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Meiourogonyaulax bulloidea
From Fensome et al., 2019:
Meiourogonyaulax bulloidea (Cookson and Eisenack, 1960b, p.247, pl.37, fig.11; text-figs.4a–b) Sarjeant, 1969, p.14. Emendation: Riding and Helby, 2001g, p.206, as Meiourogonyaulax bulloidea. Holotype: Cookson and Eisenack, 1960b, pl.37, fig.11. Originally Gonyaulax (Appendix B), subsequently (and now) Meiourogonyaulax, thirdly Lithodinia. This species is retained in Meiourogonyaulax following the retention of the genus by Riding and Helby (2001d, p.81,83). Backhouse (1988, p.95) considered Meiourogonyaulax stoveri to be the possible taxonomic senior synonym of this species. Age: Tithonian.
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Locus typicus: Canning Basin, Australia
Stratum typicum: Thitonian
Original description: Cookson and Eisenack, 1960, p.247: Gonyaulax bulloidea
Shell sphaerical, rather thick-walled, epitheca and hypotheca nearly equal, seperated by a rather broad, helicoidal girdle. Longitudinal furrow broadened towards the antapex. Plates mostly squarish or broadly trapezoid; plates 2' and 3' especially large, palte 1''' rather large, nearly rectangular. Formula 4', 6'', 6''', 1p, 1''''. The girdle, longitudinal furrow, and paltes are bordered by low but well-developed ledges; both plates and ledges are granular, a feature which, when taken in conjuntion with the sphaerical shape and squarish plates, gives the shell a very characteristic appearance. The apex is marked by a small pointed projection. In all the examples observed, plate 3'', which in many species of Gonyaulax becomes detached to form the pylome, has always been in position. On the other ahnd, in some specimens the apical plates have been missing (?Ekdysis).
Dimensions: Holotype 78 µm long, 83 µm broad. Range 60-88x57-83 µm.
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Emended description Riding and Helby, 2001g
Emended description. A species of Meiourogonyaulax, subspherical to ellipsoidal in shape; slightly dorsoventrally compressed and intermediate in size. Paratabulation fully indicated by low (2-3µm), narrow, distally smooth, microreticulate crests up to 5µm in height. The crests are occasionally irregularly fenestrate and are highest at gonal points and at the antapex. The crests coalesce at the apex to form a low,
distally rounded apical horn or protuberance, up to 5µm high. The paracingulum is equatorial and not subdivided. Similarly, the slightly indented parasulcus is also not subdivided. Autophragm thick ( 1.5 -3µm), smooth and microreticulate. Fenestrae are usually less than 0.5µm in diameter.
Dimensions (µm, n= 12) incl. crests, horns etc. where appropriate: Min. (Mean) Max.
Length of entire cyst: 75 (83) 90
Length of loisthocyst: 65 (73) 83
Width of cyst: 76 (83) 91
All specimens measured are topotypes from ditch cuttings in the Jarlemai Siltstone (Tithonian) of Broome-I Bore, Western Australia at 297.79m.
Comments. The thick, microreticulate autophragm is characteristic of this taxon. The subspherical shape and the broadly similar size and shape of the epicyst and hypocyst of M bulloidea mean that typically these cysts are equatorially and laterally symmetrical. The parasutural crests are distinctively smooth and microreticulate, and typically about 3μm high (Fig. 14F). However, crests are higher gonally and close to the antapex. In some specimens, the parasutural crests appear to be significantly reduced in height ventrally. This can make the paratabulation difficult to discern, and the orientation problematical.
This species is emended to record the characteristic microreticulate nature of the autophragm and parasutural crests. In the original description, the cyst wall and 'ledges' were described as '±granular' (Cookson & Eisenack, 1960, p. 247). The 12 topotype specimens studied are slightly larger than the type material of Cookson & Eisenack (1960). This emendation is based entirely on topotypes and does not take into account the wider morphological variation of this species noted in other material. Comparison. Meiourogonyaulax bulloidea is distinctive in being significantly larger than most other species of the genus. However, the relatively large M pertusa (Duxbury 1977) Below 1981 closely resembles M bulloidea in that it also has thick, perforate autophragm and low, distally smooth parasutural crests. Duxbury ( 1977, p. 42, fig. 42) showed that the paracingulum and parasulcus of M pertusa are subdivided. Parasutures within the paracingular and parasulcal areas of M bulloidea have not been observed. Furthermore, M pertusa is slightly smaller than M bulloidea and is more elongate. Meiourogonyaulax strongyla Sarjeant 1972, another large cyst, has denticulate parasutural crests and a granulate autophragm. The Bathonian M superornata (W. Wetzel I 967) Sarjeant I 969 is also large, but differs from M bulloidea in having very high parasutural crests. Meiourogonyaulax bulloidea also closely resembles M viriosa Riding & Helby (this volume) in shape and in having a microreticulate autophragm. However, the latter is normally smaller than M bulloidea and may have distally denticulate parasutural crests (see below). Moreover, the apical protuberance in M. viriosa is a solid boss-like feature; by contrast, the apical structure in M bulloidea is formed by the coalescence of parasutural crests. Backhouse (1988, p. 95) noted that the Early Cretaceous form Meiourogonyaulax stoveri Millioud 1969 may be a variant of M bulloidea. Meiourogonyaulax stoveri has distally smooth parasutural crests and a perforate/reticulate autophragm. The fenestrae in the autophragm of M stoveri are, however, much larger than those in M bulloidea. Also, the outline of Meiourogonyaulax stoveri is also much more elongate than that of M bulloidea and the former lacks an apical structure of any kind.
Holotype and type locality. The holotype is from ditch cuttings in the upper portion of Jarlemai Siltstone (Tithonian) in Broome-I Bore, Western Australia at 297.79m. It is in the Museum of Victoria, Melbourne as specimen number P. l 7788 (Cookson & Eisenack, 1960).
Stratigraphical distribution. Meiourogonyaulax bulloidea ranges from the Tithonian Cribroperidinium perforans Zone (5d) to the lowermost Valanginian Egmontodinium torynum Zone ( 4ai/4aii). It occurs consistently from the Tithonian upper Dingodinium jurassicum Zone (5ai) to the Berriasian Cassiculosphaeridia delicata Zone (4bii) (Foster, this volume; Helby & Partridge, in prep.).
Meiourogonyaulax bulloidea (Cookson and Eisenack, 1960b, p.247, pl.37, fig.11; text-figs.4a–b) Sarjeant, 1969, p.14. Emendation: Riding and Helby, 2001g, p.206, as Meiourogonyaulax bulloidea. Holotype: Cookson and Eisenack, 1960b, pl.37, fig.11. Originally Gonyaulax (Appendix B), subsequently (and now) Meiourogonyaulax, thirdly Lithodinia. This species is retained in Meiourogonyaulax following the retention of the genus by Riding and Helby (2001d, p.81,83). Backhouse (1988, p.95) considered Meiourogonyaulax stoveri to be the possible taxonomic senior synonym of this species. Age: Tithonian.
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Locus typicus: Canning Basin, Australia
Stratum typicum: Thitonian
Original description: Cookson and Eisenack, 1960, p.247: Gonyaulax bulloidea
Shell sphaerical, rather thick-walled, epitheca and hypotheca nearly equal, seperated by a rather broad, helicoidal girdle. Longitudinal furrow broadened towards the antapex. Plates mostly squarish or broadly trapezoid; plates 2' and 3' especially large, palte 1''' rather large, nearly rectangular. Formula 4', 6'', 6''', 1p, 1''''. The girdle, longitudinal furrow, and paltes are bordered by low but well-developed ledges; both plates and ledges are granular, a feature which, when taken in conjuntion with the sphaerical shape and squarish plates, gives the shell a very characteristic appearance. The apex is marked by a small pointed projection. In all the examples observed, plate 3'', which in many species of Gonyaulax becomes detached to form the pylome, has always been in position. On the other ahnd, in some specimens the apical plates have been missing (?Ekdysis).
Dimensions: Holotype 78 µm long, 83 µm broad. Range 60-88x57-83 µm.
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Emended description Riding and Helby, 2001g
Emended description. A species of Meiourogonyaulax, subspherical to ellipsoidal in shape; slightly dorsoventrally compressed and intermediate in size. Paratabulation fully indicated by low (2-3µm), narrow, distally smooth, microreticulate crests up to 5µm in height. The crests are occasionally irregularly fenestrate and are highest at gonal points and at the antapex. The crests coalesce at the apex to form a low,
distally rounded apical horn or protuberance, up to 5µm high. The paracingulum is equatorial and not subdivided. Similarly, the slightly indented parasulcus is also not subdivided. Autophragm thick ( 1.5 -3µm), smooth and microreticulate. Fenestrae are usually less than 0.5µm in diameter.
Dimensions (µm, n= 12) incl. crests, horns etc. where appropriate: Min. (Mean) Max.
Length of entire cyst: 75 (83) 90
Length of loisthocyst: 65 (73) 83
Width of cyst: 76 (83) 91
All specimens measured are topotypes from ditch cuttings in the Jarlemai Siltstone (Tithonian) of Broome-I Bore, Western Australia at 297.79m.
Comments. The thick, microreticulate autophragm is characteristic of this taxon. The subspherical shape and the broadly similar size and shape of the epicyst and hypocyst of M bulloidea mean that typically these cysts are equatorially and laterally symmetrical. The parasutural crests are distinctively smooth and microreticulate, and typically about 3μm high (Fig. 14F). However, crests are higher gonally and close to the antapex. In some specimens, the parasutural crests appear to be significantly reduced in height ventrally. This can make the paratabulation difficult to discern, and the orientation problematical.
This species is emended to record the characteristic microreticulate nature of the autophragm and parasutural crests. In the original description, the cyst wall and 'ledges' were described as '±granular' (Cookson & Eisenack, 1960, p. 247). The 12 topotype specimens studied are slightly larger than the type material of Cookson & Eisenack (1960). This emendation is based entirely on topotypes and does not take into account the wider morphological variation of this species noted in other material. Comparison. Meiourogonyaulax bulloidea is distinctive in being significantly larger than most other species of the genus. However, the relatively large M pertusa (Duxbury 1977) Below 1981 closely resembles M bulloidea in that it also has thick, perforate autophragm and low, distally smooth parasutural crests. Duxbury ( 1977, p. 42, fig. 42) showed that the paracingulum and parasulcus of M pertusa are subdivided. Parasutures within the paracingular and parasulcal areas of M bulloidea have not been observed. Furthermore, M pertusa is slightly smaller than M bulloidea and is more elongate. Meiourogonyaulax strongyla Sarjeant 1972, another large cyst, has denticulate parasutural crests and a granulate autophragm. The Bathonian M superornata (W. Wetzel I 967) Sarjeant I 969 is also large, but differs from M bulloidea in having very high parasutural crests. Meiourogonyaulax bulloidea also closely resembles M viriosa Riding & Helby (this volume) in shape and in having a microreticulate autophragm. However, the latter is normally smaller than M bulloidea and may have distally denticulate parasutural crests (see below). Moreover, the apical protuberance in M. viriosa is a solid boss-like feature; by contrast, the apical structure in M bulloidea is formed by the coalescence of parasutural crests. Backhouse (1988, p. 95) noted that the Early Cretaceous form Meiourogonyaulax stoveri Millioud 1969 may be a variant of M bulloidea. Meiourogonyaulax stoveri has distally smooth parasutural crests and a perforate/reticulate autophragm. The fenestrae in the autophragm of M stoveri are, however, much larger than those in M bulloidea. Also, the outline of Meiourogonyaulax stoveri is also much more elongate than that of M bulloidea and the former lacks an apical structure of any kind.
Holotype and type locality. The holotype is from ditch cuttings in the upper portion of Jarlemai Siltstone (Tithonian) in Broome-I Bore, Western Australia at 297.79m. It is in the Museum of Victoria, Melbourne as specimen number P. l 7788 (Cookson & Eisenack, 1960).
Stratigraphical distribution. Meiourogonyaulax bulloidea ranges from the Tithonian Cribroperidinium perforans Zone (5d) to the lowermost Valanginian Egmontodinium torynum Zone ( 4ai/4aii). It occurs consistently from the Tithonian upper Dingodinium jurassicum Zone (5ai) to the Berriasian Cassiculosphaeridia delicata Zone (4bii) (Foster, this volume; Helby & Partridge, in prep.).