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Emmetrocysta cheleusis
Emmetrocysta cheleusis Stevens and Helby in Riding and Helby, 2001g, p.184.
Name not validly published: no description.
Taxonomic senior synonym: Balcattia cheleusis, according to Riding and Helby (2001g, p. 184).
(Riding and Helby, 2001g)
1994 Rigaudella sp. B ; Bint & Marshall, fig. 5.15.
Previous Australian usage
Emmetrocysta cheleusis Stevens & Helby (manuscript name)
Rigaudella separata – Parker (1986, p. 99-100, fig. 5.41, pl. 21, figs. 3-6)
Rigeuldella searata – Helby. MP 346 – Helby
Description: A species of Balcattia with a large, elongate ovoidal to subquadrangular cyst body. A small antapical protuberance may be present and the paracingular are is occasionally indented. The autophragm is moderately thin (0.5-1 µm), smooth to occasionally shagreenate or irregularly microscabrate. Intratabular processes, which are variable in morphology, are present on the precingular, postcingular, posterior intercalary and antapical paraplates. The hypocyst generally bears 7 processes and the epicyst has 5-6 processes . Processes are entirely absent in the paracingular area and the precingular and postcingular processes are inserted high and low respectively. This factor highlight the process-free equatorial region. The processes are variable in length, slender to wide (3-12 µm), mostly hollow, although some may be solid and other vacuolated. They are always distally expanded. At around midlength each process subdivides distally into slender, solid elements, which generally connect to the other processes and form a trabeculate ectophragmal layer. This expansion normally involves complex branching of the processes into fenestrate funnels. The processes may be interconnected by 1 to 5 slender trabeculate emanating from the distal parts of the processes. Alternatively, the distal part of the processes forms a complex, sheet-like fenestra ectophragm, which extents and connects to other processes. There are no trabeculate connections between the epicyst and hypocyst. All the specimens studied were loisthocysts and no free opercula were recognized.
Dimensions: (µm, n=26): Min.(Mean)Max.
Length of cyst incl. processes: 105(141)170
Length of cyst body (excl. processes): 56(69)94
Width of cyst incl. processes: 73(104)135
Width of cyst excl. processes: 37(54)78
Length of processes: 27(45)66
The measured specimens are from a convertional core sample from Mutineer-1B well at 3147.60m, sidewall core samples from Nancar-1 well at 3240.0m, Puratte-1 well at 172.0m, Scafell-1 well at 1421.0m and Wanaea-3 well at 2964.0m and ditch cuttings from Broome-1 Bore at 297.79m and Mindil-1 well between 3150.0m and 3155.0m
Comments: the distinctive species of Balcattia is large, and the size range is considerable. The processes haeve bipolar distribution and are positioned high on the precingular paraplate series and low on the postcingular paraplate series. All of the specimens studies were loisthocysts, and these were oriented by the position of the Archeopyle and the occasional presence of a small antapical protuberance. Where present, this protuberance bears the 1’’’’ processes. The processes are somewhat variable in morphology. Most are relatively long and slender; however, short and wide processes, although rare, were also observed. Only especially slender processes (1-2 µm in width) are solid, all other being hollow. On some specimens the precingular processes may be significantly shorted and those near the antapex. The specimens examined from the Broome-1 Bore do not exhibit distal trabeculation. This speices was originally informally assigned to Emmetrocysta Stover 1975 by Stevens & Helby (unpublished). However, that genus is characterized by paraplate-centered process complexes which are not joined by trabeculate strands and it is substantially smaller and consistently subspherical (Stover, 1975). Despite the substantial differences between B. cheleusis and the genotype, we consider the erection of a new, monotypic genus for cheleusis to be unwarranted. B. cheleusis has some major featrures in common with Oligosphaeridium Davey & Williams 1966 and Rigaudella Below 1982, but the affinities of Balcattia remain uncertain (Fensome et al., 1993, p. 117).
Comparison: Balcattia cheleusis differs from the genotype, B. cirrifera, in having an elongate cyst body and processes at the apical margins of the precingular paraplates, as opposed to processes on the apical series in the latter. B. cheleusis is also substantially larger than B. cirrifera. B. cheleusis is larger than B. cirribarbata Cookson & Eisenck 1982, which has also short nontabular processes in the central area of the cyst body. B. sp. A of Helby et al. (1987, figs. 271-K) is also significantly smaller than B. cheleusis. The former morphotype is paratabulate and lacks precingular processes.
Derivation of name: From the Greek, cheleusis meaning a netting and referring to the complex distal trabeculation of this species.
Holotype and type locality: Geological survey of Western Australia specimen F.49309, sideall core sample from Wanaea-3 well as 2964.0m. This specimen was figured as Rigaudella sp. B by Bint & Marshall (1994, fig. 5.15).
Statigrapjhical distribution: Balcattia cheleusis in confined to the Tithonian and ranges from the upper Dingodinium jurassicum Zone (5ai) to the lower Pseudoceratium iehiense Zone (4ciiib) (Foster, this volume; Helby & Partridge, in prep.).
Name not validly published: no description.
Taxonomic senior synonym: Balcattia cheleusis, according to Riding and Helby (2001g, p. 184).
(Riding and Helby, 2001g)
1994 Rigaudella sp. B ; Bint & Marshall, fig. 5.15.
Previous Australian usage
Emmetrocysta cheleusis Stevens & Helby (manuscript name)
Rigaudella separata – Parker (1986, p. 99-100, fig. 5.41, pl. 21, figs. 3-6)
Rigeuldella searata – Helby. MP 346 – Helby
Description: A species of Balcattia with a large, elongate ovoidal to subquadrangular cyst body. A small antapical protuberance may be present and the paracingular are is occasionally indented. The autophragm is moderately thin (0.5-1 µm), smooth to occasionally shagreenate or irregularly microscabrate. Intratabular processes, which are variable in morphology, are present on the precingular, postcingular, posterior intercalary and antapical paraplates. The hypocyst generally bears 7 processes and the epicyst has 5-6 processes . Processes are entirely absent in the paracingular area and the precingular and postcingular processes are inserted high and low respectively. This factor highlight the process-free equatorial region. The processes are variable in length, slender to wide (3-12 µm), mostly hollow, although some may be solid and other vacuolated. They are always distally expanded. At around midlength each process subdivides distally into slender, solid elements, which generally connect to the other processes and form a trabeculate ectophragmal layer. This expansion normally involves complex branching of the processes into fenestrate funnels. The processes may be interconnected by 1 to 5 slender trabeculate emanating from the distal parts of the processes. Alternatively, the distal part of the processes forms a complex, sheet-like fenestra ectophragm, which extents and connects to other processes. There are no trabeculate connections between the epicyst and hypocyst. All the specimens studied were loisthocysts and no free opercula were recognized.
Dimensions: (µm, n=26): Min.(Mean)Max.
Length of cyst incl. processes: 105(141)170
Length of cyst body (excl. processes): 56(69)94
Width of cyst incl. processes: 73(104)135
Width of cyst excl. processes: 37(54)78
Length of processes: 27(45)66
The measured specimens are from a convertional core sample from Mutineer-1B well at 3147.60m, sidewall core samples from Nancar-1 well at 3240.0m, Puratte-1 well at 172.0m, Scafell-1 well at 1421.0m and Wanaea-3 well at 2964.0m and ditch cuttings from Broome-1 Bore at 297.79m and Mindil-1 well between 3150.0m and 3155.0m
Comments: the distinctive species of Balcattia is large, and the size range is considerable. The processes haeve bipolar distribution and are positioned high on the precingular paraplate series and low on the postcingular paraplate series. All of the specimens studies were loisthocysts, and these were oriented by the position of the Archeopyle and the occasional presence of a small antapical protuberance. Where present, this protuberance bears the 1’’’’ processes. The processes are somewhat variable in morphology. Most are relatively long and slender; however, short and wide processes, although rare, were also observed. Only especially slender processes (1-2 µm in width) are solid, all other being hollow. On some specimens the precingular processes may be significantly shorted and those near the antapex. The specimens examined from the Broome-1 Bore do not exhibit distal trabeculation. This speices was originally informally assigned to Emmetrocysta Stover 1975 by Stevens & Helby (unpublished). However, that genus is characterized by paraplate-centered process complexes which are not joined by trabeculate strands and it is substantially smaller and consistently subspherical (Stover, 1975). Despite the substantial differences between B. cheleusis and the genotype, we consider the erection of a new, monotypic genus for cheleusis to be unwarranted. B. cheleusis has some major featrures in common with Oligosphaeridium Davey & Williams 1966 and Rigaudella Below 1982, but the affinities of Balcattia remain uncertain (Fensome et al., 1993, p. 117).
Comparison: Balcattia cheleusis differs from the genotype, B. cirrifera, in having an elongate cyst body and processes at the apical margins of the precingular paraplates, as opposed to processes on the apical series in the latter. B. cheleusis is also substantially larger than B. cirrifera. B. cheleusis is larger than B. cirribarbata Cookson & Eisenck 1982, which has also short nontabular processes in the central area of the cyst body. B. sp. A of Helby et al. (1987, figs. 271-K) is also significantly smaller than B. cheleusis. The former morphotype is paratabulate and lacks precingular processes.
Derivation of name: From the Greek, cheleusis meaning a netting and referring to the complex distal trabeculation of this species.
Holotype and type locality: Geological survey of Western Australia specimen F.49309, sideall core sample from Wanaea-3 well as 2964.0m. This specimen was figured as Rigaudella sp. B by Bint & Marshall (1994, fig. 5.15).
Statigrapjhical distribution: Balcattia cheleusis in confined to the Tithonian and ranges from the upper Dingodinium jurassicum Zone (5ai) to the lower Pseudoceratium iehiense Zone (4ciiib) (Foster, this volume; Helby & Partridge, in prep.).