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Alterbidinium circulum
From Fensome et al., 2019:
Alterbidinium circulum, (Heilmann-Clausen, 1985, p.16–17, pl.1, figs.1–8; text-fig.5) Lentin and Williams, 1989, p.13.
Holotype: Heilmann-Clausen, 1985, pl.1, figs.1–2.
Originally Alterbia (generic name illegitimate), subsequently (and now) Alterbidinium.
Age: Early Paleocene.
Locus typicus: Viborg 1, Jylland, Denmark
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Original description as Alterbia circula: [Heilmann-Clausen, 1985, p. 16-17]:
Diagnosis:
A species of Alterbia Lentin & Williams 1976, with the following specific characters: The cyst is circumcavate. The smooth pericyst has convex lateral margins of the epicyst. The right antapical horn is reduced, but not completely absent.
The peri-archaeopyle is intercalary, or an intercalary-precingular combination type. The shape of paraplate 2a is steno to isodeltaform to thetaform.
The endocyst is almost circular in ambitus and shows a faint paratabulation mid-dorsally. The endo-archaeopyle is intercalary. The endophragm is thicker than the periphragm.
Description:
A circumcavate peridiniacean cyst.
Pericyst: The pericyst is smooth-walled, and the outline is peridinioid.
The epicyst has convex lateral margins, "Shoulders", and an apical horn of moderate length with a truncated apex.
The left antapical horn is longer than the right one which may also be absent.
The paracingulum is clearly marked laterally by indentations of the periphragm, but otherwise is not expressed, or is only indicated by faint parasutural lines.
The parasulcus is only indicated as an indentation of the ventral surface of the hypocyst.
The peri-archaeopyle is intercalary, or is an intercalary-precingular combination type. The variation of the archaeopyle includes the types la(2a) (fig. SC, D), I(2a) (fig. SA) and (IPa)(2a, 4") (fig. SB). The shape of plate 2a is steno to iso - deltaform to thetaform.
Endocyst: The endocyst is thick-walled (about 1 µm) and finely granular, occasionally bearing a few large verrucae. The outline in dorsoventral view is almost perfectly circular to sub-pentagonal.
A paratabulation is expressed mid-dorsally as a hexa 1(2a) archaeopyle, and additionally as fine parasutural lines showing the paraplates 4", 3c and 3''', or parts of these paraplates (fig. 5).
Dimensions:
Pericyst, length, max., (mean), min.: 83 (73) 66 µm, width: 53 (46) 41 µm.
Endocyst, length: 46 (42) 37 µm, width: 45 (40) 35 µm. (10 specimens measured).
Holotype: pericyst length 75 µm, width 46 µm; endocyst length 43 µm, width 40 µm.
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Notes:
G.L. Williams short notes on species, Mesozoic-Cenozoic dinocyst course, Urbino, Italy, May 17-22, 1999 - LPP VIEWER CD-ROM 99.5.
Alterbidinium circulum (Heilmann-Clausen, 1986) Lentin and Williams, 1989, is circumcavate cyst and has a 2a or 2a + 4" archeopyle with the operculum remaining attached. 2a is steno- to isodeltaform to thetaform. The endocyst is almost circular and is faintly paratabulate mid-dorsally. The epicyst has shoulders and an apical horn of moderate length which is truncated. Cingulum not well marked except laterally.
Size: pericyst length 66-83 µm, breadth 41-53 µm. Endocyst length 37-46 µm, breadth 35-45 µm.
Alterbidinium circulum, (Heilmann-Clausen, 1985, p.16–17, pl.1, figs.1–8; text-fig.5) Lentin and Williams, 1989, p.13.
Holotype: Heilmann-Clausen, 1985, pl.1, figs.1–2.
Originally Alterbia (generic name illegitimate), subsequently (and now) Alterbidinium.
Age: Early Paleocene.
Locus typicus: Viborg 1, Jylland, Denmark
---------------------------------------------------------------------------------------------------
Original description as Alterbia circula: [Heilmann-Clausen, 1985, p. 16-17]:
Diagnosis:
A species of Alterbia Lentin & Williams 1976, with the following specific characters: The cyst is circumcavate. The smooth pericyst has convex lateral margins of the epicyst. The right antapical horn is reduced, but not completely absent.
The peri-archaeopyle is intercalary, or an intercalary-precingular combination type. The shape of paraplate 2a is steno to isodeltaform to thetaform.
The endocyst is almost circular in ambitus and shows a faint paratabulation mid-dorsally. The endo-archaeopyle is intercalary. The endophragm is thicker than the periphragm.
Description:
A circumcavate peridiniacean cyst.
Pericyst: The pericyst is smooth-walled, and the outline is peridinioid.
The epicyst has convex lateral margins, "Shoulders", and an apical horn of moderate length with a truncated apex.
The left antapical horn is longer than the right one which may also be absent.
The paracingulum is clearly marked laterally by indentations of the periphragm, but otherwise is not expressed, or is only indicated by faint parasutural lines.
The parasulcus is only indicated as an indentation of the ventral surface of the hypocyst.
The peri-archaeopyle is intercalary, or is an intercalary-precingular combination type. The variation of the archaeopyle includes the types la(2a) (fig. SC, D), I(2a) (fig. SA) and (IPa)(2a, 4") (fig. SB). The shape of plate 2a is steno to iso - deltaform to thetaform.
Endocyst: The endocyst is thick-walled (about 1 µm) and finely granular, occasionally bearing a few large verrucae. The outline in dorsoventral view is almost perfectly circular to sub-pentagonal.
A paratabulation is expressed mid-dorsally as a hexa 1(2a) archaeopyle, and additionally as fine parasutural lines showing the paraplates 4", 3c and 3''', or parts of these paraplates (fig. 5).
Dimensions:
Pericyst, length, max., (mean), min.: 83 (73) 66 µm, width: 53 (46) 41 µm.
Endocyst, length: 46 (42) 37 µm, width: 45 (40) 35 µm. (10 specimens measured).
Holotype: pericyst length 75 µm, width 46 µm; endocyst length 43 µm, width 40 µm.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Notes:
G.L. Williams short notes on species, Mesozoic-Cenozoic dinocyst course, Urbino, Italy, May 17-22, 1999 - LPP VIEWER CD-ROM 99.5.
Alterbidinium circulum (Heilmann-Clausen, 1986) Lentin and Williams, 1989, is circumcavate cyst and has a 2a or 2a + 4" archeopyle with the operculum remaining attached. 2a is steno- to isodeltaform to thetaform. The endocyst is almost circular and is faintly paratabulate mid-dorsally. The epicyst has shoulders and an apical horn of moderate length which is truncated. Cingulum not well marked except laterally.
Size: pericyst length 66-83 µm, breadth 41-53 µm. Endocyst length 37-46 µm, breadth 35-45 µm.