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Isabelidinium svartenhukense
Isabelidinium svartenhukense Nohr-Hansen 1996
Holotype: Nohr-Hansen 1996: Plate 3, Fig. 7
Paratype: Nohr-Hansen 1996: Plate 3, Fig. 11
Locus typicus: Core hole GGU 400712, Enclosure 8, Svartenhuk Halvo, West Greenland
Startum typicum: Late Cretaceous
Description: Nohr-Hansen 1996, p. 34, 35
Cyst type. Hypocavate-circumcavate, peridinioid. Shape. Dorso-ventrally compressed cyst, with an almost ovoidal to elongate quasi-pentagonal outline. The apical horn on the ovoidal specimens is reduced to a small bulge and the left antapical horn is very short whereas the right antapical horn is only a bulge. Specimens with a more elongate outline have a small blunt apical horn and a short left antapical horn. The right antapical horn is very short or more commonly appears as a bulge. Both forms have a spherical endocyst. Wall relationship. The cyst is composed of a smooth to scabrate, hyaline pericyst and a hyaline endocyst. The endophragm approaches the periphragm at the equator or just above and the two wall layers are parallel, with a very narrow epipericoel (1-3Á), up to the apical part of the cyst where the epipericoel can extend up to 10,uforming an apical horn or bulge. The hypopericoel on the ovoidal forms is smaller than on the more elongate forms. Tabulation. Paratabulation is only indicated by the archeopyle and the cingulum, when present. Cingulum is most common on the elongate forms, where its anterior and posterior margins are bordered by ridges with small granulae. On the ovoidal specimens a very weak tabulation pattern and cingulum outline is occasionally indicated by rows of granulae. Archeopyle. Intercalary (2a) thetaform archeopyle. Operculum often attached at posterior margin. It has not been possible to observe the endoarcheopyle.
Dimensions. Holotype: length of pericyst 65Á, width of pericyst 58Á, length of endocyst 45Á Paratype: length of pericyst 93Á, width of pericyst 65Á, length of endocyst 54Á. Size range. Ovoidal forms (10 specimens) length of pericyst 60 (71) 83Á, width of pericyst 45 (55) 63Á, length of epicyst 45 (52) 61Á. Elongate forms (14 specimens) length of pericyst 74 (82) 93Á, width of pericyst 43 (56) 65Á, length of epicyst 43 (52) 60Á.
Discussion: Nohr-Hansen 1996, p. 34, 35
The shape of the pericyst, endocyst and very narrow epipericoel distinguish the new species Isabelidinium svartenhukense from most other Isabelidinium species. 1. svartenhukense is very similar in shape to I. variabile Marshall (1988), especially the informally described subspecies A and D (Marshall, 1988, p. 207, 211). However I. variabile differs by having a periphragm with closely spaced perforations and a scabrate, granulate or verrucate endophragm. The species Eurydinium glomeratum (Davey, 1970) Stover & Evitt 1978, is dis- tinguished from I. svartenhukense by having a much smaller hypopericoel and by having an endocyst that is in contact with the periphragm except in the apical and antapical regions.
Occurrence. The species has been recorded from the Coniacian and early Santonian Arvalidium scheii, Laciniadinium arcticum and Heterosphaeridium difficile intervals on Svartenhuk (Enclosures 1,8,10,11). The ovoidal form is most common in the A. scheii interval, whereas the elongate form first occurs in the top of the A. scheii interval. The somewhat similar species i. varabile has been described from the Santonian in southern Australia by Marshall (1988) and later recorded from the late Santonian to the late Campanian in the same area (Marshall, 1990).
Holotype: Nohr-Hansen 1996: Plate 3, Fig. 7
Paratype: Nohr-Hansen 1996: Plate 3, Fig. 11
Locus typicus: Core hole GGU 400712, Enclosure 8, Svartenhuk Halvo, West Greenland
Startum typicum: Late Cretaceous
Description: Nohr-Hansen 1996, p. 34, 35
Cyst type. Hypocavate-circumcavate, peridinioid. Shape. Dorso-ventrally compressed cyst, with an almost ovoidal to elongate quasi-pentagonal outline. The apical horn on the ovoidal specimens is reduced to a small bulge and the left antapical horn is very short whereas the right antapical horn is only a bulge. Specimens with a more elongate outline have a small blunt apical horn and a short left antapical horn. The right antapical horn is very short or more commonly appears as a bulge. Both forms have a spherical endocyst. Wall relationship. The cyst is composed of a smooth to scabrate, hyaline pericyst and a hyaline endocyst. The endophragm approaches the periphragm at the equator or just above and the two wall layers are parallel, with a very narrow epipericoel (1-3Á), up to the apical part of the cyst where the epipericoel can extend up to 10,uforming an apical horn or bulge. The hypopericoel on the ovoidal forms is smaller than on the more elongate forms. Tabulation. Paratabulation is only indicated by the archeopyle and the cingulum, when present. Cingulum is most common on the elongate forms, where its anterior and posterior margins are bordered by ridges with small granulae. On the ovoidal specimens a very weak tabulation pattern and cingulum outline is occasionally indicated by rows of granulae. Archeopyle. Intercalary (2a) thetaform archeopyle. Operculum often attached at posterior margin. It has not been possible to observe the endoarcheopyle.
Dimensions. Holotype: length of pericyst 65Á, width of pericyst 58Á, length of endocyst 45Á Paratype: length of pericyst 93Á, width of pericyst 65Á, length of endocyst 54Á. Size range. Ovoidal forms (10 specimens) length of pericyst 60 (71) 83Á, width of pericyst 45 (55) 63Á, length of epicyst 45 (52) 61Á. Elongate forms (14 specimens) length of pericyst 74 (82) 93Á, width of pericyst 43 (56) 65Á, length of epicyst 43 (52) 60Á.
Discussion: Nohr-Hansen 1996, p. 34, 35
The shape of the pericyst, endocyst and very narrow epipericoel distinguish the new species Isabelidinium svartenhukense from most other Isabelidinium species. 1. svartenhukense is very similar in shape to I. variabile Marshall (1988), especially the informally described subspecies A and D (Marshall, 1988, p. 207, 211). However I. variabile differs by having a periphragm with closely spaced perforations and a scabrate, granulate or verrucate endophragm. The species Eurydinium glomeratum (Davey, 1970) Stover & Evitt 1978, is dis- tinguished from I. svartenhukense by having a much smaller hypopericoel and by having an endocyst that is in contact with the periphragm except in the apical and antapical regions.
Occurrence. The species has been recorded from the Coniacian and early Santonian Arvalidium scheii, Laciniadinium arcticum and Heterosphaeridium difficile intervals on Svartenhuk (Enclosures 1,8,10,11). The ovoidal form is most common in the A. scheii interval, whereas the elongate form first occurs in the top of the A. scheii interval. The somewhat similar species i. varabile has been described from the Santonian in southern Australia by Marshall (1988) and later recorded from the late Santonian to the late Campanian in the same area (Marshall, 1990).