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Alisocysta margarita
Alisocysta margarita, (Harland, 1979), Harland, 1979
Originally Agerasphaera (generic name illegitimate), subsequently (and now) Alisocysta, thirdly Eisenackia. Fensome et al. (in press) retained this species in Alisocysta.
Holotype: Harland, 1979a, pl.1, figs.5–6; pl.2, figs.5–6; Fauconnier and Masure, 2004, pl.2, fig.1.
Locus typicus: Essex, England
Stratum typicum: Paleocene
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Original description as Agerasphaera margarita: [Harland, 1979, p. 29-31]:
Diagnosis:
Ovoidal cyst with two closely adpressed wall layers and a smooth to microreticulate or micropunctate ornamentation.
Paratabulation, ?pr, 4', 6'',6c, 4s, 1p, 6''', 1''''; paraplates outlined by low to high thin, membranous, penitabular crests. Contact between the membranes and cyst wall marked by thickenings in the periphragm which give the appearance of beads in optical section.
Archeopyle apical formed by the detachment of the four apical plates which form a single opercular piece, type A.
Description:
Epicyst more conical than the hemispheroidal hypocyst. A single complete specimen shows the rounded nature of the apex. Wall layers are closely adjoined with a surface ornamentation varying from smooth to microreticulate or micropunctate. The cyst wall is up to 2 µm thick but only periphragm makes up the smooth to micropunctate penitabular membranes that outline the paratabulation. The membranes vary in height from 3.0-10.0 µm and have finely serrate or smooth distal margins, and are never closed distally. Structural thickenings occur at the bases of the membranes where they are in contact with the main body of the cyst. The thickenings also extend distally into the membranes and presumably help in their support. In optical section these give a beaded appearance, similar to a string of pearls, to the bases of the membranes. Paratabulation is conspicuous, with four apical paraplates (and probably an apical closing paraplate), six precingular paraplates of trapezoidal shape, and six elongate- rectangular cingular paraplates. The paracingulum takes the form of a laevo-rotatory helicoid, is not indented, and may be displaced ventrally by a distance equivalent to its own width. The parasulcus is conspicuous and consists of four paraplates; an elongate-rectangular anterior sulcal paraplate (as); a triangular right accessory sulcal paraplate (ra); a rectangular right sulcal paraplate (rs) and a trapezoidal posterior sulcal paraplate (ps). The postcingular series consists of six paraplates generally of squat trapezoidal shape, except for 6''' which is triangular. In addition there is one posterior intercalary paraplate and a single antapical paraplate. The broad areas between the plates are not indented but occasionally differ in their ornament. They are usually somewhat smoother than the intratabular area which may have random thickenings akin to those at the bases of the penitabular membrane.
Archaeopyle apical formed by the loss of the four apical paraplates as a single opercular piece, a distinct parasulcal notch is often seen and presumably apical paraplate 1' is more elongate than the other apical paraplates.
Variation:
This species varies in overall shape; from elongate to squat, and in the height of the penitabular membranes from low to quite high. The beading effect at the base of the penitabular membrane, although always present, may be more strongly developed on some specimens than on others.
Dimensions:
Length: 34.0-44.0 µm; breadth 36.0-46.0 µm. Eleven specimens measured.
Affinities: (p. 33):
Agerasphaera circumtabulata differs from A. margarita by having low penitabular membranes and a distinctly ornamented wall. A. margarita is most similar to Hystrichokolpoma mentitum McLean (1974) which differs in possessing box-like, distally closed processes, differences in paratabulation and by lacking the characteristic beading.
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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.
Alisocysta margarita (Harland, 1979a) Harland, 1979a has a smooth to microreticulate or micropunctate ornamentation, with the paraplates outlined by low to high, thin, membranous, penitabular crests. Contact between the membranes and cyst wall marked by thickenings in the periphragm which give the appearance of beads in optical section. Alisocysta circumtabulata differs in having low penitabular membranes and a distinctly ornamented wall. Hystrichokolpoma mentitum has box-like, distally closed processes.
Size: length 34-44 µm, breadth 36-46 µm.
Originally Agerasphaera (generic name illegitimate), subsequently (and now) Alisocysta, thirdly Eisenackia. Fensome et al. (in press) retained this species in Alisocysta.
Holotype: Harland, 1979a, pl.1, figs.5–6; pl.2, figs.5–6; Fauconnier and Masure, 2004, pl.2, fig.1.
Locus typicus: Essex, England
Stratum typicum: Paleocene
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description as Agerasphaera margarita: [Harland, 1979, p. 29-31]:
Diagnosis:
Ovoidal cyst with two closely adpressed wall layers and a smooth to microreticulate or micropunctate ornamentation.
Paratabulation, ?pr, 4', 6'',6c, 4s, 1p, 6''', 1''''; paraplates outlined by low to high thin, membranous, penitabular crests. Contact between the membranes and cyst wall marked by thickenings in the periphragm which give the appearance of beads in optical section.
Archeopyle apical formed by the detachment of the four apical plates which form a single opercular piece, type A.
Description:
Epicyst more conical than the hemispheroidal hypocyst. A single complete specimen shows the rounded nature of the apex. Wall layers are closely adjoined with a surface ornamentation varying from smooth to microreticulate or micropunctate. The cyst wall is up to 2 µm thick but only periphragm makes up the smooth to micropunctate penitabular membranes that outline the paratabulation. The membranes vary in height from 3.0-10.0 µm and have finely serrate or smooth distal margins, and are never closed distally. Structural thickenings occur at the bases of the membranes where they are in contact with the main body of the cyst. The thickenings also extend distally into the membranes and presumably help in their support. In optical section these give a beaded appearance, similar to a string of pearls, to the bases of the membranes. Paratabulation is conspicuous, with four apical paraplates (and probably an apical closing paraplate), six precingular paraplates of trapezoidal shape, and six elongate- rectangular cingular paraplates. The paracingulum takes the form of a laevo-rotatory helicoid, is not indented, and may be displaced ventrally by a distance equivalent to its own width. The parasulcus is conspicuous and consists of four paraplates; an elongate-rectangular anterior sulcal paraplate (as); a triangular right accessory sulcal paraplate (ra); a rectangular right sulcal paraplate (rs) and a trapezoidal posterior sulcal paraplate (ps). The postcingular series consists of six paraplates generally of squat trapezoidal shape, except for 6''' which is triangular. In addition there is one posterior intercalary paraplate and a single antapical paraplate. The broad areas between the plates are not indented but occasionally differ in their ornament. They are usually somewhat smoother than the intratabular area which may have random thickenings akin to those at the bases of the penitabular membrane.
Archaeopyle apical formed by the loss of the four apical paraplates as a single opercular piece, a distinct parasulcal notch is often seen and presumably apical paraplate 1' is more elongate than the other apical paraplates.
Variation:
This species varies in overall shape; from elongate to squat, and in the height of the penitabular membranes from low to quite high. The beading effect at the base of the penitabular membrane, although always present, may be more strongly developed on some specimens than on others.
Dimensions:
Length: 34.0-44.0 µm; breadth 36.0-46.0 µm. Eleven specimens measured.
Affinities: (p. 33):
Agerasphaera circumtabulata differs from A. margarita by having low penitabular membranes and a distinctly ornamented wall. A. margarita is most similar to Hystrichokolpoma mentitum McLean (1974) which differs in possessing box-like, distally closed processes, differences in paratabulation and by lacking the characteristic beading.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Notes:
G.L. Williams short notes on species, Mesozoic-Cenozoic dinocyst course, Urbino, Italy, May 17-22, 1999 - LPP VIEWER CD-ROM 99.5.
Alisocysta margarita (Harland, 1979a) Harland, 1979a has a smooth to microreticulate or micropunctate ornamentation, with the paraplates outlined by low to high, thin, membranous, penitabular crests. Contact between the membranes and cyst wall marked by thickenings in the periphragm which give the appearance of beads in optical section. Alisocysta circumtabulata differs in having low penitabular membranes and a distinctly ornamented wall. Hystrichokolpoma mentitum has box-like, distally closed processes.
Size: length 34-44 µm, breadth 36-46 µm.