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Limbicysta
From Williams et al., 2017:
[Limbicysta, Marshall, 1989, p. 28-32
Acritarch genus.
Tax. jun. syn.: Fentonia (acritarch), according to MacRae et al. (1996, p.1479); and Neofentonia (acritarch), which is a nomenclatural junior synonym of Fentonia.
Type species: Limbicysta pediformis, Marshall, 1989 (pl.1, figs.1–5)]
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Original description: [Marshall, 1989]:
Synopsis:
Cysts compressed; with a middorsal bulge and longitudinal markings along center of ventral surface defining a possible parasulcus. Outline modified by an elongate apical and two lateral horns; antapical margin rounded or bears two elongate horns.
Cysts have one or two wall layers: bi-layered specimens circumcavate to cornucavate, endocyst subcircular to oval in dorsoventral view. Both wall layers smooth, outer layer frequently thins markedly, and may be split apart parallel to cyst outline, in areas around peripheral margin.
Description:
Shape: Cysts compressed dorsoventrally, with a weak to distinct middorsal bulge. Outline modified by an elongate apical and two lateral horns. Horns taper towards midlength; strongly flared and bifurcated distally. Antapical margin rounded or modified by two elongate horns with truncate tips. Cysts generally symmetrical about a longitudinal axis along center of ventral and dorsal surfaces.
Wall Relationships: Cysts single layered or bi-layered. The latter have a subcircular or oval endocyst; are circumcavate or wall layers are in contact at bases of horns and separated elsewhere.
Wall Features: Both wall layers smooth. Periphragm commonly strongly crumpled, can be finely perforate. Periphragm frequently thins markedly, and may have an irregular outline and be split apart parallel to cyst outline, in zones around peripheral margin. Periphragm often thickens slightly towards middorsal and midventral surfaces.
Parasulcus: Suggested by two longitudinal folds on midventral surface. Rarely bearing a thickened area between these folds representing a possible flagellar marking.
Size: Large (after Stover and Evitt, 1978).
Discussion:
Distinctive features common to both species of the genus are: dorsoventral compression; modification of the apical and each lateral margin by an elongate horn with a flared tip; and marked thinning of the outer wall, which may be split apart parallel to the cyst outline, in areas around the periphery of the cyst.
[Limbicysta, Marshall, 1989, p. 28-32
Acritarch genus.
Tax. jun. syn.: Fentonia (acritarch), according to MacRae et al. (1996, p.1479); and Neofentonia (acritarch), which is a nomenclatural junior synonym of Fentonia.
Type species: Limbicysta pediformis, Marshall, 1989 (pl.1, figs.1–5)]
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Original description: [Marshall, 1989]:
Synopsis:
Cysts compressed; with a middorsal bulge and longitudinal markings along center of ventral surface defining a possible parasulcus. Outline modified by an elongate apical and two lateral horns; antapical margin rounded or bears two elongate horns.
Cysts have one or two wall layers: bi-layered specimens circumcavate to cornucavate, endocyst subcircular to oval in dorsoventral view. Both wall layers smooth, outer layer frequently thins markedly, and may be split apart parallel to cyst outline, in areas around peripheral margin.
Description:
Shape: Cysts compressed dorsoventrally, with a weak to distinct middorsal bulge. Outline modified by an elongate apical and two lateral horns. Horns taper towards midlength; strongly flared and bifurcated distally. Antapical margin rounded or modified by two elongate horns with truncate tips. Cysts generally symmetrical about a longitudinal axis along center of ventral and dorsal surfaces.
Wall Relationships: Cysts single layered or bi-layered. The latter have a subcircular or oval endocyst; are circumcavate or wall layers are in contact at bases of horns and separated elsewhere.
Wall Features: Both wall layers smooth. Periphragm commonly strongly crumpled, can be finely perforate. Periphragm frequently thins markedly, and may have an irregular outline and be split apart parallel to cyst outline, in zones around peripheral margin. Periphragm often thickens slightly towards middorsal and midventral surfaces.
Parasulcus: Suggested by two longitudinal folds on midventral surface. Rarely bearing a thickened area between these folds representing a possible flagellar marking.
Size: Large (after Stover and Evitt, 1978).
Discussion:
Distinctive features common to both species of the genus are: dorsoventral compression; modification of the apical and each lateral margin by an elongate horn with a flared tip; and marked thinning of the outer wall, which may be split apart parallel to the cyst outline, in areas around the periphery of the cyst.