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Impagidinium phlyctaena
Impagidinium phlyctaena Stover and Helby, 1987
Holotype: Stover and Helby, 1987, fig.8A-H
Locus typicus: Perth Basin, W Australia
Stratum typicum: Barremian-Early Aptian
Original description: Stover and Helby, 1987, p. 268, 271
Cysts proximochorate, ellipsoidal, with appressed wall layers except where
parasutural folds and intratabular processes are developed. Periphragm smooth or very faintly textured. Precingular archeopyle reduced, formed by the release of paraplate 3"", operculum free. Gonyaulacacean paratabulation denoted by parasutural septa and folds, the latter surmounted by ridges. Parasutural features 7 Ám high at the gonal positions; intergonally they may be slightly to appreciably lower. Septa and ridges smooth to minutely perforate; their crests more or less straight to concave, with slightly uneven to somewhat ragged distal margins. Paratabulation formula: 4", 0a, 6", 6c, 5-6""", 1p, 1"""" ,1-5s. On the epicyst, the septa between paraplates 1" and 4 ", and between 6" and the parasulcus may be incompletely developed. On the hypocyst, paraplate 1""" quadrangular, narrow, and longitudinally elongate. However, the septum separating it from the parasulcus commonly poorly developed, or absent. Paraplate 1p delimited consistently. Most precingular and postcingular paraplates, especially those on the dorsal surface, and usually the antapical paraplate with an intratabular process, or 1, 2 or 3 relatively large granules. Processes hollow, conical, closed distally, or cylindrical and apparently open distally, about as high or lower than the septa. Paracingulum of 6 quadrangular and hexangular, transversely elongate paraplates; ends of the paracingulum offset markedly, with the distance between them being 2 to 3 times the width of the paracingulum. Parasulcus slightly sigmoid, widened posteriorly, and subdivided. Posterior sulcal paraplate delimited consistently, the anterior one occasionally, and 1 to 3 additional paraplates very rarely discernible and then only vaguely. A flagellar scar may be evident. Specimens range in length from 60-66Ám, and in width from 54-63Ám; 6 complete specimens measured.
Variability. Most of the variability is in the development of the parasutural features. On some specimens, only septa are present; on others septa and folds occur, and no specimen was found with folds only. The paraplates bordered by folds are usually, but not exclusively, those adjacent to the parasulcus and the paracingulum. On the fold bound paraplates, the dark marginal areas where the periphragm and endophragm are separated, stand in contrast to the lighter central areas where the two wall layers are in contact. This condition imposes a "window-pane" appearance on the paraplates and has been observed on other species of Impagidinium. It is characteristically developed on Carpodinium granulatum Cookson & Eisenack emend. Leffingwell & Morgan 1977. Some specimens of I. phlyctaena have a few, widely scattered, small granules in addition to the processes and large granules.
Affinities:
Stover and Helby, 1987, p. 271: Impagidinium phlyctaena is similar to Pterodinium premnon Duxbury 1980, which is described as having an intratabular projection on each paraplate. Impagidinium phlyctaena lacks intratabular features on the apical and cingular paraplates, and on some paraplates the features are large granules rather than processes. Because the ventral aspect of P. premnon was not illustrated, no further comparison is possible.
Holotype: Stover and Helby, 1987, fig.8A-H
Locus typicus: Perth Basin, W Australia
Stratum typicum: Barremian-Early Aptian
Original description: Stover and Helby, 1987, p. 268, 271
Cysts proximochorate, ellipsoidal, with appressed wall layers except where
parasutural folds and intratabular processes are developed. Periphragm smooth or very faintly textured. Precingular archeopyle reduced, formed by the release of paraplate 3"", operculum free. Gonyaulacacean paratabulation denoted by parasutural septa and folds, the latter surmounted by ridges. Parasutural features 7 Ám high at the gonal positions; intergonally they may be slightly to appreciably lower. Septa and ridges smooth to minutely perforate; their crests more or less straight to concave, with slightly uneven to somewhat ragged distal margins. Paratabulation formula: 4", 0a, 6", 6c, 5-6""", 1p, 1"""" ,1-5s. On the epicyst, the septa between paraplates 1" and 4 ", and between 6" and the parasulcus may be incompletely developed. On the hypocyst, paraplate 1""" quadrangular, narrow, and longitudinally elongate. However, the septum separating it from the parasulcus commonly poorly developed, or absent. Paraplate 1p delimited consistently. Most precingular and postcingular paraplates, especially those on the dorsal surface, and usually the antapical paraplate with an intratabular process, or 1, 2 or 3 relatively large granules. Processes hollow, conical, closed distally, or cylindrical and apparently open distally, about as high or lower than the septa. Paracingulum of 6 quadrangular and hexangular, transversely elongate paraplates; ends of the paracingulum offset markedly, with the distance between them being 2 to 3 times the width of the paracingulum. Parasulcus slightly sigmoid, widened posteriorly, and subdivided. Posterior sulcal paraplate delimited consistently, the anterior one occasionally, and 1 to 3 additional paraplates very rarely discernible and then only vaguely. A flagellar scar may be evident. Specimens range in length from 60-66Ám, and in width from 54-63Ám; 6 complete specimens measured.
Variability. Most of the variability is in the development of the parasutural features. On some specimens, only septa are present; on others septa and folds occur, and no specimen was found with folds only. The paraplates bordered by folds are usually, but not exclusively, those adjacent to the parasulcus and the paracingulum. On the fold bound paraplates, the dark marginal areas where the periphragm and endophragm are separated, stand in contrast to the lighter central areas where the two wall layers are in contact. This condition imposes a "window-pane" appearance on the paraplates and has been observed on other species of Impagidinium. It is characteristically developed on Carpodinium granulatum Cookson & Eisenack emend. Leffingwell & Morgan 1977. Some specimens of I. phlyctaena have a few, widely scattered, small granules in addition to the processes and large granules.
Affinities:
Stover and Helby, 1987, p. 271: Impagidinium phlyctaena is similar to Pterodinium premnon Duxbury 1980, which is described as having an intratabular projection on each paraplate. Impagidinium phlyctaena lacks intratabular features on the apical and cingular paraplates, and on some paraplates the features are large granules rather than processes. Because the ventral aspect of P. premnon was not illustrated, no further comparison is possible.