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Australisphaera fragilis
Australisphaera fragilis, Harding, 1986
Holotype: Harding 1986, pl.16, fig.6
Type locality: Warlingham borehole, Surrey. England. Sample WM 14I6 ft 6-7 in. (431 ·73 m).
Age: Late Hauterivian
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Original description: [Harding, 1986]:
Diagnosis:
Shape: regularly ceratioid. Horns developed to greater or lesser extent in apical (I horn), cingular (2 horns), and antapical (I or 2 horns) positions. Often only 'bulges' developed.
Phragma: of two closely adpressed layers (see generic diagnosis). 0.5 μm thick, sculpture of short echinae 0.5 μm long or smaller granulae. Paratabulation: only visible as archaeopyle suture, rarely around paracingulum and parasulcus.
Archaeopyle: apical, type (tA), operculum free.
Paracingulum: well developed on cingular horns in which it forms a notched groove. Not expressed in mid-dorsal position.
Parasulcus: occasionally an arcuate depression in mid-ventral position.
Dimension:
Length (less operculum) (40) 47.2 (55) μm, length (including operculum) (55) 60.8 (68) μm, breadth (45) 49.8 (60) μm, 56 (24) specimens.
Remarks:
The extremely thin autophragm of this species means that specimens are rarely found in a good state of preservation. For every five torn or folded cysts there is only one well-preserved example. The apical horn is well developed when present; some specimens have long left antapical horns. A. fragilis can be distinguished from the other species of Australisphaero by its evenly distributed ornamentation and much more regular ceratioid shape.
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Supplemental description:
Batten and Lister, 1988, p. 338, 340:
Description:
Proximate ceratioid cyst, moderately flattened dorsoventrally, possessing 4 or 5 horns; maximum diameter 55(60)68 µm including operculum x 41(54)64 µm (10 specimens), length without operculum 40(50)61 µm (10 specimens).
Apical horn low to fairly prominent, conical, distally rounded; lateral horns developed as slight bulges or extensions of paracingulum; antapical horns also low to moderately prominent, left commonly more strongly developed than right which may be reduced or absent.
Cyst wall extremely thin (<0.5 µm), flimsy, consisting of autophragm only or possibly two closely adpressed layers. A uniformly granular to echinate surface sculpture of very low relief (<0.5 µm) is faintly to clearly discernible at high magnifications under a transmitted light microscope. Paracingulum well-defined towards lateral margins and frequently displays a pronounced distal notch.
Paratabulation also expressed by apical archeopyle, type (tA), and by an angular archeopyle margin, minor splitting along accessory sutures indicating presence of six precingular paraplates and an offset parasulcal notch.
Principal archeopyle suture complete; operculum free.
Remarks:
Numerous specimens of Australisphaera displaying characters that conform to the specific diagnosis of A. fragilis have been recovered from several horizons. Damage or crumpling of the flimsy wall commonly obscures its regular ceratioid outline. Horn-like protuberances of the phragma are nevertheless usually discernible.
It is not possible to confirm Harding's (1986) interpretation of the wall of this species as being composed of two closely adpressed layers; indeed, its extreme flimsiness strongly suggests that it is only an autophragm. Hence, we only tentatively accept his emendation of the genus. Distinctly granulate specimens are less common than weakly sculptured forms. They are considered to be end members of a morphological continuum and not diagnostic of a separate species.
Holotype: Harding 1986, pl.16, fig.6
Type locality: Warlingham borehole, Surrey. England. Sample WM 14I6 ft 6-7 in. (431 ·73 m).
Age: Late Hauterivian
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Harding, 1986]:
Diagnosis:
Shape: regularly ceratioid. Horns developed to greater or lesser extent in apical (I horn), cingular (2 horns), and antapical (I or 2 horns) positions. Often only 'bulges' developed.
Phragma: of two closely adpressed layers (see generic diagnosis). 0.5 μm thick, sculpture of short echinae 0.5 μm long or smaller granulae. Paratabulation: only visible as archaeopyle suture, rarely around paracingulum and parasulcus.
Archaeopyle: apical, type (tA), operculum free.
Paracingulum: well developed on cingular horns in which it forms a notched groove. Not expressed in mid-dorsal position.
Parasulcus: occasionally an arcuate depression in mid-ventral position.
Dimension:
Length (less operculum) (40) 47.2 (55) μm, length (including operculum) (55) 60.8 (68) μm, breadth (45) 49.8 (60) μm, 56 (24) specimens.
Remarks:
The extremely thin autophragm of this species means that specimens are rarely found in a good state of preservation. For every five torn or folded cysts there is only one well-preserved example. The apical horn is well developed when present; some specimens have long left antapical horns. A. fragilis can be distinguished from the other species of Australisphaero by its evenly distributed ornamentation and much more regular ceratioid shape.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Supplemental description:
Batten and Lister, 1988, p. 338, 340:
Description:
Proximate ceratioid cyst, moderately flattened dorsoventrally, possessing 4 or 5 horns; maximum diameter 55(60)68 µm including operculum x 41(54)64 µm (10 specimens), length without operculum 40(50)61 µm (10 specimens).
Apical horn low to fairly prominent, conical, distally rounded; lateral horns developed as slight bulges or extensions of paracingulum; antapical horns also low to moderately prominent, left commonly more strongly developed than right which may be reduced or absent.
Cyst wall extremely thin (<0.5 µm), flimsy, consisting of autophragm only or possibly two closely adpressed layers. A uniformly granular to echinate surface sculpture of very low relief (<0.5 µm) is faintly to clearly discernible at high magnifications under a transmitted light microscope. Paracingulum well-defined towards lateral margins and frequently displays a pronounced distal notch.
Paratabulation also expressed by apical archeopyle, type (tA), and by an angular archeopyle margin, minor splitting along accessory sutures indicating presence of six precingular paraplates and an offset parasulcal notch.
Principal archeopyle suture complete; operculum free.
Remarks:
Numerous specimens of Australisphaera displaying characters that conform to the specific diagnosis of A. fragilis have been recovered from several horizons. Damage or crumpling of the flimsy wall commonly obscures its regular ceratioid outline. Horn-like protuberances of the phragma are nevertheless usually discernible.
It is not possible to confirm Harding's (1986) interpretation of the wall of this species as being composed of two closely adpressed layers; indeed, its extreme flimsiness strongly suggests that it is only an autophragm. Hence, we only tentatively accept his emendation of the genus. Distinctly granulate specimens are less common than weakly sculptured forms. They are considered to be end members of a morphological continuum and not diagnostic of a separate species.