflandre) and the Lower Cretaceous G. cretacea (Neale and Sarjeant) and G. belicoidea (Eisenack and Cookson) are present in low numbers in many Kimmeridgian assemblages from England and northern France. Because of their infrequency and their variable morphology, no new name has hitherto been proposed for them.
Downie (1957) originally attributed the form that he encountered to Deflandre's species Palaeoperidinium hyaloder mum. Gitmez (1970) quite justifiably compared the single specimen she encountered with the Cretaceous species Gonyaulacy sta helicoidea (of which G. Cretacea may well be a junior synonym), on the basis of the torsion of the sulcus; she noted that there were differences between the Kimmeridgian forms and typical G. belicoidea, but did not specify these differences in any detail. Downie's specimen was placed by her into the synonymy of G. byaloderma (ex: Palaeoperidıniu mn byalodermu m), for which an emended diagnosis was proposed.
The Kimmeridgian forms here described exhibit differences in morphology fromn both species to which they have hitherto been attributed. Gonyanlacysta hyaloderma has a more markedly ovoidal ambitus; its cingulum is broader and its sulcus appears to show no torsion; the apical horn is very short indeed, and the ventral tabulation appears to be much simpler (although a restudy of the holotype is necessary to
confirm this). The two Cretaceous species, in contrast, exhibit a much higher degree of sulcal torsion, so that a dorsoventral plane through the cyst would unquestionably intersect the two ends of the cingulum; their ventral tabulation is dissimilar in detail of plate shape from that of G. setcheyensis. The abundant Jurassic species G. jurassica (also present in the lowest Kimmeridgian assemblages) is usually somewhat larger, but of similar mnorphology, showing great variation in horn length and crest height; however, it consistently shows no sulcal torsion and, in con-
sequence, the shapes of the plates adjoining the intersection of cingulumn and sulcus are markedly different.
It is quite possible that this new species represents an intermediate morphological stage between G. jurassica and the G. cretacea/G. helicoidea complex; in other words, that G. setcheyensis forms a part of the same evolutionary lineage. However, the morphological differences from typical representatives of those species are considered sufficient to justify a new name. Like those species, G. setcheyensis exhibits considerable variation in horn length and crest height; like G. belicoidea, its surface may bear variable numbers of tubercles, of very variable
breadth and height, some almost like warts, others approaching the character of spinelets.
Downie's specimen was chosen as holotype in part for historical reasons and in part because, despite the organic debris surrounding it, it exhibits the dorsal and ventral tabulation particularly clearly.
A reexamination of the specimen illustrated by Gitmez (1970, P1. 2, fig. 1, 2, Text-fig. 11; BM NH slide V.53931]) indicated the presence of the
small plate area 1c and 1"'; her plate area 1"' is thus plate area 2"', The boundary that she illustrates between plate areas 2"' and 3"' seems in fact to be a fold; these two "plates" together constitute plate area 3"' and her plate areas 4"'-6"' thus are correctly numbered. I must also now disagree with her interpretation of the cingular plate areas; her plate areas 1c to 5c should be renumbered 2c to 6c, because she did not recognize the small plate area 1c and because the supposed boundary between her plate areas 5c and 6c again appears to be a fold. The
specimen is obliquely positioned and would not make a suitable holotype; and, although some 20 further specimens examined could be confidently assigned to this new species, all were too unfavorably preserved or positioned to be suitable as types.
Known stratigrapbical range: Upper Jurassic (Kimmeridgian: Baylei to Pectinatus zones), England and France.
------------------------------------------------------------------------------------------------------------------------------------------------------
Translation Courtinat, 1989: LPP
Remark: Courtinat, 1989, p.205
The sulcus presents an S-type organisation; in the ventral area the arrangement is type A/ai. These two characteristics correspond to the genus Impagidinium.
Impagidinium setcheyense (Sarjeant, 1976c, p.4–6, pl.1, fig.7; text-fig.1) Courtinat, 1989, p.205. Holotype: Sarjeant, 1976c, pl.1,
fig.7; Jan du Chêne et al., 1986a, pl.74, figs.1–4. Originally Gonyaulacysta, subsequently Leptodinium, thirdly Rhynchodiniopsis, fourthly (and now) Impagidinium. Age: Kimmeridgian.
---------------------------------------------------------------------------------------------------
Original description: [Sarjeant, 1976c]:
Gonyanacysta setcheyensis sp. nov.
Plate 1, figure 7; Text-figure 1
Palaeoperidinium hyalodermum Deflandre; Downie, 1957, p. 422, PI. 20, fig. 9.
Gonyanlacysta cf. helicoidea Eisenack & Cookson; Gitmez, 1970, PI. 2, fig. 1, 2, Text-fig. 11; Gitmez and Sarjeant, 1972, Table 3, 5, 6; Riley and Sarjeant, 1972, Table 3, 4.
Gonyanlacysta hyaloderma (Deflandre); Gitmez, 1970, p. 259; Gitmez and Sarjeant, 1972, Table 3, 5.
Etymology: After the type locality, Setchey, Norfolk.
Diagnosis: A species of Gonyaulacysta of moderate size, with a rounded-pentagonal ambitus. Epitract conical and topped by a blunt apical horn, hypotract in the shape of a truncated cone. Plate-area boundaries marked by crests of variable but usually moderate height; abulation 4', 1a, 6", 6c, 6'", 1pv, 1"", plus at least three sulcal plate areas and possibly a pre-apical plate area on the tip of the horn. Cingulum helicoid, laevorotatory, its two ends differing in anteroposterior position by approximately the cingulum's breadth; sulcus slightly sigmoid, so that the dorsoventral plane through the cyst would touch and almost, but not quite, intersect the two ends of the cingulum. Outer margins of crests smooth, shallowly scalloped or denticulate. Surface of cyst irregularly tuberculate.
Holotype: Specimen ML27, Micropalaeontelogy Laboratory, Department of Geology, University of Sheffield, England.
Type horizon and locality: Kimeridge Clay, Jurassic (Kimmeridgian: Hudlestoni Zone), Setchey, Norfolk.
Description: Tract typically rounded-polygonal, but varying between markedly polygonal and almost ovoidal. Apical horn consistently present, but sometimes very short. The presence of a preapical plate area occupying 1ts tip was presumed because of the flattened shape of the tip, but could not be confirmed.
Four apical plate areas present; plate area 1' elongate and situated in anterior prolongation of sulcus; other three apical plate areas polygonal and of more or less equal size.
Six precingular plate areas present; plate area 6" reduced to accommodate anterior intercalary plate area and with tongue-like ventral extension at intersection of cingulum and sulcus. Plate area 3" is lost in archeopyle formation.
Cingulum relatively narrow, but broadens at its left intersection with sulcus; plate area 1c small and elongate in anteroposterior direction. The other cingular plate areas are laterally elongate and of more or less equal size, though plate area 6c exhibits a sulcus-ward prolongation on its posterior side. The unusual shapes of plate areas 6" and 6c result from mid-ventral torsion of the sulcus, which is divided into at least three plate areas (anterior, mid and posterior sulcals) of which the first is the largest. Posterior sulcal plate separated from antapex by a posterior ventral plate area, slightly larger in size and widening posteriorly.
Plate area 1"' is the smallest of the six postcingular plate areas and is anteroposteriorly elongate. Plate area 2'" asymmetrically quadrilateral, with long anterior and left lateral sides and short ventral and posterior sides. A posterior intercalary plate area separates plate areas 1'" and 2'" from the antapex; the antapical plate area is relatively large.
The crests bounding the plate areas are sometimes little more than low ridges; but in other specimens they are of moderate height, with edges showing shallow scallops or bearing widely to closely spaced denticles of variable height. No specimens with high crests were seen.
Surface of periphragm laevigate, minutely granular or punctate. It shows an irregular scatter of tubercles, so varied in size, number, and distribution in each individual seen that no generalizations can be made. Endophragm and periphragm in general contact, but crests and apical horn formed from periphragm only.
Dimensions: Holotype, overall length 42 pm, overall breadth 35 Lm, length of apical horn 6 pm, height of crests 1 um-1.5 um. Range of dimensions -overall length 38 um -50 um, overall breadth 30 pm-45 um. Number of specimens examined, 22.
Discussion: Small proximate cysts that show a general resemblance to the Upper Jurassic Gonyaulacysta jurassica (Deflandre) and the Lower Cretaceous G. cretacea (Neale and Sarjeant) and G. belicoidea (Eisenack and Cookson) are present in low numbers in many Kimmeridgian assemblages from England and northern France. Because of their infrequency and their variable morphology, no new name has hitherto been proposed for them.
Downie (1957) originally attributed the form that he encountered to Deflandre's species Palaeoperidinium hyaloder mum. Gitmez (1970) quite justifiably compared the single specimen she encountered with the Cretaceous species Gonyaulacy sta helicoidea (of which G. Cretacea may well be a junior synonym), on the basis of the torsion of the sulcus; she noted that there were differences between the Kimmeridgian forms and typical G. belicoidea, but did not specify these differences in any detail. Downie's specimen was placed by her into the synonymy of G. byaloderma (ex: Palaeoperidıniu mn byalodermu m), for which an emended diagnosis was proposed.
The Kimmeridgian forms here described exhibit differences in morphology fromn both species to which they have hitherto been attributed. Gonyanlacysta hyaloderma has a more markedly ovoidal ambitus; its cingulum is broader and its sulcus appears to show no torsion; the apical horn is very short indeed, and the ventral tabulation appears to be much simpler (although a restudy of the holotype is necessary to
confirm this). The two Cretaceous species, in contrast, exhibit a much higher degree of sulcal torsion, so that a dorsoventral plane through the cyst would unquestionably intersect the two ends of the cingulum; their ventral tabulation is dissimilar in detail of plate shape from that of G. setcheyensis. The abundant Jurassic species G. jurassica (also present in the lowest Kimmeridgian assemblages) is usually somewhat larger, but of similar mnorphology, showing great variation in horn length and crest height; however, it consistently shows no sulcal torsion and, in con-
sequence, the shapes of the plates adjoining the intersection of cingulumn and sulcus are markedly different.
It is quite possible that this new species represents an intermediate morphological stage between G. jurassica and the G. cretacea/G. helicoidea complex; in other words, that G. setcheyensis forms a part of the same evolutionary lineage. However, the morphological differences from typical representatives of those species are considered sufficient to justify a new name. Like those species, G. setcheyensis exhibits considerable variation in horn length and crest height; like G. belicoidea, its surface may bear variable numbers of tubercles, of very variable
breadth and height, some almost like warts, others approaching the character of spinelets.
Downie's specimen was chosen as holotype in part for historical reasons and in part because, despite the organic debris surrounding it, it exhibits the dorsal and ventral tabulation particularly clearly.
A reexamination of the specimen illustrated by Gitmez (1970, P1. 2, fig. 1, 2, Text-fig. 11; BM NH slide V.53931]) indicated the presence of the
small plate area 1c and 1"'; her plate area 1"' is thus plate area 2"', The boundary that she illustrates between plate areas 2"' and 3"' seems in fact to be a fold; these two "plates" together constitute plate area 3"' and her plate areas 4"'-6"' thus are correctly numbered. I must also now disagree with her interpretation of the cingular plate areas; her plate areas 1c to 5c should be renumbered 2c to 6c, because she did not recognize the small plate area 1c and because the supposed boundary between her plate areas 5c and 6c again appears to be a fold. The
specimen is obliquely positioned and would not make a suitable holotype; and, although some 20 further specimens examined could be confidently assigned to this new species, all were too unfavorably preserved or positioned to be suitable as types.
Known stratigrapbical range: Upper Jurassic (Kimmeridgian: Baylei to Pectinatus zones), England and France.
------------------------------------------------------------------------------------------------------------------------------------------------------
Translation Courtinat, 1989: LPP
Remark: Courtinat, 1989, p.205
The sulcus presents an S-type organisation; in the ventral area the arrangement is type A/ai. These two characteristics correspond to the genus Impagidinium.