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Isabelidinium viborgense
Isabelidinium? viborgense Heilmann-Clausen, 1985
Heilmann-Clausen, 1985, questionably included this species in Isabelidinizlm.
Holotype: Heilmann-Clausen, 1985, pl.1, figs.24-25, text-fig.9A
Locus typicus: Viborg 1, Jylland, Denmark
Stratum typicum: Selandian, Late Paleocene
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G.L. Williams short notes on species, Mesozoic-Cenozoic dinocyst course, Urbino, Italy, May 17-22, 1999 - LPP VIEWER CD-ROM 99.5.
Isabelidinium viborgense Heilmann-Clausen, 1985. Heilmann-Clausen (1985) noted that this species is smooth-walled, circumcavate, the pericyst is almost pentagonal, the apical and antapical horns being strongly reduced. Epi and hypopericyst are of almost equal size. The broad and deeply depressed paracingulum gives rise to deep notches of the lateral margins of the cyst. The deep parasulcus extends to the antapical corners. The peri-archeopyle is intercalary or is an intercalary-precingular combination type. Two additional openings are present in the periphragm: one near the apex on the ventral surface, and another on the posterior part of the parasulcus. The endocyst is subcircular in dorso-ventral view and thinner-walled than the pericystThis species is questionably included in Isabelidinium because of the well developed cingulum. . Size: pericyst length 47-70 µm, width 37-57 µm, endocyst length 27-41 µm, width 26-41 µm.
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Original diagnosis: Heilmann-Clausen, 1985, p. 22-23
A smooth-walled, circumcavate, peridiniacean cyst. The pericyst-ambitus is almost pentagonal, the apieal and both antapical horns being strongly redueed. Epi- and hypo-perieyst are of almost equal size. The broad and deeply depressed paraeingulum gives rise to deep notehes of the lateral margins of the eyst. The deep parasuleus extends to the antapical corners. The peri-archaeopyle is intercalary, or is an intercalaryprecingular combination type. Two additional openings are present in the periphragm: one near the apex on the ventral surface, and an other opening is present in the posterior part of the parasulcus. The endocyst is subeireular in ambitus and thinner-walled than the pericyst.
Original description: Heilmann-Clausen, 1985, p.23
A circumcavate peridiniacean cyst.
Pericyst: The pericyst is smooth-walled and sub-pentagonal in ambitus. The lateral margin between apex and paracingulum is convex, while the posterior margin between the strongly reduced antapical horns is concave. The apex is truncate or concave. A broad and deeply depressed, scarcely offset paracingulum is present in an equatorial position, and the epicyst and hypocyst are therefore almost equal in size. The parasulcus is broad and deep; it is mainly confined to the hypocyst, and extends to the two antapical corners. The peri-archaeopyle is either intercalary with an operculum attached at the posterior margin, type la(2a) (fig. 9B, C), or is a combination-archaeopyle, type IPa(2a, 4") (fig. 9A, D). In addition to the archaeopyle two other openings are present in the periphragm (fig. 9). One opening is situated near the apex, on the ventral surface. The other is located in the posterior part of the parasulcus; it is offset to the right and often appears to be composed of two coalescent, round holes. Endocyst: The endocyst is thin-walled and smooth with a subcircular ambitus. It is clearly separated from the periphragm in the ambital plane. An endo-archaeopyle is only rarely visible (fig. 9D). It appears to be a hexa 1(2a) archaeopyle. A few specimens without a detaetable central body have been seen. Dimensions Pericyst, Iength. max., (mean), min.: 71 (59) 47 Ám, width: 57 (49) 37 Ám. Endocyst, length: 41 (34) 27 Ám, width: 41 (34) 26 Ám.
(11 specimens measured). Holotype: pericyst length 58 Ám. width 41 Ám; endocyst length 34 Ám, width 33 Ám.
Affinities:
Heilmann-Clausen, 1985, p. 23: In typical specimens of Isabelidinium the paracingulum is not distinct. The present species has a strongly developed paracingulum and is therefore only provisionally referred to Isabelidinium.
I. ? viborgense resembles, to some extent, Senegalnium ? dilwynense (Cookson & Eisenack) Stover & Evitt 1978. The latter species differs, however, in several respects: I ) the epicyst is much longer than the hypocyst, 2) a left antapical horn is well developed, 3) the endocyst is much larger, 4) the periphragm has a distinct pattern of longitudinal folds and 5) no additional openings seem to be present in the periphragm.
The possible functions of the additional openings in the periphragm are not known. The small apical concavity probably corresponds to the position of the apical pore-platelet of the theca. The opening, which is placed ventrally and posterior to this concavity, may reflect the position of the ventral apical platelet of the theca.
Holes with a well-defined antapical or posterior-ventral position are present in widespread cavate genera, such as the peridiniacean genera Ovoidinium and Angustidinium and the gonyaulacaeean genera Sirmiodinium, Tubotuborella and Hystrichosphaeropsis. Sarjeant (1974) proposed that a posterior-ventrally placed hole be termed an opisthopyle, and that the function was to release internal pressures during excystment.
Heilmann-Clausen, 1985, questionably included this species in Isabelidinizlm.
Holotype: Heilmann-Clausen, 1985, pl.1, figs.24-25, text-fig.9A
Locus typicus: Viborg 1, Jylland, Denmark
Stratum typicum: Selandian, Late Paleocene
--------------------------------------------------
G.L. Williams short notes on species, Mesozoic-Cenozoic dinocyst course, Urbino, Italy, May 17-22, 1999 - LPP VIEWER CD-ROM 99.5.
Isabelidinium viborgense Heilmann-Clausen, 1985. Heilmann-Clausen (1985) noted that this species is smooth-walled, circumcavate, the pericyst is almost pentagonal, the apical and antapical horns being strongly reduced. Epi and hypopericyst are of almost equal size. The broad and deeply depressed paracingulum gives rise to deep notches of the lateral margins of the cyst. The deep parasulcus extends to the antapical corners. The peri-archeopyle is intercalary or is an intercalary-precingular combination type. Two additional openings are present in the periphragm: one near the apex on the ventral surface, and another on the posterior part of the parasulcus. The endocyst is subcircular in dorso-ventral view and thinner-walled than the pericystThis species is questionably included in Isabelidinium because of the well developed cingulum. . Size: pericyst length 47-70 µm, width 37-57 µm, endocyst length 27-41 µm, width 26-41 µm.
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Original diagnosis: Heilmann-Clausen, 1985, p. 22-23
A smooth-walled, circumcavate, peridiniacean cyst. The pericyst-ambitus is almost pentagonal, the apieal and both antapical horns being strongly redueed. Epi- and hypo-perieyst are of almost equal size. The broad and deeply depressed paraeingulum gives rise to deep notehes of the lateral margins of the eyst. The deep parasuleus extends to the antapical corners. The peri-archaeopyle is intercalary, or is an intercalaryprecingular combination type. Two additional openings are present in the periphragm: one near the apex on the ventral surface, and an other opening is present in the posterior part of the parasulcus. The endocyst is subeireular in ambitus and thinner-walled than the pericyst.
Original description: Heilmann-Clausen, 1985, p.23
A circumcavate peridiniacean cyst.
Pericyst: The pericyst is smooth-walled and sub-pentagonal in ambitus. The lateral margin between apex and paracingulum is convex, while the posterior margin between the strongly reduced antapical horns is concave. The apex is truncate or concave. A broad and deeply depressed, scarcely offset paracingulum is present in an equatorial position, and the epicyst and hypocyst are therefore almost equal in size. The parasulcus is broad and deep; it is mainly confined to the hypocyst, and extends to the two antapical corners. The peri-archaeopyle is either intercalary with an operculum attached at the posterior margin, type la(2a) (fig. 9B, C), or is a combination-archaeopyle, type IPa(2a, 4") (fig. 9A, D). In addition to the archaeopyle two other openings are present in the periphragm (fig. 9). One opening is situated near the apex, on the ventral surface. The other is located in the posterior part of the parasulcus; it is offset to the right and often appears to be composed of two coalescent, round holes. Endocyst: The endocyst is thin-walled and smooth with a subcircular ambitus. It is clearly separated from the periphragm in the ambital plane. An endo-archaeopyle is only rarely visible (fig. 9D). It appears to be a hexa 1(2a) archaeopyle. A few specimens without a detaetable central body have been seen. Dimensions Pericyst, Iength. max., (mean), min.: 71 (59) 47 Ám, width: 57 (49) 37 Ám. Endocyst, length: 41 (34) 27 Ám, width: 41 (34) 26 Ám.
(11 specimens measured). Holotype: pericyst length 58 Ám. width 41 Ám; endocyst length 34 Ám, width 33 Ám.
Affinities:
Heilmann-Clausen, 1985, p. 23: In typical specimens of Isabelidinium the paracingulum is not distinct. The present species has a strongly developed paracingulum and is therefore only provisionally referred to Isabelidinium.
I. ? viborgense resembles, to some extent, Senegalnium ? dilwynense (Cookson & Eisenack) Stover & Evitt 1978. The latter species differs, however, in several respects: I ) the epicyst is much longer than the hypocyst, 2) a left antapical horn is well developed, 3) the endocyst is much larger, 4) the periphragm has a distinct pattern of longitudinal folds and 5) no additional openings seem to be present in the periphragm.
The possible functions of the additional openings in the periphragm are not known. The small apical concavity probably corresponds to the position of the apical pore-platelet of the theca. The opening, which is placed ventrally and posterior to this concavity, may reflect the position of the ventral apical platelet of the theca.
Holes with a well-defined antapical or posterior-ventral position are present in widespread cavate genera, such as the peridiniacean genera Ovoidinium and Angustidinium and the gonyaulacaeean genera Sirmiodinium, Tubotuborella and Hystrichosphaeropsis. Sarjeant (1974) proposed that a posterior-ventrally placed hole be termed an opisthopyle, and that the function was to release internal pressures during excystment.