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Cribroperidinium asarotum
Cribroperidinium asarotum Stevens, 1987
Holotype: Stevens, 1987, fig.5A-C
Locus typicus: Exmouth Plateau, W Australia
Stratum typicum: Early Berriasian
Original description: Stevens, 1987, p. 188
Cysts proximate and subspherical to rounded ellipsoidal in shape with a prominent,
bluntly tipped, solid, apical horn, 6-12Ám in length. Autophragm 2-4Ám thick, finely punctate (the punctae are less than 1Ám in diameter) to spongy, with low parasutural and intratabular ridges. Ridges 2-4 Ám high and 1-2 Ám wide.
Intratabular areas ornamented in part by low cylindrical features (4-7 Ám in diameter) delineated by muri (1-4 Ám high). These cylindrical features occur individually or in groups in close contact giving the appearance of a coarse, regular reticulum. These apparently reticulate areas may be confined to central intratabular areas but in other cases the cylindrical features appearing irregularly distributed over most of the paraplate. Archeopyle precingular, type P (3" only), extending from the paracingulum to close to the apical horn, 22-34 Ám long and 20-30 Ám wide. Operculum free, generally not present. Paratabulation expressed by the paracingulum, archeopyle and parasutural ridges. Due to the intratabular ridges and the nature of the ornament the paratabular formula uncertain. Paracingulum generally indicated by parasutural ridges, 3-4 Ám wide, subdivided and offset by one to two paracingulum widths. Parasulcus indicated by a deep, elongate, linear depression extending posteriorly, from just above the paracingulum, a distance of at least one half cyst length. Parasulcus bordered by parasutural ridges, subdivided into at least 4, smooth sulcal paraplates. A large flagellar scar generally present.
Measurements. Cyst length (including apical horn) 73(87.5)102 Ám, cyst width 62(75)86 Ám (27 specimens).
Variability. Cyst size varies from moderate to large, and cyst shape, though generally subspherical to rounded ellipsoidal (Fig.5A,F), may be elongate ellipsoidal (Fig.51). The low cylindrical features vary in size (Fig.5C,I) and degree of interconnection (Fig.5C,G). The archeopyle is always large (Fig.5G,J), the
parasulcus is always delineated and a flagellar scar is generally present (Fig.5D,H). The apical horn varies in size and shape due to the presence of high muri (Fig.5F) and/or a thickening of the spongy autophragm (Fig.5D).
Affinities:
Stevens, 1987, p. 188: Cribroperidinium asarotum most closely resembles Apteodinium maculatum Eisenack & Cookson 1960 in having groups of raised, cylindrical intratabular features. However, in A. maculatum these features are described as " . . . thickened areas with circular outlines" and intratabular accessory ridges are absent. Cribroperidinium sepimentum Neale & Sarjeant 1962 and C. cooksoniae Norvick 1976 resemble C. asarotum in some respects, the former having a finely peautophragm and tgm and the latter having an irregular network of intratabular accessory ridges. Both species, however, lack any cylindrical intratabular features.
Holotype: Stevens, 1987, fig.5A-C
Locus typicus: Exmouth Plateau, W Australia
Stratum typicum: Early Berriasian
Original description: Stevens, 1987, p. 188
Cysts proximate and subspherical to rounded ellipsoidal in shape with a prominent,
bluntly tipped, solid, apical horn, 6-12Ám in length. Autophragm 2-4Ám thick, finely punctate (the punctae are less than 1Ám in diameter) to spongy, with low parasutural and intratabular ridges. Ridges 2-4 Ám high and 1-2 Ám wide.
Intratabular areas ornamented in part by low cylindrical features (4-7 Ám in diameter) delineated by muri (1-4 Ám high). These cylindrical features occur individually or in groups in close contact giving the appearance of a coarse, regular reticulum. These apparently reticulate areas may be confined to central intratabular areas but in other cases the cylindrical features appearing irregularly distributed over most of the paraplate. Archeopyle precingular, type P (3" only), extending from the paracingulum to close to the apical horn, 22-34 Ám long and 20-30 Ám wide. Operculum free, generally not present. Paratabulation expressed by the paracingulum, archeopyle and parasutural ridges. Due to the intratabular ridges and the nature of the ornament the paratabular formula uncertain. Paracingulum generally indicated by parasutural ridges, 3-4 Ám wide, subdivided and offset by one to two paracingulum widths. Parasulcus indicated by a deep, elongate, linear depression extending posteriorly, from just above the paracingulum, a distance of at least one half cyst length. Parasulcus bordered by parasutural ridges, subdivided into at least 4, smooth sulcal paraplates. A large flagellar scar generally present.
Measurements. Cyst length (including apical horn) 73(87.5)102 Ám, cyst width 62(75)86 Ám (27 specimens).
Variability. Cyst size varies from moderate to large, and cyst shape, though generally subspherical to rounded ellipsoidal (Fig.5A,F), may be elongate ellipsoidal (Fig.51). The low cylindrical features vary in size (Fig.5C,I) and degree of interconnection (Fig.5C,G). The archeopyle is always large (Fig.5G,J), the
parasulcus is always delineated and a flagellar scar is generally present (Fig.5D,H). The apical horn varies in size and shape due to the presence of high muri (Fig.5F) and/or a thickening of the spongy autophragm (Fig.5D).
Affinities:
Stevens, 1987, p. 188: Cribroperidinium asarotum most closely resembles Apteodinium maculatum Eisenack & Cookson 1960 in having groups of raised, cylindrical intratabular features. However, in A. maculatum these features are described as " . . . thickened areas with circular outlines" and intratabular accessory ridges are absent. Cribroperidinium sepimentum Neale & Sarjeant 1962 and C. cooksoniae Norvick 1976 resemble C. asarotum in some respects, the former having a finely peautophragm and tgm and the latter having an irregular network of intratabular accessory ridges. Both species, however, lack any cylindrical intratabular features.