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Cooksoniella sverdrupiana
Cooksoniella sverdrupiana, (Manum, 1963), Williams and Brideaux, 1975
Now Spinidinium. Originally Deflandrea, subsequently (and now) Spinidinium, thirdly Subtilisphaera, fourthly Cooksoniella (combination not validly published).
Holotype: Manum, 1963, pl.2, figs.12-13
Age: Cenomanian
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Original description: [Manum 1963, p. 59-60]:
Diagnosis:
Theca in dorsoventral view roughly rhomboid with the obtuse angles in the equatorial region, and divided into nearly equal parts by a slightly spiral, laevo-rotatory girdle.
Epitheca narrows towards a short, blunt or truncate apical horn. Hypotheca conspicuously asymmetric with a prominent, sharply pointed horn on the left-hand side, and a small bulge suggestive of a horn on the right-hand side. Theca ornamented by spine-like to conical processes up to 3 µm high arranged so as to indicate fields or plates according to the formula 4', 3a, 7", 5"', ?"". The girdle is bordered by discontinuous lines of similar processes.
Archeopyle (2a) elongate and roughly trapezium-shaped.
A capsule of approximately circular outline fills the greater part of the theca.
Description:
The theca-membrane, less than 1 µm thick, is usually more or less folded so that the tabulation indicated by the linearly arranged spines could not be fully obtained from a single specimen. The prominence of the spines varies, usually they are most prominent along the girdle and for some distance on either side of it, thus the precingular and postcingular plates are the ones most easily distinguishable. Although the general shape of the archeopyle is reminiscent of a trapezium, its basic shape is hexagonal with alternating short and long sides. The conspicuous "breaks" in the girdle occur dorsally at some distance on either side of the mid-line, and ventrally more or less close to the lateral margins of the theca. The longitudinal furrow is not clearly outlined. The capsule usually does not quite reach the lateral walls of the theca. The wall of the capsule is less than 1 µm thick, its surface is usually granular.
Dimensions:
Holotype: overall length 94 µm, width 53 µm.
Range: length 51-98 µm, width 35-61 µm. Average of 32 specimens: 77x46 µm.
Affinities/Comments:
D. sverdrupiana is quite distinct from D. scheii in shape and ornamentation, but the two species have certain characters in common which indicate close relationship. The tabulation indicated by the ornamentation in D. sverdrupiana corresponds to that of D. scheii. Furthermore, both species have a laevo-rotatory girdle with "breaks" in identical positions, and the more strongly developed horn is on the left-hand side of the antapex. Of the previously described species of Deflandrea only three need to be compared with D. sverdrupiana. D. pirnaensis Alberti (1959) from German Turonian deposits is comparable with it in size and shape, but differs in having a granular theca-membrane, no breaks in the girdle, and no distinct archeopyle. D. balmei Cookson & Eisenack (1962) from the Upper Cretaceous of Western Australia agrees with D. sverdrupiana in having linearly arranged spines but is much smaller, more rounded in outline, and has no antapical horns. D. echinoidea Cookson & Eisenack (1960), also from the Upper Cretaceous of Western Australia, is similar to D. sverdrupiana in having one prominently developed antapical horn and an ornamentation of spines. However, the theca of D. echinoidea has a more circular outline, the girdle is unbroken, and the spines are longer (up to 5 µm), more numerous and more closely arranged.
Now Spinidinium. Originally Deflandrea, subsequently (and now) Spinidinium, thirdly Subtilisphaera, fourthly Cooksoniella (combination not validly published).
Holotype: Manum, 1963, pl.2, figs.12-13
Age: Cenomanian
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Manum 1963, p. 59-60]:
Diagnosis:
Theca in dorsoventral view roughly rhomboid with the obtuse angles in the equatorial region, and divided into nearly equal parts by a slightly spiral, laevo-rotatory girdle.
Epitheca narrows towards a short, blunt or truncate apical horn. Hypotheca conspicuously asymmetric with a prominent, sharply pointed horn on the left-hand side, and a small bulge suggestive of a horn on the right-hand side. Theca ornamented by spine-like to conical processes up to 3 µm high arranged so as to indicate fields or plates according to the formula 4', 3a, 7", 5"', ?"". The girdle is bordered by discontinuous lines of similar processes.
Archeopyle (2a) elongate and roughly trapezium-shaped.
A capsule of approximately circular outline fills the greater part of the theca.
Description:
The theca-membrane, less than 1 µm thick, is usually more or less folded so that the tabulation indicated by the linearly arranged spines could not be fully obtained from a single specimen. The prominence of the spines varies, usually they are most prominent along the girdle and for some distance on either side of it, thus the precingular and postcingular plates are the ones most easily distinguishable. Although the general shape of the archeopyle is reminiscent of a trapezium, its basic shape is hexagonal with alternating short and long sides. The conspicuous "breaks" in the girdle occur dorsally at some distance on either side of the mid-line, and ventrally more or less close to the lateral margins of the theca. The longitudinal furrow is not clearly outlined. The capsule usually does not quite reach the lateral walls of the theca. The wall of the capsule is less than 1 µm thick, its surface is usually granular.
Dimensions:
Holotype: overall length 94 µm, width 53 µm.
Range: length 51-98 µm, width 35-61 µm. Average of 32 specimens: 77x46 µm.
Affinities/Comments:
D. sverdrupiana is quite distinct from D. scheii in shape and ornamentation, but the two species have certain characters in common which indicate close relationship. The tabulation indicated by the ornamentation in D. sverdrupiana corresponds to that of D. scheii. Furthermore, both species have a laevo-rotatory girdle with "breaks" in identical positions, and the more strongly developed horn is on the left-hand side of the antapex. Of the previously described species of Deflandrea only three need to be compared with D. sverdrupiana. D. pirnaensis Alberti (1959) from German Turonian deposits is comparable with it in size and shape, but differs in having a granular theca-membrane, no breaks in the girdle, and no distinct archeopyle. D. balmei Cookson & Eisenack (1962) from the Upper Cretaceous of Western Australia agrees with D. sverdrupiana in having linearly arranged spines but is much smaller, more rounded in outline, and has no antapical horns. D. echinoidea Cookson & Eisenack (1960), also from the Upper Cretaceous of Western Australia, is similar to D. sverdrupiana in having one prominently developed antapical horn and an ornamentation of spines. However, the theca of D. echinoidea has a more circular outline, the girdle is unbroken, and the spines are longer (up to 5 µm), more numerous and more closely arranged.