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Williamsidinium diaphanes
Williamsidinium diaphanes Kurita, 2004, p.43–44, pl.3, figs.1–9; text-fig.10a.
Holotype: Kurita, 2004, pl.3, figs.1–3; text-fig.10a.
Age: late Oligocene.
Original description (Kurita, 2004)
Holotype: Sample KR903-020, slide Dn-1, 109.1x17.6 (text-fig. 10a; Plate 3, figs. 1-3)
Paratype: Sample KR903-010, slide Dn-1, 96.0x12.8 (Plate 3, figs. 4-6)
Repository: Stored in the palynological collection at the Department of Geology, Faculty of Science, Niigata University Type locality: KR903-020, Honbetsu-zawa tributary, Honbetsu Town, Tokachi Province, Hokkaido, Japan; latitude 43o09’01"N, longitude 143o40’35"E. Type stratum: Lower part of the Kiroro Formation (Mitani et al. 1959), Upper Oligocene (Kurita et al. 1998b).
Derivation of name: diaphanes, Greek, transparent, referring to the thin, transparent cyst wall.
Diagnosis: A species of the genus Williamsidinium with cornucavate, occasionally bicavate or epicavate cyst which is relatively small and has a narrow shape. Apical pericoel large, while antapical pericoel relatively small. Epicyst larger than hypocyst. Archeopyle compound, Type (IP)@+ (IP)@+ (IP)@ (text-fig. 10a).
Description: Cyst cornucavate, occasionally bicavate or epicavate. Body shape varying from peridinioid to ovoidal, depending on the development of antapical horns. Epicyst larger than hypocyst. An apical horn always distinctive. Apical pericoel large. Two antapical horns, unequally developed, small or missing. Surface of pericyst rarely with sparse small grana. Paracingulum indicated by two parallel low crests in the equatorial area, which are ca. 3 µm apart; sometimes decorated by minute dentation on the crests. Parasulcus indicated by lack of paracingular crests and shallow, longitudinal depression of cyst. Endocyst circular to ellipsoidal; when ellipsoidal, width larger than length. Both pericyst and endocyst pale, transparent and smooth. Archeopyle compound, derived from partial detachment of three apical intercalary paraplates as well as three precingular paraplates adjoining right beneath the intercalary paraplates (text-fig. 10a), with archeopyle formula (IP)@+ (IP)@+ (IP)@. Operculum always adnate posteriorly.
Dimensions: Overall cyst length 63-75 µm; width 40-62 µm. Apical horn length 7-8 µm; larger antapical horn length up to 7 µm.
Occurrence: Rare to common in the Honbetsu-zawa and Nisho Formations and in the lower part of the Kiroro Formation, Kawakami Group, Shiranuka area; Williamsidinium diaphanes Zone to Spinidinium? tripylum Zone, which are Upper Oligocene and questionable Upper Oligocene. Folded specimens probably identical with the present species also abundant in the same interval (recorded as Williamsidinium diaphanes sp. nov. (probable)).Observed range in this study: Upper Oligocene, including sections questionably assigned to it.
Remarks: This species is distinctive in having ovoidal to peridinioid cyst ambital shape and (IP)@+ (IP)@+ (IP)@ type archeopyle which is typical for the genus (text-fig. 10a; Plate 3, figures 1-9). The cyst wall of this species is thin and folded easily. Numerous pale, double-walled peridinioid cysts from the same interval and in which the archeopyle is not discernible, are probably assignable to Williamsidinium diaphanes sp. nov.
Williamsidinium diaphanes sp. nov. differs from W. banksianum Lentin 1983, the type of the genus from the Upper Cretaceous, in being smaller and having a narrower body and smaller antapical pericoel. Williamsidinium? sp. from the Paleocene of the Western Interior of North America (Kurita and McIntyre 1994) is much larger than W. diaphanes sp. nov. and of different shape.Williamsidinium diaphanes sp. nov. occurs also in the Paleogene of Sakhalin, Far East Russia, where it was recorded as Williamsidinium sp. A by Kurita et al. (2000).
Holotype: Kurita, 2004, pl.3, figs.1–3; text-fig.10a.
Age: late Oligocene.
Original description (Kurita, 2004)
Holotype: Sample KR903-020, slide Dn-1, 109.1x17.6 (text-fig. 10a; Plate 3, figs. 1-3)
Paratype: Sample KR903-010, slide Dn-1, 96.0x12.8 (Plate 3, figs. 4-6)
Repository: Stored in the palynological collection at the Department of Geology, Faculty of Science, Niigata University Type locality: KR903-020, Honbetsu-zawa tributary, Honbetsu Town, Tokachi Province, Hokkaido, Japan; latitude 43o09’01"N, longitude 143o40’35"E. Type stratum: Lower part of the Kiroro Formation (Mitani et al. 1959), Upper Oligocene (Kurita et al. 1998b).
Derivation of name: diaphanes, Greek, transparent, referring to the thin, transparent cyst wall.
Diagnosis: A species of the genus Williamsidinium with cornucavate, occasionally bicavate or epicavate cyst which is relatively small and has a narrow shape. Apical pericoel large, while antapical pericoel relatively small. Epicyst larger than hypocyst. Archeopyle compound, Type (IP)@+ (IP)@+ (IP)@ (text-fig. 10a).
Description: Cyst cornucavate, occasionally bicavate or epicavate. Body shape varying from peridinioid to ovoidal, depending on the development of antapical horns. Epicyst larger than hypocyst. An apical horn always distinctive. Apical pericoel large. Two antapical horns, unequally developed, small or missing. Surface of pericyst rarely with sparse small grana. Paracingulum indicated by two parallel low crests in the equatorial area, which are ca. 3 µm apart; sometimes decorated by minute dentation on the crests. Parasulcus indicated by lack of paracingular crests and shallow, longitudinal depression of cyst. Endocyst circular to ellipsoidal; when ellipsoidal, width larger than length. Both pericyst and endocyst pale, transparent and smooth. Archeopyle compound, derived from partial detachment of three apical intercalary paraplates as well as three precingular paraplates adjoining right beneath the intercalary paraplates (text-fig. 10a), with archeopyle formula (IP)@+ (IP)@+ (IP)@. Operculum always adnate posteriorly.
Dimensions: Overall cyst length 63-75 µm; width 40-62 µm. Apical horn length 7-8 µm; larger antapical horn length up to 7 µm.
Occurrence: Rare to common in the Honbetsu-zawa and Nisho Formations and in the lower part of the Kiroro Formation, Kawakami Group, Shiranuka area; Williamsidinium diaphanes Zone to Spinidinium? tripylum Zone, which are Upper Oligocene and questionable Upper Oligocene. Folded specimens probably identical with the present species also abundant in the same interval (recorded as Williamsidinium diaphanes sp. nov. (probable)).Observed range in this study: Upper Oligocene, including sections questionably assigned to it.
Remarks: This species is distinctive in having ovoidal to peridinioid cyst ambital shape and (IP)@+ (IP)@+ (IP)@ type archeopyle which is typical for the genus (text-fig. 10a; Plate 3, figures 1-9). The cyst wall of this species is thin and folded easily. Numerous pale, double-walled peridinioid cysts from the same interval and in which the archeopyle is not discernible, are probably assignable to Williamsidinium diaphanes sp. nov.
Williamsidinium diaphanes sp. nov. differs from W. banksianum Lentin 1983, the type of the genus from the Upper Cretaceous, in being smaller and having a narrower body and smaller antapical pericoel. Williamsidinium? sp. from the Paleocene of the Western Interior of North America (Kurita and McIntyre 1994) is much larger than W. diaphanes sp. nov. and of different shape.Williamsidinium diaphanes sp. nov. occurs also in the Paleogene of Sakhalin, Far East Russia, where it was recorded as Williamsidinium sp. A by Kurita et al. (2000).