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Meiourogonyaulax straussii
Meiourogonyaulax straussii Mantle and Riding, 2012, p.57–58,61, pl.1, figs.1–16.
Holotype: Mantle and Riding, 2012, pl.1, figs.5–6.
Age: late Bajocian–early Bathonian.
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Original description (Mantle & Riding, 2012)
Meiourogonyaulax straussii sp. nov. (Plate I, 1–16)
Description: A species of Meiourogonyaulax which is ellipsoidal in dorsoventral outline; an apical horn or protuberance is entirely lacking. The autophragm is robust, thick, comprehensively rugulate to irregularly reticulate and locally may bear elements of low-relief ornamentation such as baculae, denticles/echinae, tubercles, and verrucae. The density and type of this ornament is highly variable, ranging from largely spinose forms to comprehensively rugulate morphotypes. Locally, the coalescence of verrucae and rugulae gives rise to a pseudoreticulate texture. The spinose-baculate elements are typically irregularly distributed and are highly variable in form, for example they may be either distally blunt, sharp or oblate. These elements are consistently most well-developed on the hypocyst, and especially around the antapical (1””) plate, although some specimens are comprehensively spinose. The sexiform gonyaulacacean tabulation is indicated by the apical archaeopyle, the prominent crests which consistently mark the apparently undivided laevorotatory cingulum, and by low, frequently discontinuous sutural ridges or crests which delineate the remaining plate series. The tabulation is largely suppressed in the apical and antapical areas. Frequently, the crests/ridges in the precingular and postcingular plate series become lower and more discontinuous in a polar direction either side of the cingulum, becoming entirely suppressed towards the middle point of these series. The sutural crests/ridges, where developed, dominantly have irregular distal margins formed by denticles, but they can occasionally be distally smooth or fenestrate. Relatively large, dark accumulation bodies which are subspherical to ovoidal in outline are centrally attached to the cyst body on most specimens. The sulcus is apparently undivided, relatively narrow and longitudinal. The archaeopyle is apical; the simple operculum is nearly always attached. Minor accessory archaeopyle sutures may be developed in the precingular plate series.
Dimensions (30 specimens measured):
Length of cyst including operculum: 45 (60) 75 μm
Equatorial width of cyst: 58 (69) 82 μm
Height of ornamentation: 0.5–4.0 μm
Thickness of autophragm: 1–1.5 μm
Comments: Meiourogonyaulax straussii sp. nov. is easily recognised by its thick and robust, rugulate to irregularly reticulate autophragm, the prominent cingulum, its partially-developed sutural crests/ridges, the variable low-relief ornamentation which is best developed around the antapex, the frequently attached simple apical operculum and the prominent accumulation bodies. The morphology of the sutural crests/ridges is highly variable, they typically have irregularly denticulate distal margins, but these can also be distally smooth or fenestrate. This species is prominent, even when working at relatively low magnifications due to its thick autophragm, which imparts a strong body colour.
Comparison: Meiourogonyaulax straussii sp. nov. differs from all other species of Meiourogonyaulax in bearing significantly incomplete tabulation. Stover and Evitt (1978, p. 62) stated that the tabulation is ‘generally complete’. The species which is most similar is Meiourogonyaulax reticulata Dodekova 1975, which has a thick, reticulate autophragm and a frequently attached operculum. However, the tabulation of Meiourogonyaulax reticulata is fully indicated by low, distally-smooth sutural ridges (Riding, 1983, pl. 1).
Holotype and type locality: Plate I, 5–6. Sunset West-1 well (2216.84 m), Bonaparte Basin, Timor Sea. Slide no. 2, EF T39/2, CPC no. 41142.
Stratigraphical distribution: Meiourogonyaulax straussii sp. nov. was observed commonly in the Wanaea verrucosa Zone in both the Sunrise-2 and Sunset West-1 wells. It first appears in the middle part of the Lower Subzone, is common to abundant in the upper half of the Middle Subzone to the lower part of the Upper Subzone and ranges sporadically into the overlying Wanaea indotata Zone (Tables 2 and 3). Meiourogonyaulax straussii was also recorded in low to moderate numbers in the Wanaea verrucosa Zone of the Perseus-3A well (Table 1).
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Holotype: Mantle and Riding, 2012, pl.1, figs.5–6.
Age: late Bajocian–early Bathonian.
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Original description (Mantle & Riding, 2012)
Meiourogonyaulax straussii sp. nov. (Plate I, 1–16)
Description: A species of Meiourogonyaulax which is ellipsoidal in dorsoventral outline; an apical horn or protuberance is entirely lacking. The autophragm is robust, thick, comprehensively rugulate to irregularly reticulate and locally may bear elements of low-relief ornamentation such as baculae, denticles/echinae, tubercles, and verrucae. The density and type of this ornament is highly variable, ranging from largely spinose forms to comprehensively rugulate morphotypes. Locally, the coalescence of verrucae and rugulae gives rise to a pseudoreticulate texture. The spinose-baculate elements are typically irregularly distributed and are highly variable in form, for example they may be either distally blunt, sharp or oblate. These elements are consistently most well-developed on the hypocyst, and especially around the antapical (1””) plate, although some specimens are comprehensively spinose. The sexiform gonyaulacacean tabulation is indicated by the apical archaeopyle, the prominent crests which consistently mark the apparently undivided laevorotatory cingulum, and by low, frequently discontinuous sutural ridges or crests which delineate the remaining plate series. The tabulation is largely suppressed in the apical and antapical areas. Frequently, the crests/ridges in the precingular and postcingular plate series become lower and more discontinuous in a polar direction either side of the cingulum, becoming entirely suppressed towards the middle point of these series. The sutural crests/ridges, where developed, dominantly have irregular distal margins formed by denticles, but they can occasionally be distally smooth or fenestrate. Relatively large, dark accumulation bodies which are subspherical to ovoidal in outline are centrally attached to the cyst body on most specimens. The sulcus is apparently undivided, relatively narrow and longitudinal. The archaeopyle is apical; the simple operculum is nearly always attached. Minor accessory archaeopyle sutures may be developed in the precingular plate series.
Dimensions (30 specimens measured):
Length of cyst including operculum: 45 (60) 75 μm
Equatorial width of cyst: 58 (69) 82 μm
Height of ornamentation: 0.5–4.0 μm
Thickness of autophragm: 1–1.5 μm
Comments: Meiourogonyaulax straussii sp. nov. is easily recognised by its thick and robust, rugulate to irregularly reticulate autophragm, the prominent cingulum, its partially-developed sutural crests/ridges, the variable low-relief ornamentation which is best developed around the antapex, the frequently attached simple apical operculum and the prominent accumulation bodies. The morphology of the sutural crests/ridges is highly variable, they typically have irregularly denticulate distal margins, but these can also be distally smooth or fenestrate. This species is prominent, even when working at relatively low magnifications due to its thick autophragm, which imparts a strong body colour.
Comparison: Meiourogonyaulax straussii sp. nov. differs from all other species of Meiourogonyaulax in bearing significantly incomplete tabulation. Stover and Evitt (1978, p. 62) stated that the tabulation is ‘generally complete’. The species which is most similar is Meiourogonyaulax reticulata Dodekova 1975, which has a thick, reticulate autophragm and a frequently attached operculum. However, the tabulation of Meiourogonyaulax reticulata is fully indicated by low, distally-smooth sutural ridges (Riding, 1983, pl. 1).
Holotype and type locality: Plate I, 5–6. Sunset West-1 well (2216.84 m), Bonaparte Basin, Timor Sea. Slide no. 2, EF T39/2, CPC no. 41142.
Stratigraphical distribution: Meiourogonyaulax straussii sp. nov. was observed commonly in the Wanaea verrucosa Zone in both the Sunrise-2 and Sunset West-1 wells. It first appears in the middle part of the Lower Subzone, is common to abundant in the upper half of the Middle Subzone to the lower part of the Upper Subzone and ranges sporadically into the overlying Wanaea indotata Zone (Tables 2 and 3). Meiourogonyaulax straussii was also recorded in low to moderate numbers in the Wanaea verrucosa Zone of the Perseus-3A well (Table 1).
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