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Cannosphaeropsis australis
Cannosphaeropsis australis, Riding and Helby, 2001h, p. 227,229, figs.1A-I.
Holotype: Riding and Helby, 2001h, figs.1D-F.
Holotype and type locality: Figs 1D-F, CPC 35775, from ditch cuttings in Peak-1 well between 1493.53m and 1496.58m. Note that the holotype and topoypes are caved into the Jurassic, upper Wanaea clathrate Zone (6bi).
Stratigraphical distribution: Cannosphaeropsis australis characterizes the late Aptian to late Albian, ranging from the lower Diconodinium davidii Zone (2biic) to the lowermost Pseudoceratium ludbrookiae Zone (1biii) in offshore north-western Australia and Papua New Guinea.
Age: late Aptian-late Albian.
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Original description: [Riding and Helby, 2001h]:
Description:
An intermediate sized species of Cannosphaeropsis with a diaphanous, thin-walled (<0.25 µm), subspherical to elongate ellipsoidal autophragmal body. The autophragm is roughened and undulose. The autophragm is not observed in all specimens. The cyst body is surrounded by thin, ribbon-like, parasutural ectophragmal trabeculae, which bear spiniferate, short, solid, distally pointed processes. This ectophragmal parasutural network is slightly flattened in a polar direction and does not appear to be connected to the cyst body. The parasutural strands of ectophragm are essentially parallel-sided, occasionally having longitudinal striae, varying between 1 and 3 µm in width; the vast majority being between 2 and 3 µm.
At the gonal points, three spines emerge from the trabeculae; intergonally, normally two, occasionally three, pairs of spines per main paraplate boundary emerge. The spines vary from 2 and 4 µm in length with most being between 2 and 3µm. The gonal spines each bisect the angle between two trabeculae and thus point approximately toward the centres of the three adjacent paraplates. The intergonal spines are inserted at right angles to the trabeculum.
A standard sexiform gonyaulacalean paratabulation pattern is indicated. The paratabulation formula appears to be 4’, 6”, 6c, 6”’, 1p, 1””, Xs.
Dimensions: (µm; n=31; including spines where appropriate):
Min. (Mean) Max.
Length of cyst: 62 (67) 71.
Width of cyst in lateral view: 79 (89) 97.
Dorsoventral width of cyst in polar view: 60 (77) 92.
Lateral width of cyst in polar view: 65 (77) 95.
Maximum dimension of central body: 21 (30) 40.
The measured specimens are from a sidewall core sample in Cornea-1 well at 801.10m and from ditch cuttings in Peak-1 well between 1493.53m and 1496.58m.
Remarks:
This distinctive species of Cannosphaeropsis is observed commonly in polar view due to its slight polar flattening; there is no significant dorsoventral flattening. This means that the paracingular trabeculae are normally at the periphery of the cyst and often difficult to observe in detail. When the anterior and posterior paracingular trabeculae are observed, the distance between them, reflecting the height of the box-like paracingular paraplates, is around 7-10 µm. No connecting processes have been observed between the cyst body and the ectophragmal trabeculum. The ectophragm may be distorted, resulting in size differences. The spiniferites-like spine arrangement on the ectophragm is the most characteristic feature of Cannosphaeropsis australis.
Affinities:
Cannosphaeropsis australis differs from other species of Cannosphaeropsis by its elongate cyst body with its characteristic rough, irregular, almost amorphous autophragm and its apparent lack of processes between the autophragm and ectophragm. The most similar taxon is the genotype, Cannosphaeropsis utinensis. However, C. utinensis has occasional processes between the cyst body and the ectophragm (normally close to the as/1’paraplate boundary and on the 4”paraplate), the parasutural trabeculae are much thinner and the spiniferate denticles significantly longer (O. Wetzel, 1933). Cannosphaeropsis passio de Verteuil & Norris 1996 also resembles C. australis. However, the cyst body in C. passio is alveolate and the trabeculae are connected to the cyst body by processes in the parasulcal paraplate series (de Verteuil & Norris, 1996). Cannosphaeropsis australis differs from Hapsocysta peridictya (Cookson & Eisenack 1960) Davey 1979 by virtue of its gonal and intergonal psines and the lack of demonstrable connection of the central body to the trabeculum.
Holotype: Riding and Helby, 2001h, figs.1D-F.
Holotype and type locality: Figs 1D-F, CPC 35775, from ditch cuttings in Peak-1 well between 1493.53m and 1496.58m. Note that the holotype and topoypes are caved into the Jurassic, upper Wanaea clathrate Zone (6bi).
Stratigraphical distribution: Cannosphaeropsis australis characterizes the late Aptian to late Albian, ranging from the lower Diconodinium davidii Zone (2biic) to the lowermost Pseudoceratium ludbrookiae Zone (1biii) in offshore north-western Australia and Papua New Guinea.
Age: late Aptian-late Albian.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Riding and Helby, 2001h]:
Description:
An intermediate sized species of Cannosphaeropsis with a diaphanous, thin-walled (<0.25 µm), subspherical to elongate ellipsoidal autophragmal body. The autophragm is roughened and undulose. The autophragm is not observed in all specimens. The cyst body is surrounded by thin, ribbon-like, parasutural ectophragmal trabeculae, which bear spiniferate, short, solid, distally pointed processes. This ectophragmal parasutural network is slightly flattened in a polar direction and does not appear to be connected to the cyst body. The parasutural strands of ectophragm are essentially parallel-sided, occasionally having longitudinal striae, varying between 1 and 3 µm in width; the vast majority being between 2 and 3 µm.
At the gonal points, three spines emerge from the trabeculae; intergonally, normally two, occasionally three, pairs of spines per main paraplate boundary emerge. The spines vary from 2 and 4 µm in length with most being between 2 and 3µm. The gonal spines each bisect the angle between two trabeculae and thus point approximately toward the centres of the three adjacent paraplates. The intergonal spines are inserted at right angles to the trabeculum.
A standard sexiform gonyaulacalean paratabulation pattern is indicated. The paratabulation formula appears to be 4’, 6”, 6c, 6”’, 1p, 1””, Xs.
Dimensions: (µm; n=31; including spines where appropriate):
Min. (Mean) Max.
Length of cyst: 62 (67) 71.
Width of cyst in lateral view: 79 (89) 97.
Dorsoventral width of cyst in polar view: 60 (77) 92.
Lateral width of cyst in polar view: 65 (77) 95.
Maximum dimension of central body: 21 (30) 40.
The measured specimens are from a sidewall core sample in Cornea-1 well at 801.10m and from ditch cuttings in Peak-1 well between 1493.53m and 1496.58m.
Remarks:
This distinctive species of Cannosphaeropsis is observed commonly in polar view due to its slight polar flattening; there is no significant dorsoventral flattening. This means that the paracingular trabeculae are normally at the periphery of the cyst and often difficult to observe in detail. When the anterior and posterior paracingular trabeculae are observed, the distance between them, reflecting the height of the box-like paracingular paraplates, is around 7-10 µm. No connecting processes have been observed between the cyst body and the ectophragmal trabeculum. The ectophragm may be distorted, resulting in size differences. The spiniferites-like spine arrangement on the ectophragm is the most characteristic feature of Cannosphaeropsis australis.
Affinities:
Cannosphaeropsis australis differs from other species of Cannosphaeropsis by its elongate cyst body with its characteristic rough, irregular, almost amorphous autophragm and its apparent lack of processes between the autophragm and ectophragm. The most similar taxon is the genotype, Cannosphaeropsis utinensis. However, C. utinensis has occasional processes between the cyst body and the ectophragm (normally close to the as/1’paraplate boundary and on the 4”paraplate), the parasutural trabeculae are much thinner and the spiniferate denticles significantly longer (O. Wetzel, 1933). Cannosphaeropsis passio de Verteuil & Norris 1996 also resembles C. australis. However, the cyst body in C. passio is alveolate and the trabeculae are connected to the cyst body by processes in the parasulcal paraplate series (de Verteuil & Norris, 1996). Cannosphaeropsis australis differs from Hapsocysta peridictya (Cookson & Eisenack 1960) Davey 1979 by virtue of its gonal and intergonal psines and the lack of demonstrable connection of the central body to the trabeculum.