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Batiacasphaera subtilis
Batiacasphaera subtilis, Stover and Helby, 1987
Holotype: Stover and Helby, 1987, fig.2A-B
Paratypes: Stover and Helby, 1987
Locus typicus: Exmouth Plateau, W Australia
Stratum typicum: Hauterivian-Barremian
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Original description: [Stover and Helby, 1987, p. 228-230]:
Description:
Cysts subspherical to ellipsoidal, rarely distorted by folding. Autophragm 2 µm to slightly more than 3 µm thick equatorially, thinning gradually toward the poles (Figs 2A,D, 31,K). Outer surface of the autophragm smooth, chagrenate, finely granular, or with low, ill-defined, irregularly shaped projections. Ornamentation most pronounced equatorially, generally decreasing in magnitude and distinctness towards commonly smooth poles (Figs 2A,B, 3G-I). All specimens with some ornamentation in the equatorial area; relatively few sculptured entirely or nearly so (Fig.2E,F).
Archeopyle apical, type [tA], with an angular principal archeopyle suture and a prominent parasulcal notch (Figs 2A-F, 3H,L). Accessory archeopyle sutures typically absent. Operculum usually free, but may be adherent, its constituent paraplates not differentiated on the opercular surface. Indications of a paracingulum and parasulcus lacking, anterior position of the latter implied by the parasulcal notch.
Paratabulation expressed solely by the archeopyle margin whose angulations indicate 6 precingular paraplates. On many specimens, the gabled anterior edges of 1"", 3"", 5" and 6", and the flat edges of 2" and 4"" discernible; however, the peaks of 3"" and 5" frequently less evident than the others (Figs 2B,F, 3A,D,G,I,J-L).
Dimensions:
Specimens, exclusive of opercula, 56 (67)76 µm in length, and 50(59)67 µm in equatorial diameter; 25 specimens measured.
Specimens with opercula about 3-6 µm longer than those without them.
Variability:
Among specimens of Batiacasphaera subtilis a tendency exists for the operculum, upon separation, not to break cleanly and completely along the principal archeopyle suture but rather to take with it portions of some precingular paraplates (Fig.3B) or even split across the operculum (Fig.3C). When either occurs, the resulting opening has an irregular outline with arcuate and/or ragged margins. The ornamentation, regardless of the type or of its distribution on the cysts, is consistently subdued.
Affinities:
Batiacasphaera subtilis and B. euteiches (Davey) Davey 1979 are similar in having relatively thick autophragms and conspicuous parasulcal notches. The ornamentation on B. euteiches is uniformly fine and evenly distributed; in contrast, that on B. subtilis is generally concentrated or developed more markedly in the equatorial area than on the other parts of the cyst. Batiacasphaera subtilis differs further from B. euteiches in having the thickness of the autophragm decrease towards the poles, in lacking accessory archeopyle sutures and in being more elongate (ellipsoidal) and larger than B. euteiches, although the size ranges of the two species overlap slightly. Batiacasphaera crassicingulata (Burger) Helby (1987), which is similar to B. subtilis in having the autophragm thin towards the poles, is smooth rather than ornamented. Future studies may indicate the desirability of combining these two species when the full extent of their variability is determined.
Holotype: Stover and Helby, 1987, fig.2A-B
Paratypes: Stover and Helby, 1987
Locus typicus: Exmouth Plateau, W Australia
Stratum typicum: Hauterivian-Barremian
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Stover and Helby, 1987, p. 228-230]:
Description:
Cysts subspherical to ellipsoidal, rarely distorted by folding. Autophragm 2 µm to slightly more than 3 µm thick equatorially, thinning gradually toward the poles (Figs 2A,D, 31,K). Outer surface of the autophragm smooth, chagrenate, finely granular, or with low, ill-defined, irregularly shaped projections. Ornamentation most pronounced equatorially, generally decreasing in magnitude and distinctness towards commonly smooth poles (Figs 2A,B, 3G-I). All specimens with some ornamentation in the equatorial area; relatively few sculptured entirely or nearly so (Fig.2E,F).
Archeopyle apical, type [tA], with an angular principal archeopyle suture and a prominent parasulcal notch (Figs 2A-F, 3H,L). Accessory archeopyle sutures typically absent. Operculum usually free, but may be adherent, its constituent paraplates not differentiated on the opercular surface. Indications of a paracingulum and parasulcus lacking, anterior position of the latter implied by the parasulcal notch.
Paratabulation expressed solely by the archeopyle margin whose angulations indicate 6 precingular paraplates. On many specimens, the gabled anterior edges of 1"", 3"", 5" and 6", and the flat edges of 2" and 4"" discernible; however, the peaks of 3"" and 5" frequently less evident than the others (Figs 2B,F, 3A,D,G,I,J-L).
Dimensions:
Specimens, exclusive of opercula, 56 (67)76 µm in length, and 50(59)67 µm in equatorial diameter; 25 specimens measured.
Specimens with opercula about 3-6 µm longer than those without them.
Variability:
Among specimens of Batiacasphaera subtilis a tendency exists for the operculum, upon separation, not to break cleanly and completely along the principal archeopyle suture but rather to take with it portions of some precingular paraplates (Fig.3B) or even split across the operculum (Fig.3C). When either occurs, the resulting opening has an irregular outline with arcuate and/or ragged margins. The ornamentation, regardless of the type or of its distribution on the cysts, is consistently subdued.
Affinities:
Batiacasphaera subtilis and B. euteiches (Davey) Davey 1979 are similar in having relatively thick autophragms and conspicuous parasulcal notches. The ornamentation on B. euteiches is uniformly fine and evenly distributed; in contrast, that on B. subtilis is generally concentrated or developed more markedly in the equatorial area than on the other parts of the cyst. Batiacasphaera subtilis differs further from B. euteiches in having the thickness of the autophragm decrease towards the poles, in lacking accessory archeopyle sutures and in being more elongate (ellipsoidal) and larger than B. euteiches, although the size ranges of the two species overlap slightly. Batiacasphaera crassicingulata (Burger) Helby (1987), which is similar to B. subtilis in having the autophragm thin towards the poles, is smooth rather than ornamented. Future studies may indicate the desirability of combining these two species when the full extent of their variability is determined.