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Ambonosphaera calloviana
Ambonosphaera calloviana, Fensome, 1979
Originally (and now) Ambonosphaera, subsequently Polygonifera. Brenner, 1988, transferred this species to Polygonifera Habib, 1972; however, Prauss, 1989, retained it in Ambonosphaera.
Holotype: Fensome, 1979, pl.7, fig.3,6,9, text-fig.16B-C
Paratypes: Fensome, 1979
Locus typicus: Vardeklöft Formation, W. of Olympen, Jameson Land, E. Greenland
Stratum typicum: Early Callovian
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Original description: [Fensome, 1979, p. 51-54]:
Diagnosis:
A species of dinoflagellate having a small cavate cyst; the pericyst is subpolygonal and the endocyst is usually ovoidal to spheroidal. Polygonality is imparted to the pericyst by crest-like bulges bearing parasutural ridges;
the paratabulation is 4', 5 or 6'', 7c, 6 or 7''',1p, 1pv, ?2'''', 3 or 3 + s.
The endophragm is thick and coarsely and irregularly granular; the periphragm is thin, translucent and less coarsely granular than the endophragm.
Usually small apical and antapical percoels are present; separation of the two wall layers other than at the apex and antapex is variable both within a single specimen and from one specimen to another. Rarely the two wall layers may be closely appressed over almost all of the cyst surface.
The archeopyle is apical; the operculum may be attached or detached.
Description (annotated):
There are four small apical paraplates, of which 1' extends towards the parasulcus. When the archeopyle is developed, the position of the paraplate 1' is clearly indicated by an indentation of the archeopyle margin projecting into the parasulcus. Paraplate 1'' to 4'' are of approximately equal size.
The parasuture dividing 5'' and 6'' is at most only faintly marked and is sometimes absent; indeed, it is not possible to be confident about the presence of two plates here.
The paracingulum is laevorotatory, its two ends separated by a distance equal to, or slightly greater than, one paracingulum width. Paraplate 1c is small, paraplate 7c seems to vary in size.
The parasulcus is straight to slightly sinuous, narrow and depressed.
On the hypocyst to the left of the parasulcus the paratabulation is again indistinct. The postcingular series in this area is reduced in size because of the presence of a moderately large posterior intercalary paraplate. However, whether one or two postcingular paraplates are present is not clear. Paraplate ?6''' is usually well marked; it is narrow and elongate, broadening towards the antapex. The number of antapical paraplates is not clear. At least one is present and ventrally inclined but low, poorly marked ridges in the region of the antapex may indicate the presence of more paraplates there.
Dimensions:
Holotype (archeopyle not formed): Length endocyst, 38 µm, pericyst, 45 µm. Breadth endocyst, 38 µm, pericyst, 42 µm.
Range (eight specimens): Archeopyle formed: length endocyst, 37-40 µm, pericyst, 42-45 µm. Archeopyle not formed: length endocyst, 34-46 µm, pericyst, 40-49 µm.
Breadth: endocyst 26-38 µm, pericyst 32-42 µm.
Affinities:
Ambonosphaera jurassica (Gitmez and Sarjeant, 1972) Fensome, 1979 is distinguished from A. calloviana by its more rounded outline, the more consistent width of its pericoels in ambital view and by its less well developed paratabulation. Dingodinium minutum Dodekova, 1975, recorded from the Upper Bathonian of Bulgaria, appears to be similar to A. calloviana, at least superficially. The two species appear to be comparable in size, in the nature of their parasutural crests, and in the development of their archeopyles. D. minutum, however, differs from A. calloviana in the detail of its paratabulation. A. calloviana does not possess any anterior intercalary paraplates and certainly has at least six postcingular paraplates, including a small elongate paraplate immediately to the right of the parasulcus. Dodekova reports two possible anterior intercalary paraplates and five postcingular paraplates from D. minutum. If Dodekova's plate 5, fig. 13 is indeed on the ventral surface, D. minutum can be further differentiated from A. calloviana by its asymmetrically situated endocyst, its circular paracingulum and its relatively indistinct parasulcus. Because of its determinable paratabulation and apparently apical archeopyle, D. minutum possibly merits generic re-attribution, a conclusion also reached by Sarjeant, (1978). Its paratabulation, as described by Dodekova, however, does not accord with that of Ambonosphaera.
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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.
Ambonosphaera calloviana Fensome, 1979, emend. Prauss, 1989 is a cavate cyst with coarsely and irregularly granular endocyst. Usually small apical and antapical pericoels are present. Rarely the two wall layers may be closely appressed over almost all of the cyst surface Prauss (1989) emended the genus to allow for the development of secondary sutures between the precingulars and to include proximate/cavate to proximate/chorocavate cysts. He gave the tabulation formula as XPR, 4', 5-6", 6-7c, 5-6"’, 0-1p, 1"”, ns.
Size: endocyst 37-40 µm, pericyst 42-45 µm.
Originally (and now) Ambonosphaera, subsequently Polygonifera. Brenner, 1988, transferred this species to Polygonifera Habib, 1972; however, Prauss, 1989, retained it in Ambonosphaera.
Holotype: Fensome, 1979, pl.7, fig.3,6,9, text-fig.16B-C
Paratypes: Fensome, 1979
Locus typicus: Vardeklöft Formation, W. of Olympen, Jameson Land, E. Greenland
Stratum typicum: Early Callovian
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Fensome, 1979, p. 51-54]:
Diagnosis:
A species of dinoflagellate having a small cavate cyst; the pericyst is subpolygonal and the endocyst is usually ovoidal to spheroidal. Polygonality is imparted to the pericyst by crest-like bulges bearing parasutural ridges;
the paratabulation is 4', 5 or 6'', 7c, 6 or 7''',1p, 1pv, ?2'''', 3 or 3 + s.
The endophragm is thick and coarsely and irregularly granular; the periphragm is thin, translucent and less coarsely granular than the endophragm.
Usually small apical and antapical percoels are present; separation of the two wall layers other than at the apex and antapex is variable both within a single specimen and from one specimen to another. Rarely the two wall layers may be closely appressed over almost all of the cyst surface.
The archeopyle is apical; the operculum may be attached or detached.
Description (annotated):
There are four small apical paraplates, of which 1' extends towards the parasulcus. When the archeopyle is developed, the position of the paraplate 1' is clearly indicated by an indentation of the archeopyle margin projecting into the parasulcus. Paraplate 1'' to 4'' are of approximately equal size.
The parasuture dividing 5'' and 6'' is at most only faintly marked and is sometimes absent; indeed, it is not possible to be confident about the presence of two plates here.
The paracingulum is laevorotatory, its two ends separated by a distance equal to, or slightly greater than, one paracingulum width. Paraplate 1c is small, paraplate 7c seems to vary in size.
The parasulcus is straight to slightly sinuous, narrow and depressed.
On the hypocyst to the left of the parasulcus the paratabulation is again indistinct. The postcingular series in this area is reduced in size because of the presence of a moderately large posterior intercalary paraplate. However, whether one or two postcingular paraplates are present is not clear. Paraplate ?6''' is usually well marked; it is narrow and elongate, broadening towards the antapex. The number of antapical paraplates is not clear. At least one is present and ventrally inclined but low, poorly marked ridges in the region of the antapex may indicate the presence of more paraplates there.
Dimensions:
Holotype (archeopyle not formed): Length endocyst, 38 µm, pericyst, 45 µm. Breadth endocyst, 38 µm, pericyst, 42 µm.
Range (eight specimens): Archeopyle formed: length endocyst, 37-40 µm, pericyst, 42-45 µm. Archeopyle not formed: length endocyst, 34-46 µm, pericyst, 40-49 µm.
Breadth: endocyst 26-38 µm, pericyst 32-42 µm.
Affinities:
Ambonosphaera jurassica (Gitmez and Sarjeant, 1972) Fensome, 1979 is distinguished from A. calloviana by its more rounded outline, the more consistent width of its pericoels in ambital view and by its less well developed paratabulation. Dingodinium minutum Dodekova, 1975, recorded from the Upper Bathonian of Bulgaria, appears to be similar to A. calloviana, at least superficially. The two species appear to be comparable in size, in the nature of their parasutural crests, and in the development of their archeopyles. D. minutum, however, differs from A. calloviana in the detail of its paratabulation. A. calloviana does not possess any anterior intercalary paraplates and certainly has at least six postcingular paraplates, including a small elongate paraplate immediately to the right of the parasulcus. Dodekova reports two possible anterior intercalary paraplates and five postcingular paraplates from D. minutum. If Dodekova's plate 5, fig. 13 is indeed on the ventral surface, D. minutum can be further differentiated from A. calloviana by its asymmetrically situated endocyst, its circular paracingulum and its relatively indistinct parasulcus. Because of its determinable paratabulation and apparently apical archeopyle, D. minutum possibly merits generic re-attribution, a conclusion also reached by Sarjeant, (1978). Its paratabulation, as described by Dodekova, however, does not accord with that of Ambonosphaera.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Notes:
G.L. Williams short notes on species, Mesozoic-Cenozoic dinocyst course, Urbino, Italy, May 17-22, 1999 - LPP VIEWER CD-ROM 99.5.
Ambonosphaera calloviana Fensome, 1979, emend. Prauss, 1989 is a cavate cyst with coarsely and irregularly granular endocyst. Usually small apical and antapical pericoels are present. Rarely the two wall layers may be closely appressed over almost all of the cyst surface Prauss (1989) emended the genus to allow for the development of secondary sutures between the precingulars and to include proximate/cavate to proximate/chorocavate cysts. He gave the tabulation formula as XPR, 4', 5-6", 6-7c, 5-6"’, 0-1p, 1"”, ns.
Size: endocyst 37-40 µm, pericyst 42-45 µm.