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Striatodinium ottii
Striatodinium *ottii Riding and Helby, 2001f, p.170–171, figs.15A–P. Holotype: Riding and Helby, 2001f, figs.15O–P. Taxonomic junior synonym: Dictyopyxis elliptica (name not validly published), according to Riding and Helby (2001f, p.170). Age: Oxfordian–earliest Kimmeridgian.
Original description (Riding and Helby, 2001f)
Description. A species of Striatodinium which is dorsoventrally flattened and having a smooth to microscabrate autophragm which is 1 µm thick. Slender (<0.5µm thick), straight, distally smooth periphragmal crests emerge from penitabular positions on each major paraplate. The penitabular ridges on paracingular and possibly the parasulcal plates tend to be discontinuous. The crests are prominent (2-4 µm high), tend to be slightly higher in the antapical region and appear to be predominantly longitudinal due to the elongate nature of the species. The paracingulum is relatively narrow.
Dimensions (µm; n=41) exclusive of penitabular crests where applicable: Min. (Mean) Max.
Length of loisthocyst: 45 (56) 68
Length of precingular paraplate series*: 18 (25) 31
Length of paracingulum*: 3 (4.5) 6
Length of postcingular paraplate series*: 20 (26) 30
Equatorial width of cyst: 20 (28) 34
Height of penitabular crests: 2 (3) 4
*-measured in dorsal view
Only one cyst with an adherent operculum was observed; it was 53 µm in overall length and the operculum was 7 µm long. The measured specimens are from a ditch cuttings sample from Peak-1 well between 1493.54m and 1496.59m and outcrop material from the uppermost Ohineruru Formation (Kimmeridgian) from Kawhia, New Zealand (sample f8556 of Helby et al., 1988).
Comments: The penitabular crests of Striatodinium ottii are predominantly longitudinal because of the elongate nature of this species; the polar sides of each of the precingular and postcingular paraplates are short. This species generally appears symmetrical, particularly in dorsal view, because the epicyst and hypocyst are similar in size. The penitabular crests are normally developed. The penitabular crests emerge from immediately (within 1-2µm) inside each paraplate area. These crests are interpreted as being formed entirely of periphragmal extensions; no cavation has been observed. No degradation of the penitabular crests was observed. As in S. lineatum, the overwhelming majority of the specimens studied are loisthocysts.
Comparison: Striatodinium ottii is larger than S. lineatum; it also differs in having penitabular crests and lacking nontabular ornamentation.
Derivation of name. For Hank L. Ott.
Holotype and type locality: From sample f8556 of Helby et al., (1988), collected in the uppermost Ohineruru Formation (Kimmeridgian) from Kawhia, New Zealand. The holotype and the topotypes are curated in the collections of the Institute of Geological and Nuclear Sciences (formerly the New Zealand Geological Survey), Lower Hutt, New Zealand.
Stratigraphical distribution: Striatodiniumn ottii ranges from th eOxfordian-Kimmeridgian upper part of the Wanaea clathrata Zone (6bi) to the basal part of the Kimmeridgian Dingodinium swanense Zone (6aiiib). It occurs consistently over this interval in the Carnarvon Basin, Western Australia but is extremely rare to the north in the Timor Sea region. It has not been recorded in the Misool. The species is also present in the Kimmeridgian uppermost Ohineruru Formation of Kawhia, New Zealamd (Helby et al., 1988).
Original description (Riding and Helby, 2001f)
Description. A species of Striatodinium which is dorsoventrally flattened and having a smooth to microscabrate autophragm which is 1 µm thick. Slender (<0.5µm thick), straight, distally smooth periphragmal crests emerge from penitabular positions on each major paraplate. The penitabular ridges on paracingular and possibly the parasulcal plates tend to be discontinuous. The crests are prominent (2-4 µm high), tend to be slightly higher in the antapical region and appear to be predominantly longitudinal due to the elongate nature of the species. The paracingulum is relatively narrow.
Dimensions (µm; n=41) exclusive of penitabular crests where applicable: Min. (Mean) Max.
Length of loisthocyst: 45 (56) 68
Length of precingular paraplate series*: 18 (25) 31
Length of paracingulum*: 3 (4.5) 6
Length of postcingular paraplate series*: 20 (26) 30
Equatorial width of cyst: 20 (28) 34
Height of penitabular crests: 2 (3) 4
*-measured in dorsal view
Only one cyst with an adherent operculum was observed; it was 53 µm in overall length and the operculum was 7 µm long. The measured specimens are from a ditch cuttings sample from Peak-1 well between 1493.54m and 1496.59m and outcrop material from the uppermost Ohineruru Formation (Kimmeridgian) from Kawhia, New Zealand (sample f8556 of Helby et al., 1988).
Comments: The penitabular crests of Striatodinium ottii are predominantly longitudinal because of the elongate nature of this species; the polar sides of each of the precingular and postcingular paraplates are short. This species generally appears symmetrical, particularly in dorsal view, because the epicyst and hypocyst are similar in size. The penitabular crests are normally developed. The penitabular crests emerge from immediately (within 1-2µm) inside each paraplate area. These crests are interpreted as being formed entirely of periphragmal extensions; no cavation has been observed. No degradation of the penitabular crests was observed. As in S. lineatum, the overwhelming majority of the specimens studied are loisthocysts.
Comparison: Striatodinium ottii is larger than S. lineatum; it also differs in having penitabular crests and lacking nontabular ornamentation.
Derivation of name. For Hank L. Ott.
Holotype and type locality: From sample f8556 of Helby et al., (1988), collected in the uppermost Ohineruru Formation (Kimmeridgian) from Kawhia, New Zealand. The holotype and the topotypes are curated in the collections of the Institute of Geological and Nuclear Sciences (formerly the New Zealand Geological Survey), Lower Hutt, New Zealand.
Stratigraphical distribution: Striatodiniumn ottii ranges from th eOxfordian-Kimmeridgian upper part of the Wanaea clathrata Zone (6bi) to the basal part of the Kimmeridgian Dingodinium swanense Zone (6aiiib). It occurs consistently over this interval in the Carnarvon Basin, Western Australia but is extremely rare to the north in the Timor Sea region. It has not been recorded in the Misool. The species is also present in the Kimmeridgian uppermost Ohineruru Formation of Kawhia, New Zealamd (Helby et al., 1988).