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Limbicysta pediformis
Limbicysta pediformis Marshall 1989
Acritarch genus.
Holotype. Marshall 1989: Plate 1, figs. 1-5.
Locus typicus: Gippsland Basin, Southeastern Australia
Stratum typicum: Late Cretaceous
Description. Marshall 1989, p. 32, 34
Cysts modified by a weak to distinct middorsal bulge that is often flattened to form a lateral fold. Dorsoventral outline generally equidimensional, central body subpentagonal with apices extended to form two antapical, two lateral, and one apical horn. Horns long, slender with nearly straight to concave sides; margins between horns concave. Apical horn strongly flared distally, bifurcate, branches with rounded tips. Lateral and antapical horns of similar length, but narrower than apical horn. Tips of antapical horns truncated and usually with rounded projections of variable shape along distal margins. Lateral horns flared distally, bifurcate: branches usually similar to those on apical horn, occasionally also bearing rounded projections similar to those on antapical horns. Crest of lateral fold marking the middorsal bulge occasionally merges with a faint groove extending along middle of each lateral horn. Autophragm thins markedly along margins between horns, occasionally split apart parallel to cyst outline in these areas. Autophragm 0.3-0.4 Ám thick elsewhere around periphery, and of uniform thickness or becoming thickened middorsally and midventrally; surface smooth, usually markedly crumpled, and bearing numerous, irregularly spaced perforations 0.5-2.0 Ám in diameter. Parasulcal region suggested by two longitudinal folds which vary from being barely discernible to extending over much of the cyst length. Folds most widely spaced equatorially, and occasionally intersect midpoint of
antapical margin which can be extended to define a rounded peak (Text-Figure 6E).
Size. Autocyst length 134(176)216 Ám, width 154(175)210 Ám; 15 specimens measured.
Discussion. Marshall 1989, p. 32, 34
The splits parallelling the cyst outline could be identified on all specimens examined. On occasional examples, the midventral surface is marked by a small area of thickening that may represent a flagellar marking. The most variable features of the species are ( I ) the terminal furcation of the apical and lateral horns and (2) the development of the lateral fold on the dorsal surface and the longitudinal folds on the ventral surface.
Comparison. Marshall 1989, p. 32, 34
The taxon is chacterized by its subpentagonal central body that has the apices extended to form two antapical, two lateral, and one apical horn.
Occurrence. Cook Cruise sample C4/87 21DDa.
Acritarch genus.
Holotype. Marshall 1989: Plate 1, figs. 1-5.
Locus typicus: Gippsland Basin, Southeastern Australia
Stratum typicum: Late Cretaceous
Description. Marshall 1989, p. 32, 34
Cysts modified by a weak to distinct middorsal bulge that is often flattened to form a lateral fold. Dorsoventral outline generally equidimensional, central body subpentagonal with apices extended to form two antapical, two lateral, and one apical horn. Horns long, slender with nearly straight to concave sides; margins between horns concave. Apical horn strongly flared distally, bifurcate, branches with rounded tips. Lateral and antapical horns of similar length, but narrower than apical horn. Tips of antapical horns truncated and usually with rounded projections of variable shape along distal margins. Lateral horns flared distally, bifurcate: branches usually similar to those on apical horn, occasionally also bearing rounded projections similar to those on antapical horns. Crest of lateral fold marking the middorsal bulge occasionally merges with a faint groove extending along middle of each lateral horn. Autophragm thins markedly along margins between horns, occasionally split apart parallel to cyst outline in these areas. Autophragm 0.3-0.4 Ám thick elsewhere around periphery, and of uniform thickness or becoming thickened middorsally and midventrally; surface smooth, usually markedly crumpled, and bearing numerous, irregularly spaced perforations 0.5-2.0 Ám in diameter. Parasulcal region suggested by two longitudinal folds which vary from being barely discernible to extending over much of the cyst length. Folds most widely spaced equatorially, and occasionally intersect midpoint of
antapical margin which can be extended to define a rounded peak (Text-Figure 6E).
Size. Autocyst length 134(176)216 Ám, width 154(175)210 Ám; 15 specimens measured.
Discussion. Marshall 1989, p. 32, 34
The splits parallelling the cyst outline could be identified on all specimens examined. On occasional examples, the midventral surface is marked by a small area of thickening that may represent a flagellar marking. The most variable features of the species are ( I ) the terminal furcation of the apical and lateral horns and (2) the development of the lateral fold on the dorsal surface and the longitudinal folds on the ventral surface.
Comparison. Marshall 1989, p. 32, 34
The taxon is chacterized by its subpentagonal central body that has the apices extended to form two antapical, two lateral, and one apical horn.
Occurrence. Cook Cruise sample C4/87 21DDa.