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Ataxiodinium zevenboomii
From Fensome et al., 2019:
Ataxiodinium zevenboomii Head, 1997, p.171–172, fig.5; fig.6, nos.4–6,16; fig.18, nos.5–6. Holotype: Head, 1997, fig.6, nos.4–9. Taxonomic junior synonym: Ataxiodinium elongatum (name not validly published), according to Head (1997, p.171–172).
Age: middle Pliocene.
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Original description: [Head, 1997, p. 171-172]:
ATAXIODINIUM ZEVENBOOMII new species
Figures 5, 6.4-6.16, 18.5, 18.6
Ataxiodinium sp. nov. HEAD, EDWARDS, AND STEIDINGER, 1989a, vol. 2, p. 2, fig. 10. Ataxiodinium sp. McMINN, 1992b, p. 156, pl. 4, fig. 12, 13.
"Ataxiodinium elongatum" sp. nov. (ms. name). ZEVENBOOM AND SANTARELLI in Zevenboom, 1995, p. 141, 142, pl. 1, figs. 7-12.
Diagnosis. -- Cysts cavate with elongate to ovoid endoblast and slight or no dorsoventral compression. Endoblast consists of smooth, thin-walled, unstratified pedium. Periblast consists of thin-walled, unstratified tegillum with smooth or finely and faintly granulate and/or punctate surface. Tegillum attached to pedium around the archeopyle margins and by numerous funnel shaped invaginations distributed unevenly over the entire cyst. Archeopyle precingular Type P(3’’) with margins slightly irregular, angles well developed, no accessory sutures; operculum free. Tabulation elsewhere expressed obscurely.
Description. - Pedium and tegillum are each about 3 μm or less in thickness; pedium may be slightly thicker than tegillum. Distance separating tegillum from pedium is somewhat variable over the cyst. Funnel shaped invaginations of the tegillum have an irregular, possibly intratabular, distribution. Tegillum occasionally forms folds suggesting tabulation. Granules about 0.2 μm high and small perforations less than 0.2 μm in diameter occur on the surface of one specimen analyzed by SEM (Figure 18.5, 18.6).
Dimensions. - Holotype: endoblast length, 34 μm; endoblast width 23 μm; periblast length, 38 μm; periblast width 29 μm; maximum wall separation at ambitus, 4.5 μm. Range: endoblast length 26(32.3)43 μm, standard deviation 4.0; endoblast equatorial diameter, 18(22.6)26 μm, standard deviation, 2.2; periblast length, 31(37.4)50 μm, standard deviation, 4.5; periblast equatorial diameter, 24(27.9)32 μm, standard deviation, 2.2; maximum wall separation at ambitus, ca. 2.9(4.1)5.7 μm; ratio of endoblast length/equatorial diameter, 1.1(1.43)1.7, standard deviation, 0.16. Twenty-nine specimens were measured. See also Figure 5.
Comparison. - Ataxiodinium choane Reid, 1974, described from Recent sediments of England, differs in having a subspherical rather than elongate endoblast, in possessing less densely distributed funnel shaped invaginations of the tegillum, and in its greater separation of wall layers. Ataxiodinium confusum Versteegh and Zevenboom, 1995, described from the lower Pliocene of Italy, has a spherical to subspherical endoblast and more-or-less continuous cavation surrounnding the endoblast in dorso-ventral view.
Etymology. - Named in honor of D. Zevenboom for his contributions to Neogene dinoflagellate studies of the Mediterranean.
Holotype. - Figure 6.4-6.9. Sample CCS4, slide 1; England Finder reference J13/0. ROM 52492.
Type stratum and locality. - Sudbourne Member of the Coralline Crag Formation at Rockhall Wood, Suffolk.
Occurrence. - Mid Pliocene of Eastern England (Head et al., 1989a; this study); upper Miocene and lower Pliocene of The Netherlands (as “Ataxiodinium elongatum” in Zevenboom and Santarelli in Zevenboom, 1995); and Pliocene or lower Pleistocene of Australia (as Ataxiodinium sp. In McMinn, 1992b).
Ataxiodinium zevenboomii Head, 1997, p.171–172, fig.5; fig.6, nos.4–6,16; fig.18, nos.5–6. Holotype: Head, 1997, fig.6, nos.4–9. Taxonomic junior synonym: Ataxiodinium elongatum (name not validly published), according to Head (1997, p.171–172).
Age: middle Pliocene.
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Original description: [Head, 1997, p. 171-172]:
ATAXIODINIUM ZEVENBOOMII new species
Figures 5, 6.4-6.16, 18.5, 18.6
Ataxiodinium sp. nov. HEAD, EDWARDS, AND STEIDINGER, 1989a, vol. 2, p. 2, fig. 10. Ataxiodinium sp. McMINN, 1992b, p. 156, pl. 4, fig. 12, 13.
"Ataxiodinium elongatum" sp. nov. (ms. name). ZEVENBOOM AND SANTARELLI in Zevenboom, 1995, p. 141, 142, pl. 1, figs. 7-12.
Diagnosis. -- Cysts cavate with elongate to ovoid endoblast and slight or no dorsoventral compression. Endoblast consists of smooth, thin-walled, unstratified pedium. Periblast consists of thin-walled, unstratified tegillum with smooth or finely and faintly granulate and/or punctate surface. Tegillum attached to pedium around the archeopyle margins and by numerous funnel shaped invaginations distributed unevenly over the entire cyst. Archeopyle precingular Type P(3’’) with margins slightly irregular, angles well developed, no accessory sutures; operculum free. Tabulation elsewhere expressed obscurely.
Description. - Pedium and tegillum are each about 3 μm or less in thickness; pedium may be slightly thicker than tegillum. Distance separating tegillum from pedium is somewhat variable over the cyst. Funnel shaped invaginations of the tegillum have an irregular, possibly intratabular, distribution. Tegillum occasionally forms folds suggesting tabulation. Granules about 0.2 μm high and small perforations less than 0.2 μm in diameter occur on the surface of one specimen analyzed by SEM (Figure 18.5, 18.6).
Dimensions. - Holotype: endoblast length, 34 μm; endoblast width 23 μm; periblast length, 38 μm; periblast width 29 μm; maximum wall separation at ambitus, 4.5 μm. Range: endoblast length 26(32.3)43 μm, standard deviation 4.0; endoblast equatorial diameter, 18(22.6)26 μm, standard deviation, 2.2; periblast length, 31(37.4)50 μm, standard deviation, 4.5; periblast equatorial diameter, 24(27.9)32 μm, standard deviation, 2.2; maximum wall separation at ambitus, ca. 2.9(4.1)5.7 μm; ratio of endoblast length/equatorial diameter, 1.1(1.43)1.7, standard deviation, 0.16. Twenty-nine specimens were measured. See also Figure 5.
Comparison. - Ataxiodinium choane Reid, 1974, described from Recent sediments of England, differs in having a subspherical rather than elongate endoblast, in possessing less densely distributed funnel shaped invaginations of the tegillum, and in its greater separation of wall layers. Ataxiodinium confusum Versteegh and Zevenboom, 1995, described from the lower Pliocene of Italy, has a spherical to subspherical endoblast and more-or-less continuous cavation surrounnding the endoblast in dorso-ventral view.
Etymology. - Named in honor of D. Zevenboom for his contributions to Neogene dinoflagellate studies of the Mediterranean.
Holotype. - Figure 6.4-6.9. Sample CCS4, slide 1; England Finder reference J13/0. ROM 52492.
Type stratum and locality. - Sudbourne Member of the Coralline Crag Formation at Rockhall Wood, Suffolk.
Occurrence. - Mid Pliocene of Eastern England (Head et al., 1989a; this study); upper Miocene and lower Pliocene of The Netherlands (as “Ataxiodinium elongatum” in Zevenboom and Santarelli in Zevenboom, 1995); and Pliocene or lower Pleistocene of Australia (as Ataxiodinium sp. In McMinn, 1992b).