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Eisenackia margarita
Eisenackia margarita (Harland, 1979a, p.29,31,33, pl.1, figs.1-12; pl.2, figs.1-10) Quattrocchio and Sarjeant, 2003, p.146.
NOW Alisocysta. Originally Agerasphaera (generic name illegitimate), subsequently (and now) Alisocysta, thirdly Eisenackia.
Taxonomic junior synonym: Alisocysta rugolirata, according to Damassa and Harland in Lentin and Williams (1989, p.10).
Holotype: Harland, 1979a, pl.1, figs.5-6; pl.2, figs.5-6; Fauconnier and Masure, 2004, pl.2, fig.1.
Age: Late Paleocene.
(Harland, 1979a):
1961 Eisenackia crassitabulata Deflandre et Cookson; Alberti, 32, pl.3, fig.19.
1976 Eisenackia circumtabulata Drugg; Schumacker-Lambry and Chateauneuf, pl.I, figs. 1, 2.
?1976 Eisenackia circumtabulata Drugg; Gruas-Cavagnetto, pl.1, figs.l--2.
1977 Eisenackia sp. aff. E. circumtabulata Drugg; Harris, pl.9, figs.8--11.
Derivation of name: Latin, margarita - pearl, with reference to the beaded, like a string of pearls, appearance at the bases of the penitabular membranes.
Diagnosis: Ovoidal cyst with two closely adpressed wall layers and a smooth to microreticulate or micropunctate ornamentation. Paratabulation, ?pr, 4', 6", 6c, 4s, lp, 6'", l""; 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.
Dimensions: Holotype: Length 44.0 µm, breadth 40.0 µm. Range: Length 34.0-(41.64)-44.0 µm, breadth 36.0-(40.0)-46.0 µm. Eleven specimens measured.
Description: Epicyst more conical than the hemispheroidal hypocyst. A single complete specimen shows the rounded nature of the apex (Plate II, 3, 4). Wall layers are closely adjoined with a surface ornamentation varying from smooth to microreticulate or micropunctate. The cyst wall is up to 2.0 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 to 10.0 µm (on Plate I compare figs.5, 6 with figs.ll, 12) 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 (Fig.2). 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 (Plate II, 2, 3 and 10) 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 (see Plate II, 2) 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. Archeopyle 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.
Holotype: Specimen MPK 2107, Plate I, 5, 6 and Plate II, 5, 6.
Type horizon: Thanet Sands, Thanetian (Paleocene), 38.0--39.0 m depth in IGS Stanford-le-Hope Borehole, Essex, England.
Variation: This species varies in overall shape; from elongate to squat (compare Plate I, 7 with Plate II, 10), and in the height of the penitabular membranes from low (Plate I, 9, 10) to quite high (Plate II, 8, 9). The beading effect at the base of the penitabular membrane, although always present, may be more strongly developed on some specimens than on others.
Comparison: Agerasphaera margarita has been described previously as Eisenackia crassitabulata by Alberti (1961), as E. circumtabulata by Schumacker-Lambry and Chateauneuf (1976) and as E. sp. aff. E. circumtabulata by Harris (1977). In all cases their photographs clearly show the diagnostic beading at the base of the penitabular membranes. 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 the paratabulation and by lacking the characteristic beading.
Remarks: McLean (1974) in describing Hystrichokolpoma mentitum may have misinterpreted its process structure and his species may be an extreme example in the morphological range of the present species, i.e. in having exceptionally high penitabular membranes (15.0 pm), but unfortunately, McLean recovered only three specimens. The U-shaped partitions that are mentioned as characteristic of the postcingular processes may be similar in structure to the beading and thickening described for A. margarita.
NOW Alisocysta. Originally Agerasphaera (generic name illegitimate), subsequently (and now) Alisocysta, thirdly Eisenackia.
Taxonomic junior synonym: Alisocysta rugolirata, according to Damassa and Harland in Lentin and Williams (1989, p.10).
Holotype: Harland, 1979a, pl.1, figs.5-6; pl.2, figs.5-6; Fauconnier and Masure, 2004, pl.2, fig.1.
Age: Late Paleocene.
(Harland, 1979a):
1961 Eisenackia crassitabulata Deflandre et Cookson; Alberti, 32, pl.3, fig.19.
1976 Eisenackia circumtabulata Drugg; Schumacker-Lambry and Chateauneuf, pl.I, figs. 1, 2.
?1976 Eisenackia circumtabulata Drugg; Gruas-Cavagnetto, pl.1, figs.l--2.
1977 Eisenackia sp. aff. E. circumtabulata Drugg; Harris, pl.9, figs.8--11.
Derivation of name: Latin, margarita - pearl, with reference to the beaded, like a string of pearls, appearance at the bases of the penitabular membranes.
Diagnosis: Ovoidal cyst with two closely adpressed wall layers and a smooth to microreticulate or micropunctate ornamentation. Paratabulation, ?pr, 4', 6", 6c, 4s, lp, 6'", l""; 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.
Dimensions: Holotype: Length 44.0 µm, breadth 40.0 µm. Range: Length 34.0-(41.64)-44.0 µm, breadth 36.0-(40.0)-46.0 µm. Eleven specimens measured.
Description: Epicyst more conical than the hemispheroidal hypocyst. A single complete specimen shows the rounded nature of the apex (Plate II, 3, 4). Wall layers are closely adjoined with a surface ornamentation varying from smooth to microreticulate or micropunctate. The cyst wall is up to 2.0 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 to 10.0 µm (on Plate I compare figs.5, 6 with figs.ll, 12) 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 (Fig.2). 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 (Plate II, 2, 3 and 10) 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 (see Plate II, 2) 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. Archeopyle 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.
Holotype: Specimen MPK 2107, Plate I, 5, 6 and Plate II, 5, 6.
Type horizon: Thanet Sands, Thanetian (Paleocene), 38.0--39.0 m depth in IGS Stanford-le-Hope Borehole, Essex, England.
Variation: This species varies in overall shape; from elongate to squat (compare Plate I, 7 with Plate II, 10), and in the height of the penitabular membranes from low (Plate I, 9, 10) to quite high (Plate II, 8, 9). The beading effect at the base of the penitabular membrane, although always present, may be more strongly developed on some specimens than on others.
Comparison: Agerasphaera margarita has been described previously as Eisenackia crassitabulata by Alberti (1961), as E. circumtabulata by Schumacker-Lambry and Chateauneuf (1976) and as E. sp. aff. E. circumtabulata by Harris (1977). In all cases their photographs clearly show the diagnostic beading at the base of the penitabular membranes. 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 the paratabulation and by lacking the characteristic beading.
Remarks: McLean (1974) in describing Hystrichokolpoma mentitum may have misinterpreted its process structure and his species may be an extreme example in the morphological range of the present species, i.e. in having exceptionally high penitabular membranes (15.0 pm), but unfortunately, McLean recovered only three specimens. The U-shaped partitions that are mentioned as characteristic of the postcingular processes may be similar in structure to the beading and thickening described for A. margarita.