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Balcattia cheleusis
Balcattia cheleusis, Riding, Helby and Stevens in Riding and Helby, 2001g, p. 184,186, figs.3A-P.
Holotype: Riding and Helby, 2001g, figs.3E-F.
Stratigraphical distribution: confined to the Tithonian; ranges from the upper Dingodinium jurassicum Zone (5ai) to the lower Pseudoceratium iehiense Zone (4ciiib) (Foster, this volume; Helby & Partridge, in prep.).
Age: Tithonian.
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Original description: [Riding & Helby, 2001g]:
Description:
A species of Balcattia with a large, elongate ovoidal to subquadrangular cyst body. A small antapical perturbance may be present and the paracingular area 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 anatapical paraplates. The hypocyst generally bears 7 processes and the epicyst had 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 highlights the process-free equatorial region. The processes are variable in length (see dimensions, below), slender to wide (3-12 µm), mostly hollow, although some may be solid and other vacuolated. They are always distally expanded. At around mid-length each process subdivides distally into slender, solid processes, 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, fenestrate ectophragm, which extends and connects to the other processes. There are no trabeculate connections between the epicyst and hypocyst. All the specimens studied were loisthocysts and not free opercula were recognized.
Dimensions:
(µm, n=26): Min(Mean)Max
Length of the 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 the cyst excl. processes: 37(45)66
The measured specimens are from a conventional core sample from Mutineer-1B well at 3147.60m, sidewall core sample from Nancar-1 well at 3240.00m, Puratte-1 well at 172.00m, Scafell-1 well at 1421.00m and Wanaea-3 well at 2964.00m and a ditch cuttings from Broome-1 Bore at 297.79m and Mindil-1 well between 3150.00m and 3155.00m.
Remarks/Comments: This distinctive species of Balcattia is large, and the size range is considerable. The processes have bipolar distribution and are positioned high on the precingular paraplate series and low on the postcingular paraplate series (Fig. 3). All of the specimens studies were loistocysts, 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’’’’ process. 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 others being hollow. Of some specimens the precingular processes may be significantly shorter than those near the antapex (specimens not illustrated). The specimens examined from Broome-1 Bore do not exhibit distal trabeculation. This species was originally informally assigned to Emmetrocysta (Stover, 1975) by Stevens & Helby characterized by paraplate-centred process 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 features in common with Oligosphaeridium (Davey & Williams, 1966) and Rigaudella (Below, 1982), but the affinities of Balcattia remain uncertain (Fensome et al., 1993, p. 117).
Affinities/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 in the apical series in the latter. Balcattia cheleusis is also substantially larger than B. cirrifera. Balcattia cheleusis is larger than B. cirribarbata (Cookson & Eisenack, 1982), which also has short, ontabular processes in the central area of the cyst body. Balcattia sp. A of Helby et al. (1987, figs 27I-K) is also significantly smaller than B. cheleusis. The former morphotype is paratabulate and lack precingular processes.
Holotype: Riding and Helby, 2001g, figs.3E-F.
Stratigraphical distribution: confined to the Tithonian; ranges from the upper Dingodinium jurassicum Zone (5ai) to the lower Pseudoceratium iehiense Zone (4ciiib) (Foster, this volume; Helby & Partridge, in prep.).
Age: Tithonian.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Riding & Helby, 2001g]:
Description:
A species of Balcattia with a large, elongate ovoidal to subquadrangular cyst body. A small antapical perturbance may be present and the paracingular area 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 anatapical paraplates. The hypocyst generally bears 7 processes and the epicyst had 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 highlights the process-free equatorial region. The processes are variable in length (see dimensions, below), slender to wide (3-12 µm), mostly hollow, although some may be solid and other vacuolated. They are always distally expanded. At around mid-length each process subdivides distally into slender, solid processes, 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, fenestrate ectophragm, which extends and connects to the other processes. There are no trabeculate connections between the epicyst and hypocyst. All the specimens studied were loisthocysts and not free opercula were recognized.
Dimensions:
(µm, n=26): Min(Mean)Max
Length of the 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 the cyst excl. processes: 37(45)66
The measured specimens are from a conventional core sample from Mutineer-1B well at 3147.60m, sidewall core sample from Nancar-1 well at 3240.00m, Puratte-1 well at 172.00m, Scafell-1 well at 1421.00m and Wanaea-3 well at 2964.00m and a ditch cuttings from Broome-1 Bore at 297.79m and Mindil-1 well between 3150.00m and 3155.00m.
Remarks/Comments: This distinctive species of Balcattia is large, and the size range is considerable. The processes have bipolar distribution and are positioned high on the precingular paraplate series and low on the postcingular paraplate series (Fig. 3). All of the specimens studies were loistocysts, 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’’’’ process. 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 others being hollow. Of some specimens the precingular processes may be significantly shorter than those near the antapex (specimens not illustrated). The specimens examined from Broome-1 Bore do not exhibit distal trabeculation. This species was originally informally assigned to Emmetrocysta (Stover, 1975) by Stevens & Helby characterized by paraplate-centred process 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 features in common with Oligosphaeridium (Davey & Williams, 1966) and Rigaudella (Below, 1982), but the affinities of Balcattia remain uncertain (Fensome et al., 1993, p. 117).
Affinities/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 in the apical series in the latter. Balcattia cheleusis is also substantially larger than B. cirrifera. Balcattia cheleusis is larger than B. cirribarbata (Cookson & Eisenack, 1982), which also has short, ontabular processes in the central area of the cyst body. Balcattia sp. A of Helby et al. (1987, figs 27I-K) is also significantly smaller than B. cheleusis. The former morphotype is paratabulate and lack precingular processes.