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Skuadinium assymmetricum
Skuadinium asymmetricum Riding and Helby, 2001a, p.15,17, figs.9A–I. Holotype: Riding and Helby, 2001a, figs.9H–I. Age: early Toarcian.
Description. Representatives of Skuadinium which have a reticulate to occasionally scabrate autophragm. The horns are highly variable; they range from relatively short to markedly elongate and may be pointed or rounded distally. In lateral view, the dorsal ridges of the epicyst and hypocyst are convex. The ventral side of the epicyst is, however, generally highly concave, while the ventral side of the hypocyst is normally straight to convex, although concave close to the antapical horn. The main reason for the asymmetrical nature of this form in lateral view is that the ventral side of the cyst is inflated. The ventral precingular, and particularly the postcingular paraplates, are markedly inflated close to the paracingulum, resulting in the parasulcus being deeply indented. Most specimens have a relatively large, subcircular brown accumulation body within the cyst. The paracingulum may sometimes be faintly indicated by autophragmal folds. An epicystal archaeopyle is suggested by relatively consistent tearing along the anterior margin of the paracingulum.
Domensions (µm, n=25): Min. (Mean) Max.
Length: 56 (72) 95
Width: 36 (50) 62
Width of fenestrae: 1 (2) 5
The measured specimens are from sidewall core samples in Skua-6 (2385.00m) and Skua-7A (2440.00m) wells.
Comments. The asymmetry of the epicyst in lateral view, caused by extension of the ventral side is diagnostic of this species. The shape of the epicyst, and often the hypocyst, in lateral view may impart a lateral outline superficially similar a lateral view of Nannoceratopsis (see Piel & Evitt, 1980). However, the profound differences in paratabulation distinguish Skuadinium asymmetricum from species of Nannosceratopsis. A definite archaeopyle has not been observed, but incomplete splits immediately anterior of the paracingulum strongly suggest that the archaeopyle type is epicystal.
Comparison. Skuadinium asymmetricum differs from the other species of the genus in its distinctively asymmetrical outline in lateral view and its reticulate autophragm. It is most similar to S. reticulatum, but lacks its symmetrical biconical shape, and has more variable ornament and commonly rounded horn extremities.
Derivation of name. From the marked asymmetry of the cyst in lateral view.
Holotype and type locality. Figs. 9H-I, CPC 35166, Skua-6 well, sidewall core sample at 2385.00m
Stratigraphical distribution. See Appendix 1 and Fig. 12
Description. Representatives of Skuadinium which have a reticulate to occasionally scabrate autophragm. The horns are highly variable; they range from relatively short to markedly elongate and may be pointed or rounded distally. In lateral view, the dorsal ridges of the epicyst and hypocyst are convex. The ventral side of the epicyst is, however, generally highly concave, while the ventral side of the hypocyst is normally straight to convex, although concave close to the antapical horn. The main reason for the asymmetrical nature of this form in lateral view is that the ventral side of the cyst is inflated. The ventral precingular, and particularly the postcingular paraplates, are markedly inflated close to the paracingulum, resulting in the parasulcus being deeply indented. Most specimens have a relatively large, subcircular brown accumulation body within the cyst. The paracingulum may sometimes be faintly indicated by autophragmal folds. An epicystal archaeopyle is suggested by relatively consistent tearing along the anterior margin of the paracingulum.
Domensions (µm, n=25): Min. (Mean) Max.
Length: 56 (72) 95
Width: 36 (50) 62
Width of fenestrae: 1 (2) 5
The measured specimens are from sidewall core samples in Skua-6 (2385.00m) and Skua-7A (2440.00m) wells.
Comments. The asymmetry of the epicyst in lateral view, caused by extension of the ventral side is diagnostic of this species. The shape of the epicyst, and often the hypocyst, in lateral view may impart a lateral outline superficially similar a lateral view of Nannoceratopsis (see Piel & Evitt, 1980). However, the profound differences in paratabulation distinguish Skuadinium asymmetricum from species of Nannosceratopsis. A definite archaeopyle has not been observed, but incomplete splits immediately anterior of the paracingulum strongly suggest that the archaeopyle type is epicystal.
Comparison. Skuadinium asymmetricum differs from the other species of the genus in its distinctively asymmetrical outline in lateral view and its reticulate autophragm. It is most similar to S. reticulatum, but lacks its symmetrical biconical shape, and has more variable ornament and commonly rounded horn extremities.
Derivation of name. From the marked asymmetry of the cyst in lateral view.
Holotype and type locality. Figs. 9H-I, CPC 35166, Skua-6 well, sidewall core sample at 2385.00m
Stratigraphical distribution. See Appendix 1 and Fig. 12