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Cyclonephelium distinctum ssp. distinctum
Cyclonephelium distinctum ssp. distinctum
Autonym.
Now Circulodinium distinctum ssp. distinctum. Originally Cyclonephelium dictinctum ssp. distinctum, subsequently (and now) Circulodinium distinctum ssp. distinctum.
Holotype: Deflandre and Cookson, 1955, pl.2,fig.14
Locus typicus: Gingin, W Australia
Stratum typicum: Senonian
Original description: Deflandre and Cookson, 1955, p. 285-286
Ornamentation typically consisting of numerous short, solid appendages of variable width, the apices of which are either bluntly pointed, capitate, enlarged, or forked; rarely the processes are joined to one another forming short lamellae. They are irregularly disposed, most numerous at the equator and becoming progressively fewer towards the poles, from which they are entirely absent. Surface of shell distinctly punctate.
Sullpemental description: Davey, 1969, p. 166-167
This species is extremely variable, as pointed out by Cookson and Eisenack (1962), and a member of most Cenomanian assemblages studied. The shell, which is always somewhat flattened, may be subcircular to ovoidal in outline and has a smooth or lightly granular shell wall. The regular outline is sometimes broken by an apical protuberance and more rarely by two reduced, antapical horns. The latter are of unequal size and when present the antapical regioll is slightly concave. The bald areas, typical of this genus, may occupy almost all of the ventral and dorsal surfaces of the shell leaving only the peripheral regions to bear processes, or may be practically invisible beneath the encroaching processes. Usually, however, these bald areas are circular to ovoidal in shape and occupy approximately thirty percent of each side of the shell. The processes are usually abundant, extremely variable in form and typically under one-third of the shell width in length. They are solid and usually widen distally and proximally, may be fine or taeniate, and are often distally bifurcate. The bases of the processes are occasionally thickened and rarely a line of thickening on the shell surface joins one process with a neighbouring one. Equally rarely, and only when the processes are broad, they may be joined distally. A large apical archaeopyle is always present. This is angular, possesses a pronounced zigzag margin and on the ventral surface usually a relatively deep sulcal notch. Although the archaeopyle is always discernible, the operculum is sometimes still attached. It then behaved as a lid, returning to its original position after the escape of the encysted organism.
Range of observed specimens: height of shell (operculum absent) 41 (54.5) 82 Ám width 48 (61.8) 81 Ám, maximum length of the processes 4 (10.7) 21 Ám.
Affinities:
Davey, 1969, p. 167: C. distinctum appears to be extremely variable, and specimens showing extremes in variation sometimes appear to be transitional to other species.
Cookson and Eisenack, 1974, p.74
As shown by us, in particular in our 1962 paper, the C. distinctum is a greatly varying species. This becomes again apparent, mainly in the Balcatta bore. An extreme form is the specimen figured in Figure 7. We do not consider it as appropriate to separate further variants on the basis of the more or less developed processes.The processes occasionally extend very far from the margin of the shell toward the middle. Since, on one and the same specimen, they can moreover greatly vary in form, a close relationship to the Heterosphaeridium heteracanthum (Defl. & Cooks. 1955) seems to be involved here.
Autonym.
Now Circulodinium distinctum ssp. distinctum. Originally Cyclonephelium dictinctum ssp. distinctum, subsequently (and now) Circulodinium distinctum ssp. distinctum.
Holotype: Deflandre and Cookson, 1955, pl.2,fig.14
Locus typicus: Gingin, W Australia
Stratum typicum: Senonian
Original description: Deflandre and Cookson, 1955, p. 285-286
Ornamentation typically consisting of numerous short, solid appendages of variable width, the apices of which are either bluntly pointed, capitate, enlarged, or forked; rarely the processes are joined to one another forming short lamellae. They are irregularly disposed, most numerous at the equator and becoming progressively fewer towards the poles, from which they are entirely absent. Surface of shell distinctly punctate.
Sullpemental description: Davey, 1969, p. 166-167
This species is extremely variable, as pointed out by Cookson and Eisenack (1962), and a member of most Cenomanian assemblages studied. The shell, which is always somewhat flattened, may be subcircular to ovoidal in outline and has a smooth or lightly granular shell wall. The regular outline is sometimes broken by an apical protuberance and more rarely by two reduced, antapical horns. The latter are of unequal size and when present the antapical regioll is slightly concave. The bald areas, typical of this genus, may occupy almost all of the ventral and dorsal surfaces of the shell leaving only the peripheral regions to bear processes, or may be practically invisible beneath the encroaching processes. Usually, however, these bald areas are circular to ovoidal in shape and occupy approximately thirty percent of each side of the shell. The processes are usually abundant, extremely variable in form and typically under one-third of the shell width in length. They are solid and usually widen distally and proximally, may be fine or taeniate, and are often distally bifurcate. The bases of the processes are occasionally thickened and rarely a line of thickening on the shell surface joins one process with a neighbouring one. Equally rarely, and only when the processes are broad, they may be joined distally. A large apical archaeopyle is always present. This is angular, possesses a pronounced zigzag margin and on the ventral surface usually a relatively deep sulcal notch. Although the archaeopyle is always discernible, the operculum is sometimes still attached. It then behaved as a lid, returning to its original position after the escape of the encysted organism.
Range of observed specimens: height of shell (operculum absent) 41 (54.5) 82 Ám width 48 (61.8) 81 Ám, maximum length of the processes 4 (10.7) 21 Ám.
Affinities:
Davey, 1969, p. 167: C. distinctum appears to be extremely variable, and specimens showing extremes in variation sometimes appear to be transitional to other species.
Cookson and Eisenack, 1974, p.74
As shown by us, in particular in our 1962 paper, the C. distinctum is a greatly varying species. This becomes again apparent, mainly in the Balcatta bore. An extreme form is the specimen figured in Figure 7. We do not consider it as appropriate to separate further variants on the basis of the more or less developed processes.The processes occasionally extend very far from the margin of the shell toward the middle. Since, on one and the same specimen, they can moreover greatly vary in form, a close relationship to the Heterosphaeridium heteracanthum (Defl. & Cooks. 1955) seems to be involved here.