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Ctenidodinium planocristatum
Ctenidodinium planocristatum Riding and Helby, 2001d, p.72-73, figs.5A-O.
Holotype: Riding and Helby, 2001d, fig.5J.
Age: Mid-Late Callovian.
(Riding and Helby, 2001d):
Derivation of name: From the Latoin planus, meaning smooth or even, and cristatus, meaning crested. This refers to the largely smooth, low, parasutural ridges/crests of this species.
Holotype and type locality: Figure 5J, CPC 35379, Undan-4 well, conventional core sample at 3135.24m.
Stratigraphical distribution: Ctenidodinium planocristatum has been recorded from th Middle-Upper Callovian strata of the timor Sea region. It ranges from the Wanaea digitate Zone (7bi) to the middle Rigaudella aemula Zone (7aiia) and is most prominent, providing biostratigraphically useful acmes, in the middle Rigaudella aemula Zone (7aiiaii) (Foster, this volume; Helby & Partridge, in prep.)
Description: a species of Ctenidodinium, subsphaerical in outlne, with or withour a small apical protuberance. Autophragm relatively thin, smooth, microgranulate and/or irregularly microgranulate. Paratabulation fully indicated by low parasutural ridges and/or crests which are dominantly distally smooth and even in height. The parasutural ridges/crests may occasionally be fenestrate. Rarely the fenestrae may be reduced, thereby producing irregularly denticulate parasutural crests. When developed. The denticles are short, solid and distally pointed.
Dimensions (µm; n=32): Min.(mean)Max.
Length of cyst: 69(79)93
Width of cyst: 67(78)96
Height of parasutural ridges/crests: 1(2)4
The measured specimens are all from conventional core form Undan-4 well as 3135.24m.
Comments: Ctenidodinium planocristatum is characterized by its equant, subspherical outline and the mainly distally smooth parasutural ridges or crests. These ridges are occasionally irregularly fenestrate, The distal parts of the fenestrate crests may be lost, thereby producing an irregular denticulare ornament. However the overall impression is that of a species devoid of larger ornamentational elements. The parasutural crests surrounding the paracingulum are normally prominent.
Comparison: Ctenidodinium planocristatum differs from the other species of Ctenidodinium by the low, largely smooth, parasutural ridges or crests. The majority of other representatives of the genus have ornamentation in the form of processes or denticules surmounting the parasutures and inserted relatively densely (Woollam, 1983; Benson 1985; see Comparison section for C. fuscibasilarum). Ctenidodinium coronatum exhibits high , distally smooth parasutural crests, thus is comparable to C. planocristatum. The crests of C. coronatum are confinet to the hypocyst and are significantly higher and more prominent than the parasutural ornament of C. planocristatum (see Prauss, 1989, fig. 12). Ctenidodinium? Schizoblatum has parasutural crests devoid of processes, yet is smaller than C. planocristatum and has parasutural crests which are serrated and split (Norris, 1965). The Late Jurassic Ctenidodinium chondrum also has low, smooth parasutural crests, but is markedly shorter, although almost as wide as C. planocristatum, and is granulate. Furthermore, C. planocristatum never bears processes. Representatives of Korystocysta Woollam 1983, such as K. gochtii (Sarjeant 1976) Woollam 1983 and K. kettonensis (Sarjeant 1976) Woollam 1983, differ from C. planocristatum in lacking fenestrate ridges/crests. However, Sarjeant (1976, fig. 3) suggested that the parasutural features on K. kettonensis may bear dinticles/small ‘spinelets’ in the antapical area.
Holotype: Riding and Helby, 2001d, fig.5J.
Age: Mid-Late Callovian.
(Riding and Helby, 2001d):
Derivation of name: From the Latoin planus, meaning smooth or even, and cristatus, meaning crested. This refers to the largely smooth, low, parasutural ridges/crests of this species.
Holotype and type locality: Figure 5J, CPC 35379, Undan-4 well, conventional core sample at 3135.24m.
Stratigraphical distribution: Ctenidodinium planocristatum has been recorded from th Middle-Upper Callovian strata of the timor Sea region. It ranges from the Wanaea digitate Zone (7bi) to the middle Rigaudella aemula Zone (7aiia) and is most prominent, providing biostratigraphically useful acmes, in the middle Rigaudella aemula Zone (7aiiaii) (Foster, this volume; Helby & Partridge, in prep.)
Description: a species of Ctenidodinium, subsphaerical in outlne, with or withour a small apical protuberance. Autophragm relatively thin, smooth, microgranulate and/or irregularly microgranulate. Paratabulation fully indicated by low parasutural ridges and/or crests which are dominantly distally smooth and even in height. The parasutural ridges/crests may occasionally be fenestrate. Rarely the fenestrae may be reduced, thereby producing irregularly denticulate parasutural crests. When developed. The denticles are short, solid and distally pointed.
Dimensions (µm; n=32): Min.(mean)Max.
Length of cyst: 69(79)93
Width of cyst: 67(78)96
Height of parasutural ridges/crests: 1(2)4
The measured specimens are all from conventional core form Undan-4 well as 3135.24m.
Comments: Ctenidodinium planocristatum is characterized by its equant, subspherical outline and the mainly distally smooth parasutural ridges or crests. These ridges are occasionally irregularly fenestrate, The distal parts of the fenestrate crests may be lost, thereby producing an irregular denticulare ornament. However the overall impression is that of a species devoid of larger ornamentational elements. The parasutural crests surrounding the paracingulum are normally prominent.
Comparison: Ctenidodinium planocristatum differs from the other species of Ctenidodinium by the low, largely smooth, parasutural ridges or crests. The majority of other representatives of the genus have ornamentation in the form of processes or denticules surmounting the parasutures and inserted relatively densely (Woollam, 1983; Benson 1985; see Comparison section for C. fuscibasilarum). Ctenidodinium coronatum exhibits high , distally smooth parasutural crests, thus is comparable to C. planocristatum. The crests of C. coronatum are confinet to the hypocyst and are significantly higher and more prominent than the parasutural ornament of C. planocristatum (see Prauss, 1989, fig. 12). Ctenidodinium? Schizoblatum has parasutural crests devoid of processes, yet is smaller than C. planocristatum and has parasutural crests which are serrated and split (Norris, 1965). The Late Jurassic Ctenidodinium chondrum also has low, smooth parasutural crests, but is markedly shorter, although almost as wide as C. planocristatum, and is granulate. Furthermore, C. planocristatum never bears processes. Representatives of Korystocysta Woollam 1983, such as K. gochtii (Sarjeant 1976) Woollam 1983 and K. kettonensis (Sarjeant 1976) Woollam 1983, differ from C. planocristatum in lacking fenestrate ridges/crests. However, Sarjeant (1976, fig. 3) suggested that the parasutural features on K. kettonensis may bear dinticles/small ‘spinelets’ in the antapical area.