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Spinidinium tripylum
Spinidinium ?tripylum Kurita, 2004, p.42, pl.2, figs.1–13; text-fig.10b.
Holotype: Kurita, 2004, pl.2, figs.1–4,13.
Questionable assignment: Kurita (2004, p.42).
Age: late Oligocene.
Original description (Kurita, 2004)
Holotype: Sample KR903-005, slide Dn-1, 95.6x22.7 (text-figure 10b; Plate 2, figs. 1-4, 13)
Paratypes: Sample KR903-005, slide Dn-1, 95.0x11.8 (Plate 2, Fig. 5) Sample KR903-012, slide Dn-2, 94.0x4.5 (Plate 2, figs. 7-9)
Repository: Stored in the palynological collection at the Department of Geology, Faculty of Science, Niigata University.
Type locality: KR903-005, Honbetsu-zawa tributary, Honbetsu Town, Tokachi Province, Hokkaido, Japan; latitude 43º09'50"N, longitude 143º41'52"E.
Type stratum: Honbetsuzawa Formation (Mitani et al. 1959), Upper? Oligocene (Kurita et al. 1998b).
Derivation of name: tri-, Latin, three; pylus, Latin, opening, referring to the compound archeopyle that involves three intercalary paraplates.
Diagnosis: A species provisionally assigned to the genus Spinidinium with pericyst peridinioid to ovoidal and with one apical and two antapical horns. Cyst cornucavate, occasionally bicavate or epicavate. Archeopyle compound, (IP)@+ (IP)@+ (IP)@ (text-fig. 10b).
Description: Pericyst peridinioid to ovoidal with one apical and two antapical horns; cornucavate, occasionally bicavate or epicavate. On pericyst, short spines which are usually simple solid ornaments, or rarely triangular, flap-like, somewhat membranous projection. Spines arranged generally in penitabular rows. Density of spines variable. Apical pericoel always relatively large, resulting from inflation of pericyst in epicyst (shoulders). Paracingulum indicated by two parallel rows of spines or by two parallel ridges with spines on them, about
2.5µm apart. Parasulcus indicated by lack of paracingular rows or ridges and shallow depression of the cyst in the ventral area. Endocyst ovoidal to circular. Both pericyst and endocyst pale, transparent and smooth. Paratabulation indicated by the penitabular arrangement of the spines, paracingular rows or ridges, parasulcus and archeopyle. Archeopyle compound, (IP)@+ (IP)@+ (IP)@ (text-fig. 10a).
Dimensions: Overall cyst length 57-65µm; width 45-57µm. Spine length up to 1.2µm. Apical horn length 7µm; larger antapical horn length up to 5µm.
Occurrence: Rare to abundant in the Honbetsuzawa and Nisho Formations and the lower part of the Kiroro Formation, Kawakami Group, Shiranuka area; Operculodinium sp. A Zone to Spinidinium? tripylum sp. nov. Zone, which are Upper Oligocene and questionable Upper Oligocene. Observed range in this study: Upper Oligocene, including sections questionably assigned to it.
Remarks: Spinidinium? tripylum sp. nov. is characterized by its peridinioid to ovoidal shape, short spines which are arranged in penitabular rows and the compound archeopyle. The penitabular arrangement of the spines is often typically observed in the apical and intercalary paraplates. A relatively large apical pericoel is also characteristics of the species. The archeopyle is indicated by slits frequently observed between the precingular paraplates right beneath the intercalary paraplates (text-fig. 10b). The archeopyle of Spinidinium? tripylum sp. nov. does not allow direct assignment to the genus Spinidinium, which has a simple 2a intercalary archeopyle; rather it could be included in Williamsidinium. Other genera whose archeopyle involves three anterior intercalary paraplates include Ginginodinium, Pierceites, Ripea, Trithyrodinium and Trivalvadinium. Spinidinium? tripylum sp. nov. is not comparable to those genera in view of wall relationship and cyst overall shape etc. Presently the species is provisionally assigned to Spinidinium, because of the well discernible penitabular spines which are characteristic to Spinidinium and have never been reported on Williamsidinium species.
Holotype: Kurita, 2004, pl.2, figs.1–4,13.
Questionable assignment: Kurita (2004, p.42).
Age: late Oligocene.
Original description (Kurita, 2004)
Holotype: Sample KR903-005, slide Dn-1, 95.6x22.7 (text-figure 10b; Plate 2, figs. 1-4, 13)
Paratypes: Sample KR903-005, slide Dn-1, 95.0x11.8 (Plate 2, Fig. 5) Sample KR903-012, slide Dn-2, 94.0x4.5 (Plate 2, figs. 7-9)
Repository: Stored in the palynological collection at the Department of Geology, Faculty of Science, Niigata University.
Type locality: KR903-005, Honbetsu-zawa tributary, Honbetsu Town, Tokachi Province, Hokkaido, Japan; latitude 43º09'50"N, longitude 143º41'52"E.
Type stratum: Honbetsuzawa Formation (Mitani et al. 1959), Upper? Oligocene (Kurita et al. 1998b).
Derivation of name: tri-, Latin, three; pylus, Latin, opening, referring to the compound archeopyle that involves three intercalary paraplates.
Diagnosis: A species provisionally assigned to the genus Spinidinium with pericyst peridinioid to ovoidal and with one apical and two antapical horns. Cyst cornucavate, occasionally bicavate or epicavate. Archeopyle compound, (IP)@+ (IP)@+ (IP)@ (text-fig. 10b).
Description: Pericyst peridinioid to ovoidal with one apical and two antapical horns; cornucavate, occasionally bicavate or epicavate. On pericyst, short spines which are usually simple solid ornaments, or rarely triangular, flap-like, somewhat membranous projection. Spines arranged generally in penitabular rows. Density of spines variable. Apical pericoel always relatively large, resulting from inflation of pericyst in epicyst (shoulders). Paracingulum indicated by two parallel rows of spines or by two parallel ridges with spines on them, about
2.5µm apart. Parasulcus indicated by lack of paracingular rows or ridges and shallow depression of the cyst in the ventral area. Endocyst ovoidal to circular. Both pericyst and endocyst pale, transparent and smooth. Paratabulation indicated by the penitabular arrangement of the spines, paracingular rows or ridges, parasulcus and archeopyle. Archeopyle compound, (IP)@+ (IP)@+ (IP)@ (text-fig. 10a).
Dimensions: Overall cyst length 57-65µm; width 45-57µm. Spine length up to 1.2µm. Apical horn length 7µm; larger antapical horn length up to 5µm.
Occurrence: Rare to abundant in the Honbetsuzawa and Nisho Formations and the lower part of the Kiroro Formation, Kawakami Group, Shiranuka area; Operculodinium sp. A Zone to Spinidinium? tripylum sp. nov. Zone, which are Upper Oligocene and questionable Upper Oligocene. Observed range in this study: Upper Oligocene, including sections questionably assigned to it.
Remarks: Spinidinium? tripylum sp. nov. is characterized by its peridinioid to ovoidal shape, short spines which are arranged in penitabular rows and the compound archeopyle. The penitabular arrangement of the spines is often typically observed in the apical and intercalary paraplates. A relatively large apical pericoel is also characteristics of the species. The archeopyle is indicated by slits frequently observed between the precingular paraplates right beneath the intercalary paraplates (text-fig. 10b). The archeopyle of Spinidinium? tripylum sp. nov. does not allow direct assignment to the genus Spinidinium, which has a simple 2a intercalary archeopyle; rather it could be included in Williamsidinium. Other genera whose archeopyle involves three anterior intercalary paraplates include Ginginodinium, Pierceites, Ripea, Trithyrodinium and Trivalvadinium. Spinidinium? tripylum sp. nov. is not comparable to those genera in view of wall relationship and cyst overall shape etc. Presently the species is provisionally assigned to Spinidinium, because of the well discernible penitabular spines which are characteristic to Spinidinium and have never been reported on Williamsidinium species.