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Williamsidinium banksianum
Williamsidinium banksianum Lentin, 1983
Holotype: Lentin, 1983, pl.1, figs.1a-b; Fensome et al., 1993a, figs.1-2 - p.963.
Locus typicus: Latitude 73¦26"5"N, longitude 123¦56"45"W, Banks Island, Northwest Territories, Canada
Stratum typicum: Maastrichtian
Original diagnosis: Lentin, 1983, p.148,150
Pericyst ambitus rhomboidal to subpentagonal, elongated in an anteroposterior direction. Pericyst prolonged into one apical and two symmetrically placed antapical horns, the right antapical generally reduced or vestigial. The pericyst attains its greatest width in the region of the pericingulum. Cyst dorsoventrally compressed.
Endocyst ambitus circular to ovoidal to rhomboidal in dorsoventral view. May be in contact with pericyst in precingular, cingular and postcingular regions as well as the base of the intercalary paraplates. Apical and antapical pericoels always present. The apical and antapical pericoels may be united by an ambital pericoel.
Thickness of the periphragm variable but usually ca. 1 µm. Surface generally laevigate, occasionally scabrate, granulate, or verrucate. The endophragm rarely exceeds 1 µm and is of constant thickness. Surface generally laevigate.
Paratabulation indeterminate except in the vicinity of the periarcheopyle which indicates a peridinioid style of tabulation. Paracingulum may or may not be well developed, planar or slightly helicoidal, with anterior parasuture only, or anterior and posterior parasuture as a slightly raised ridge or border, with smooth or denticulate margins. The parasulcus is rarely determinable; when visible largely restricted to the hypopericyst. A flagellar scar is sometime visible. No observable paratabulation on the endocyst except in the vicinity of the endoarcheopyle.
The archeopyle is a combination archeopyle with the formula 3 (IP)@. Compound operculum with 1a, 2a and 3a separating laterally but remaining attached to the 3", 4" and 5" respectively. Accessory archeopyle sutures may be partially or completely developed between the precingular paraplates 2"-3", 3"-4", 4"-5" and 5"-6". The shape of the 2a plate is attenuated hexa to standard hexa. The 1a and 3a are very large. The endophragm and periphragm are appressed near the base of the intercalary paraplates. As a result the endoperculum is usually attached to the perioperculum. Rarely one or more intercalary paraplates from the endoperculum may be found within the endocoel. The archeopyle formula is: 3(IP)@ [(1a + 3")@ + (2a + 4")@ + (3a + 5")@].
A periopisthopyle (ventral antapical opening) may be formed between the antapical horns.
Size: Range of 37 specimens: pericyst length 60-85 µm, width at paracingulum 30-55 µm.
Holotype: Lentin, 1983, pl.1, figs.1a-b; Fensome et al., 1993a, figs.1-2 - p.963.
Locus typicus: Latitude 73¦26"5"N, longitude 123¦56"45"W, Banks Island, Northwest Territories, Canada
Stratum typicum: Maastrichtian
Original diagnosis: Lentin, 1983, p.148,150
Pericyst ambitus rhomboidal to subpentagonal, elongated in an anteroposterior direction. Pericyst prolonged into one apical and two symmetrically placed antapical horns, the right antapical generally reduced or vestigial. The pericyst attains its greatest width in the region of the pericingulum. Cyst dorsoventrally compressed.
Endocyst ambitus circular to ovoidal to rhomboidal in dorsoventral view. May be in contact with pericyst in precingular, cingular and postcingular regions as well as the base of the intercalary paraplates. Apical and antapical pericoels always present. The apical and antapical pericoels may be united by an ambital pericoel.
Thickness of the periphragm variable but usually ca. 1 µm. Surface generally laevigate, occasionally scabrate, granulate, or verrucate. The endophragm rarely exceeds 1 µm and is of constant thickness. Surface generally laevigate.
Paratabulation indeterminate except in the vicinity of the periarcheopyle which indicates a peridinioid style of tabulation. Paracingulum may or may not be well developed, planar or slightly helicoidal, with anterior parasuture only, or anterior and posterior parasuture as a slightly raised ridge or border, with smooth or denticulate margins. The parasulcus is rarely determinable; when visible largely restricted to the hypopericyst. A flagellar scar is sometime visible. No observable paratabulation on the endocyst except in the vicinity of the endoarcheopyle.
The archeopyle is a combination archeopyle with the formula 3 (IP)@. Compound operculum with 1a, 2a and 3a separating laterally but remaining attached to the 3", 4" and 5" respectively. Accessory archeopyle sutures may be partially or completely developed between the precingular paraplates 2"-3", 3"-4", 4"-5" and 5"-6". The shape of the 2a plate is attenuated hexa to standard hexa. The 1a and 3a are very large. The endophragm and periphragm are appressed near the base of the intercalary paraplates. As a result the endoperculum is usually attached to the perioperculum. Rarely one or more intercalary paraplates from the endoperculum may be found within the endocoel. The archeopyle formula is: 3(IP)@ [(1a + 3")@ + (2a + 4")@ + (3a + 5")@].
A periopisthopyle (ventral antapical opening) may be formed between the antapical horns.
Size: Range of 37 specimens: pericyst length 60-85 µm, width at paracingulum 30-55 µm.