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Impagidinium torsium
Impagidinium torsium Stover and Hardenbol, 1994
Impagidinium torsium sp. nov.
Plate 7, Figures 47a-c, 48; Plate 8, Figures 49a-c
Description: Stover and Hardenbol, 1994, p. 36
Cysts proximate, subspherical; autophragm about 1 µm thick, smooth, faintly scabrate, or with a few scattered granulae. Parasutural septa smooth, tapered distally and of uniform height (2.0 to 4.0µm); bases of septa may be finely perforate. The precingular archeopyle, which is offset slightly to the left, has a monoplacoid (paraplate 3""), secate operculum.
Paratabulation gonyaulacoid, expressed by parasutural septa; formula: 3", 6", 6c, 5 """, 1p,1"""", 2-3s. Hypocystal paratabulation pattern standard sexiform. Parasutural septum 1"/4" absent, although a short medial spur projecting apically from the posterior septum of 1" is present on some specimens. Paracingulum laevorotatory and its anterior ends are offset longitudinally by about two cingular widths; ends also aligned longitudinally or have very little transverse separation. Parasulcus inclined posterodextrally, relatively wide (5.5 to 9.5 µm), and widens posteriorly. Posterior sulcal paraplate delimited anteriorly by horizontal transverse septum; rest of parasulcus may be subdivided by inclined medial septum into anterior and medial sulcal paraplates. Specimens are 40 to 45 µm in length and 37 to 42 µm in width.
Comparison
Impagidinium torsium resembles I. dispertitum (Cookson and Eisenack 1965) Stover and Evitt 1978 but differs from it by being smaller, subspherical rather than ellipsoidal and by having very little transverse separation between the ends of the paracingulum and by having an inclined parasulcus. In addition, scattered granulae may be present on specimens of I. torsium.
Types
Holotype: Plate 7, figures 47a-c. Paratypes: Plate 7, figure 48 and Plate 8, figures 49a-c.
All type specimens are from the Boom Composite Section sample at the 8.86 meter level, Sint Niklaas locality.
Occurrence
Impagidinium torsium occurs consistently in the Boom Formations between 2.00 and 11.20 meters in the composite section (Belsele-Waas and Terhagen Members) and is most abundant in samples from and near the S10 horizon. The species was also identified in the three samples from the Ruisbroek Member of the Zelzate Formation in the Doel 14E-194 Well.
Impagidinium torsium sp. nov.
Plate 7, Figures 47a-c, 48; Plate 8, Figures 49a-c
Description: Stover and Hardenbol, 1994, p. 36
Cysts proximate, subspherical; autophragm about 1 µm thick, smooth, faintly scabrate, or with a few scattered granulae. Parasutural septa smooth, tapered distally and of uniform height (2.0 to 4.0µm); bases of septa may be finely perforate. The precingular archeopyle, which is offset slightly to the left, has a monoplacoid (paraplate 3""), secate operculum.
Paratabulation gonyaulacoid, expressed by parasutural septa; formula: 3", 6", 6c, 5 """, 1p,1"""", 2-3s. Hypocystal paratabulation pattern standard sexiform. Parasutural septum 1"/4" absent, although a short medial spur projecting apically from the posterior septum of 1" is present on some specimens. Paracingulum laevorotatory and its anterior ends are offset longitudinally by about two cingular widths; ends also aligned longitudinally or have very little transverse separation. Parasulcus inclined posterodextrally, relatively wide (5.5 to 9.5 µm), and widens posteriorly. Posterior sulcal paraplate delimited anteriorly by horizontal transverse septum; rest of parasulcus may be subdivided by inclined medial septum into anterior and medial sulcal paraplates. Specimens are 40 to 45 µm in length and 37 to 42 µm in width.
Comparison
Impagidinium torsium resembles I. dispertitum (Cookson and Eisenack 1965) Stover and Evitt 1978 but differs from it by being smaller, subspherical rather than ellipsoidal and by having very little transverse separation between the ends of the paracingulum and by having an inclined parasulcus. In addition, scattered granulae may be present on specimens of I. torsium.
Types
Holotype: Plate 7, figures 47a-c. Paratypes: Plate 7, figure 48 and Plate 8, figures 49a-c.
All type specimens are from the Boom Composite Section sample at the 8.86 meter level, Sint Niklaas locality.
Occurrence
Impagidinium torsium occurs consistently in the Boom Formations between 2.00 and 11.20 meters in the composite section (Belsele-Waas and Terhagen Members) and is most abundant in samples from and near the S10 horizon. The species was also identified in the three samples from the Ruisbroek Member of the Zelzate Formation in the Doel 14E-194 Well.