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Atlantodinium jurassicum
Atlantodinium jurassicum, Zotto et al., 1987
Holotype: Zotto et al., 1987, pl. 4, fig. 6a-b
Locus typicus: DSDP-site 100, SW North Atlantic
Stratum typicum: Kimmeridgian
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Original description: [Zotto et al., 1987, p. 202-203]:
Description:
Proximochorate-septate cysts with subpolygonal outline. Compression folds are rare or absent.
Cyst wall less than 0.5 µm thick. Cyst wall consists of one or two layers; pericoels absent.
Apical and antapical horns lacking.
Cingulum well-developed; it is offset adjacent the sulcus approximately one cingulum-width.
Sulcus is well-developed and more-or-less straight.
Tabulation is well-developed on the cyst, and is expressed by sharply polygonal penitabular septa which are low-lying and alveolate; alveolae concentrated near the base of the septa. Intratabular areas of plates characterized by thinly rimmed small perforations which penetrate the cyst wall. Cyst surface otherwise smooth. Tabulation formula: gonyaulacacean, Xpr, X", Xa, 6"", 6c, 6""", 1p, 1"""". Sulcal tabulation ps, ls. rs, as. Tabulation of the apical series and related plates not known, since no specimens with the operculum intact have been observed. The precingular series consists of rectangular or trapezoidal plates, with the exception of precingular plate 3"" which may be pentagonal. Precingular plate 6"" is rectangular, with the lateral margins subparallel to the sulcus. The plates of the cingulum are transversely elongated rectangular. The postcingular series consists of a small but discrete first postcingular plate (1""") and then progressively larger second (2""") and third (3""") postcingular plates. Plate 3""" does not contact the sulcus. The fourth postcingular plate (4""") is relatively large and is offset to the right of precingular plate 3""". The sixth (6""") postcingular plate is smaller, trapezoidal, and is attenuated towards the antapical end of the cyst. The single posterior intercalary plate (1p) is relatively large and pentagonal. The single antapical plate (1"""") is six sided; it is larger and is offset on the ventral surface. The sulcus consists of four discrete plates. The posterior sulcal plate (ps) is pentagonal and may (or may not) possess a medial split at its anteriormost margin. The left sulcal (ls) and right sulcal (rs) plates are rectangular or nearly so. The anterior sulcal plate (as) is trapezoidal with lateral margins which are attenuated towards the apical end of the cyst.
Archeopyle apical, with accessory sutures developed in the dorsal precingular series. Operculum free, and the number of opercular pieces is not known.
Dimensions:
Size of cysts ranges 38 to 55 µm high, 40 to 60 µm wide. Ten specimens were measured.
Affinities:
Atlantodinium jurassicum is distinguished from Alisocysta circumtabulatum by its sexiform hypocystal configuration, by the nature of its cyst wall and by the sharply polygonal outline of its penitabular septa. It is distinguished from Amphorula metaelliptica by the possession of transversely rectangular septa of the cingulum. Another similar species, Histiophora ornata, does not exhibit tabulation of the cingulum.
Holotype: Zotto et al., 1987, pl. 4, fig. 6a-b
Locus typicus: DSDP-site 100, SW North Atlantic
Stratum typicum: Kimmeridgian
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Zotto et al., 1987, p. 202-203]:
Description:
Proximochorate-septate cysts with subpolygonal outline. Compression folds are rare or absent.
Cyst wall less than 0.5 µm thick. Cyst wall consists of one or two layers; pericoels absent.
Apical and antapical horns lacking.
Cingulum well-developed; it is offset adjacent the sulcus approximately one cingulum-width.
Sulcus is well-developed and more-or-less straight.
Tabulation is well-developed on the cyst, and is expressed by sharply polygonal penitabular septa which are low-lying and alveolate; alveolae concentrated near the base of the septa. Intratabular areas of plates characterized by thinly rimmed small perforations which penetrate the cyst wall. Cyst surface otherwise smooth. Tabulation formula: gonyaulacacean, Xpr, X", Xa, 6"", 6c, 6""", 1p, 1"""". Sulcal tabulation ps, ls. rs, as. Tabulation of the apical series and related plates not known, since no specimens with the operculum intact have been observed. The precingular series consists of rectangular or trapezoidal plates, with the exception of precingular plate 3"" which may be pentagonal. Precingular plate 6"" is rectangular, with the lateral margins subparallel to the sulcus. The plates of the cingulum are transversely elongated rectangular. The postcingular series consists of a small but discrete first postcingular plate (1""") and then progressively larger second (2""") and third (3""") postcingular plates. Plate 3""" does not contact the sulcus. The fourth postcingular plate (4""") is relatively large and is offset to the right of precingular plate 3""". The sixth (6""") postcingular plate is smaller, trapezoidal, and is attenuated towards the antapical end of the cyst. The single posterior intercalary plate (1p) is relatively large and pentagonal. The single antapical plate (1"""") is six sided; it is larger and is offset on the ventral surface. The sulcus consists of four discrete plates. The posterior sulcal plate (ps) is pentagonal and may (or may not) possess a medial split at its anteriormost margin. The left sulcal (ls) and right sulcal (rs) plates are rectangular or nearly so. The anterior sulcal plate (as) is trapezoidal with lateral margins which are attenuated towards the apical end of the cyst.
Archeopyle apical, with accessory sutures developed in the dorsal precingular series. Operculum free, and the number of opercular pieces is not known.
Dimensions:
Size of cysts ranges 38 to 55 µm high, 40 to 60 µm wide. Ten specimens were measured.
Affinities:
Atlantodinium jurassicum is distinguished from Alisocysta circumtabulatum by its sexiform hypocystal configuration, by the nature of its cyst wall and by the sharply polygonal outline of its penitabular septa. It is distinguished from Amphorula metaelliptica by the possession of transversely rectangular septa of the cingulum. Another similar species, Histiophora ornata, does not exhibit tabulation of the cingulum.