Back
Isabelidinium majae
Isabelidinium majae Schioler, 1993
Holotype: Schioler, 1993, pl.1, fig.1, text-fig.4a
Paratype: Schioler, 1993
Locus typicus: Well M-lOx, depth 1973.0m, Dan Field, Danish North Sea
Stratum typicum: Latest Maastrichtian
Original diagnosis: Schioler, 1993, p.108
A cavate peridinioid cyst with a smooth endo- and periphragm without indications of paracingulum. The ambitus shows overall axial symmetry. The periarcheopyle is lati-deltaform.
Original description: Schioler, 1993, p.108
Cavate peridinioid cyst. Cyst outline is almost bilateral symmetric in ambital view. The periphragm is smooth and has a broad-based rounded to acute apical horn and two acute to broad rounded antapical horns. The epicyst lacks shoulders, and has a concave margin. The area between the antapical horns has a moderately concave curvature. The endophragm is smooth and subcircular to oval in ambital view. The peri- and endophragm are often in contact laterally. The archaeopyle type is I(2) and is latideltaform with Transversal Archaeopyle Index (TAI) c. 0.70. The paracingulum is not indicated. The parasulcus is often indicated by a longitudal fold in the periphragm. Apart from the archaeopyle and the parasulcus no other paratabulation is present.
Dimensions:holotyperange
length of pericyst96 Ám87(95)104 Ám
width of pericyst61 Ám55(61)73 Ám
length of endophragm55 Ám55(58)61 Ám
width of endophragm55 Ám52(58)64 Ám
Specimens measured: 12
Affinities:
Schioler, 1993, p.110: Isabelidinium majae differs from all other species of Isabelidinium by being almost axially symmetrical and having a lati-deltaform periarchaeopyle with a TAI considerably higher than 0.5. These characters are typical of the genus Deflandrea Eisenack 1938 emend. Lentin and Williams 1978, but as the new species lacks any signs of a paracingulum, referral to the latter genus is precluded. Isabelidinium cooksoniae (Alberti 1959) Lentin and Williams 1977 differs from the new species in having shoulders or at least a convex epicystal outline, a reduced right antapical horn, and a thetaform to omegaform archaeopyle. Isabelidinium glabrum (Cookson and Eisenack 1969) Lentin and Williams 1977 differs in having an almost biconical ambitus, and a TAI around 0.46 as well as a reduced right antapical horn. Isabelidinium bakeri (Deflandre and Cookson 1955) Lentin and Williams 1977 lacks a pronounced left antapical horn, but differs from 1. majae sp. nov. in being widely fusiform, and having a narrow archaeopyle with a TAI around 0.44. Isabelidinium pelucidum (Deflandre and Cookson 1955) Lentin and Williams 1977 has an elongate ovale ambitus and a distinct hexagonal archaeopyle. Isabelidinium belfastense (Cookson and Eisenack 1961) Lentin and Williams 1977 and Isabelidinium greenense Marshall 1990 differs from the new species in archaeopyle-shape and in having antapical horns of different size. I. belfastense furthermore differs in having distinct apical and antapical granulation on the pericyst, and I. greenense has abundant fine perforations surrounding the horns. Manumiella? cretacea (Cookson 1956) Bujak and Davies 1983 is smaller than I. majae and has an almost circular ambitus and a TAI around 0.38. Camera lucida tracings of the ambital outline of the new species are shown in text-fig. 4.
Holotype: Schioler, 1993, pl.1, fig.1, text-fig.4a
Paratype: Schioler, 1993
Locus typicus: Well M-lOx, depth 1973.0m, Dan Field, Danish North Sea
Stratum typicum: Latest Maastrichtian
Original diagnosis: Schioler, 1993, p.108
A cavate peridinioid cyst with a smooth endo- and periphragm without indications of paracingulum. The ambitus shows overall axial symmetry. The periarcheopyle is lati-deltaform.
Original description: Schioler, 1993, p.108
Cavate peridinioid cyst. Cyst outline is almost bilateral symmetric in ambital view. The periphragm is smooth and has a broad-based rounded to acute apical horn and two acute to broad rounded antapical horns. The epicyst lacks shoulders, and has a concave margin. The area between the antapical horns has a moderately concave curvature. The endophragm is smooth and subcircular to oval in ambital view. The peri- and endophragm are often in contact laterally. The archaeopyle type is I(2) and is latideltaform with Transversal Archaeopyle Index (TAI) c. 0.70. The paracingulum is not indicated. The parasulcus is often indicated by a longitudal fold in the periphragm. Apart from the archaeopyle and the parasulcus no other paratabulation is present.
Dimensions:holotyperange
length of pericyst96 Ám87(95)104 Ám
width of pericyst61 Ám55(61)73 Ám
length of endophragm55 Ám55(58)61 Ám
width of endophragm55 Ám52(58)64 Ám
Specimens measured: 12
Affinities:
Schioler, 1993, p.110: Isabelidinium majae differs from all other species of Isabelidinium by being almost axially symmetrical and having a lati-deltaform periarchaeopyle with a TAI considerably higher than 0.5. These characters are typical of the genus Deflandrea Eisenack 1938 emend. Lentin and Williams 1978, but as the new species lacks any signs of a paracingulum, referral to the latter genus is precluded. Isabelidinium cooksoniae (Alberti 1959) Lentin and Williams 1977 differs from the new species in having shoulders or at least a convex epicystal outline, a reduced right antapical horn, and a thetaform to omegaform archaeopyle. Isabelidinium glabrum (Cookson and Eisenack 1969) Lentin and Williams 1977 differs in having an almost biconical ambitus, and a TAI around 0.46 as well as a reduced right antapical horn. Isabelidinium bakeri (Deflandre and Cookson 1955) Lentin and Williams 1977 lacks a pronounced left antapical horn, but differs from 1. majae sp. nov. in being widely fusiform, and having a narrow archaeopyle with a TAI around 0.44. Isabelidinium pelucidum (Deflandre and Cookson 1955) Lentin and Williams 1977 has an elongate ovale ambitus and a distinct hexagonal archaeopyle. Isabelidinium belfastense (Cookson and Eisenack 1961) Lentin and Williams 1977 and Isabelidinium greenense Marshall 1990 differs from the new species in archaeopyle-shape and in having antapical horns of different size. I. belfastense furthermore differs in having distinct apical and antapical granulation on the pericyst, and I. greenense has abundant fine perforations surrounding the horns. Manumiella? cretacea (Cookson 1956) Bujak and Davies 1983 is smaller than I. majae and has an almost circular ambitus and a TAI around 0.38. Camera lucida tracings of the ambital outline of the new species are shown in text-fig. 4.