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Senoniasphaera rotundata ssp. alveoloata
Senoniasphaera rotundata subsp. alveolata Pearce et al., 2003, p.301–302, pl.2, figs.6–7.
Taxonomic senior synonym: Senoniasphaera turonica, according to Pearce et al. (2011, p.92).
Holotype: Pearce et al., 2003, pl.2, figs.6–7.
Age: early Turonian–early Coniacian.
Original description (Pearce et al., 2003):
Senoniasphaera rotundata (Clarke and Verdier, 1967); emend. Prince et al., 1999, alveolata subsp. nov.; Plate II, figs 6 and 7
Diagnosis: A species of Senoniasphaera with areas of thickened and strongly granular ectophragm possessing invaginations of variable morphology located on both the dorsal and ventral surfaces.
Description: Inner body lenticular to compressed dorso-ventrally, composed of an autophragm that rarely possesses lateral or antapical protrusions; the surface may appear microgranular. The inner body is connected to the outer body by numerous processes, which are short (1-5 µm), narrow at their mid-point and are of variable width (1-2 µm) with a fibrous to densely granulate appearance. They are longest in the antapical and paracingular region where they appear more closely spaced and where the greatest development of the ectocoel occurs. Outer body also lenticular to compressed dorso-ventrally, closely approximates the inner body and is composed of an ectophragm. Areas of thickened ectophragm with dense granular ornamentation are present on the dorsal and ventral surface, which possess invaginations that are rarely greater than 4 Wm in diameter, round to sub-polygonal in shape. These invaginations also have granular ornamentation but which is finer and less dense than the surrounding ectophragm. The thickened ectophragm is arranged laterally across the dorsal surface being absent in the paracingular region, and vertically across the ventral surface, which may reflect the parasulcus and surrounding paraplates. However, the great morphological variability of these densely ornamented regions makes the determination of paraplate relationships problematic. The ectophragm may develop into antapical horns, which if present are of sub-equal length, and lateral horns. The archeopyle is apical, (tA), with a well-developed zigzag margin, the operculum is sometimes adnate but more usually detached. The parasulcal notch is offset. The paracingulum is inferred from the inflation of the ectophragm at the ambitus coinciding with the lateral horns and by the absence of thickened ectophragm on the dorsal surface.
1988 Canningia sp. A, MARSHALL and BATTEN, p. 90; pl. 1, figs. 1 and 2 (lower Turonian, northern
Germany).
1989 Senoniasphaera rotundata, AURISANO, p. 173; pl. 2, fig. 4 (lower Campanian, USA) (Aurisano, 1989).
1992 Senoniasphaera sp. A, SCHIZLER, p. 21; pl. 3, figs.1-8 (upper Turonian^Coniacian, Denmark) (Schioler, 1992).
1997 Senoniasphaera ‘alveolata’, PRINCE, p. 3/82; pl. 4,figs. 10^12; pl. 5, figs. 1 and 2 ( ?upper Turonian-lower Campanian, England, Isle of Wight).
1999 Senoniasphaera rotundata, PRINCE et al., pl. 1, figs. 3 and 7 only.
Dimensions (20 specimens measured):
Inner body (w/l) Range : 43(54.3)66 X 40(46.2)60 µm. Holotype: 56 X46 µm
Outer body (w/l) Range: 51(64.4)80 X 40(55.3)72 µm. Holotype: 67 X 56 Wm
Repository: British Geological Survey, Kingsley Dunham Centre, Keyworth, Nottingham, UK. Holotype number: MPK 12667.
Stratigraphic range: First occurrence datum: lower Turonian (upper Mytiloides labiatus Zone); last occurrence datum: lower Coniacian (lower Micraster cortestudinarium Zone).
Comments: Dinocysts referable to the description given above, are assigned to subspecies level so as not to con£ict with the existing FAD of the species as a useful lower Turonian marker (Foucher, 1983). Specimens from the Banterwick Barn borehole referable to the holotype of Senoniasphaera rotundata are typically of Coniacian age, and are herein referred to as Senoniasphaera rotundata rotundata. More work is required to address the possibility that these subspecies may be a product of ecophenotypic variation.
Taxonomic senior synonym: Senoniasphaera turonica, according to Pearce et al. (2011, p.92).
Holotype: Pearce et al., 2003, pl.2, figs.6–7.
Age: early Turonian–early Coniacian.
Original description (Pearce et al., 2003):
Senoniasphaera rotundata (Clarke and Verdier, 1967); emend. Prince et al., 1999, alveolata subsp. nov.; Plate II, figs 6 and 7
Diagnosis: A species of Senoniasphaera with areas of thickened and strongly granular ectophragm possessing invaginations of variable morphology located on both the dorsal and ventral surfaces.
Description: Inner body lenticular to compressed dorso-ventrally, composed of an autophragm that rarely possesses lateral or antapical protrusions; the surface may appear microgranular. The inner body is connected to the outer body by numerous processes, which are short (1-5 µm), narrow at their mid-point and are of variable width (1-2 µm) with a fibrous to densely granulate appearance. They are longest in the antapical and paracingular region where they appear more closely spaced and where the greatest development of the ectocoel occurs. Outer body also lenticular to compressed dorso-ventrally, closely approximates the inner body and is composed of an ectophragm. Areas of thickened ectophragm with dense granular ornamentation are present on the dorsal and ventral surface, which possess invaginations that are rarely greater than 4 Wm in diameter, round to sub-polygonal in shape. These invaginations also have granular ornamentation but which is finer and less dense than the surrounding ectophragm. The thickened ectophragm is arranged laterally across the dorsal surface being absent in the paracingular region, and vertically across the ventral surface, which may reflect the parasulcus and surrounding paraplates. However, the great morphological variability of these densely ornamented regions makes the determination of paraplate relationships problematic. The ectophragm may develop into antapical horns, which if present are of sub-equal length, and lateral horns. The archeopyle is apical, (tA), with a well-developed zigzag margin, the operculum is sometimes adnate but more usually detached. The parasulcal notch is offset. The paracingulum is inferred from the inflation of the ectophragm at the ambitus coinciding with the lateral horns and by the absence of thickened ectophragm on the dorsal surface.
1988 Canningia sp. A, MARSHALL and BATTEN, p. 90; pl. 1, figs. 1 and 2 (lower Turonian, northern
Germany).
1989 Senoniasphaera rotundata, AURISANO, p. 173; pl. 2, fig. 4 (lower Campanian, USA) (Aurisano, 1989).
1992 Senoniasphaera sp. A, SCHIZLER, p. 21; pl. 3, figs.1-8 (upper Turonian^Coniacian, Denmark) (Schioler, 1992).
1997 Senoniasphaera ‘alveolata’, PRINCE, p. 3/82; pl. 4,figs. 10^12; pl. 5, figs. 1 and 2 ( ?upper Turonian-lower Campanian, England, Isle of Wight).
1999 Senoniasphaera rotundata, PRINCE et al., pl. 1, figs. 3 and 7 only.
Dimensions (20 specimens measured):
Inner body (w/l) Range : 43(54.3)66 X 40(46.2)60 µm. Holotype: 56 X46 µm
Outer body (w/l) Range: 51(64.4)80 X 40(55.3)72 µm. Holotype: 67 X 56 Wm
Repository: British Geological Survey, Kingsley Dunham Centre, Keyworth, Nottingham, UK. Holotype number: MPK 12667.
Stratigraphic range: First occurrence datum: lower Turonian (upper Mytiloides labiatus Zone); last occurrence datum: lower Coniacian (lower Micraster cortestudinarium Zone).
Comments: Dinocysts referable to the description given above, are assigned to subspecies level so as not to con£ict with the existing FAD of the species as a useful lower Turonian marker (Foucher, 1983). Specimens from the Banterwick Barn borehole referable to the holotype of Senoniasphaera rotundata are typically of Coniacian age, and are herein referred to as Senoniasphaera rotundata rotundata. More work is required to address the possibility that these subspecies may be a product of ecophenotypic variation.