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Pseudoceratium robustum riding and helby 2001g
Pseudoceratium robustum Riding and Helby 2001g, p.208,210,212, figs.15A–L.
Name illegitimate — senior homonym: Pseudoceratium? robustum Michael, 1964.
Substitute name: Pseudoceratium australiense.
Originally Pseudoceratium robustum Riding and Helby (name illegitimate), subsequently (and now) Pseudoceratium australiense.
Holotype: Riding and Helby, 2001g, figs.15J–K.
Age: Tithonian.
Original description (Riding & Helby, 2001g):
Pseudoceratium robustum sp.nov. (Figs 15A-L)
Previous Australian usage:
Pseudoceratium iehiense (pars) – Helby
Pseudoceratium robustum sp. – Helby.
Pseudoceratium iehiense ‘macro’ – Morgan.
Description: an intermediate to large, holocavate species of Pseudoceratium with somewhat angular compressed ceratioid dorsoventral outline. Relatively large distally rounded apical and antapical horns are present. The single paracingular/postcingular horn is of variable length and may be greatly reduced. The outer layer of the ectophargm is thinner than the relatively thick, robust autophragm which is about 1-1.5 µm thick. The autophragm is densely covered short solid processes which are connected distally by a trabeculate/reticulate ectophragm. The processes flare slightly both proximally ad distally and vary from 1 to 5 µm wide; the majority are 1-2 µm in width. These elements are normally between 1 and 4 µm in height; the observed range is 1-11 µm. Close to the antapex and the distal parts of the horns, the processes are frequently longer. The processes are constantly shortest on the operculum. The ectophragm is reticulate, with ellipsoidal to subcircular fenestra between 2 and 6 µm in maximum diameter. The reticulation is often irregular, with the diameter and the shape of fenestra varying widely on individual specimens. Parasutural features are absent, except in some specimens where the paracingulum is indicated by low, subparallel ridges on the ectophragm.
Dimensions (in µm, n=32) incl. ectophragm and horns where appropriate: Min.(Mean)Max.
Length of the entire cyst: 97 (124) 136
Length of operculum: 45 (50) 65
Length of loistocyst: 74 (90) 105
Length of hypocyst incl. paracingulum: 47 (57) 69
Equatorial width: 61 (77) 87
Length of apical horn: 15 (25) 36
Length of antapical horns: 9 (21) 33
Length of right postcingular horns: 5 (11) 17
The measured specimens are from a sidewall core in Nancar-1 well at 3240.00m and ditch cuttings between 3150.00m and 3155.00m in Mindil-1 well. Additional specimens were studied from a sidewall core at 1418.00m in Scafell-1 well.
Comments: The distinctive species of Pseudoceratium is distinguished by its relatively large size, the thick, robust autophragm and the distinctive processes which support a vacuolated ectophragm. Most specimens observed were loistocysts (Fig. 15).
Comparison: Pseudoceratium robustum differs from other species of Pseudoceratium in its thick autophragm and robust ectophragmal processes. Most of the other species have more numerous and slender autophagmal projections and are variably holocavate. The latter include the genotype, P. pelliferum Gocht 1970, as well as P. retusum Brideaux 1977. Some representatives of the genus do not exhibit an ectophragm, for example P. almohadense (Below 1984) Lentin & Williams 1989, P. aulaeum Harding 1990 ex Harding in Williams et al. 1998, P. expolitum Brideaux 1971 and P. securigerum (Davey & Verdier 1974) Bint 1986. Pseudoceratium toveae Nøhr- Hansen 1993 is holocavate but the cavity between the autophragm and ectophargm is extremely small. Pseudoceratium gochtii Neale & Sarjeant 1962has longer horns than P. robustum and the short spines aring from the autophargms indicate a ceratioid paratabulation. Pseudoceratium iehiense Helby & May (in Helby, 1987) is extremely similar, but is marginally larger and has more numerous and slender ectophragmal processes. Arguably, P. robustum could be treated as a subspecies of P. iehiense. However, we prefer separate specific status on the basis of the extremely restricted range, disjunct from the range base of P. iehiense. The Albanian species P. eisenackii (Davey 1969) Bint 1986 is characterized by extremely small horns and marginate ornamentation (Bint 1986, pl. 2, figs. 14, 15). Pseudoceratium interioresne Bint 1986 is holocavate, but is unusually elongate and is cornucavate at the extremities of the horns. Holocavation is developed in P. iveri Nøhr- Hansen 1993 and P. plerum (Duxbury 1983) Bint 1986, but the pandasutural areas in these species are acavate. Nøhr- Hansen 1993 spitiense Jain & Garg 1984, is very similar to P. robustum, but the poor preservation of the former precludes a detailed comparison. The three horns in P. weymouthense Helby 1987 are extremely long, clearly differentiating it from P. robustum.
Derivation of name: From the Latin robustus, meaning hard and strong, referring to the thick, robust, ectophragmal processes.
Holotype and type locality: Figures 15J-K, CPC 36002, from a ditch cuttings sample in Mindil-1 well between 3150.00m and 3155.00m
Statigraphic distribution: Nøhr- Hansen 1993 robustum is confined to the Tithonian lower Pseudoceratium iehiense Zone (4ciiib) (Foster, this volume; Helby and Partridge, in prep.)
Name illegitimate — senior homonym: Pseudoceratium? robustum Michael, 1964.
Substitute name: Pseudoceratium australiense.
Originally Pseudoceratium robustum Riding and Helby (name illegitimate), subsequently (and now) Pseudoceratium australiense.
Holotype: Riding and Helby, 2001g, figs.15J–K.
Age: Tithonian.
Original description (Riding & Helby, 2001g):
Pseudoceratium robustum sp.nov. (Figs 15A-L)
Previous Australian usage:
Pseudoceratium iehiense (pars) – Helby
Pseudoceratium robustum sp. – Helby.
Pseudoceratium iehiense ‘macro’ – Morgan.
Description: an intermediate to large, holocavate species of Pseudoceratium with somewhat angular compressed ceratioid dorsoventral outline. Relatively large distally rounded apical and antapical horns are present. The single paracingular/postcingular horn is of variable length and may be greatly reduced. The outer layer of the ectophargm is thinner than the relatively thick, robust autophragm which is about 1-1.5 µm thick. The autophragm is densely covered short solid processes which are connected distally by a trabeculate/reticulate ectophragm. The processes flare slightly both proximally ad distally and vary from 1 to 5 µm wide; the majority are 1-2 µm in width. These elements are normally between 1 and 4 µm in height; the observed range is 1-11 µm. Close to the antapex and the distal parts of the horns, the processes are frequently longer. The processes are constantly shortest on the operculum. The ectophragm is reticulate, with ellipsoidal to subcircular fenestra between 2 and 6 µm in maximum diameter. The reticulation is often irregular, with the diameter and the shape of fenestra varying widely on individual specimens. Parasutural features are absent, except in some specimens where the paracingulum is indicated by low, subparallel ridges on the ectophragm.
Dimensions (in µm, n=32) incl. ectophragm and horns where appropriate: Min.(Mean)Max.
Length of the entire cyst: 97 (124) 136
Length of operculum: 45 (50) 65
Length of loistocyst: 74 (90) 105
Length of hypocyst incl. paracingulum: 47 (57) 69
Equatorial width: 61 (77) 87
Length of apical horn: 15 (25) 36
Length of antapical horns: 9 (21) 33
Length of right postcingular horns: 5 (11) 17
The measured specimens are from a sidewall core in Nancar-1 well at 3240.00m and ditch cuttings between 3150.00m and 3155.00m in Mindil-1 well. Additional specimens were studied from a sidewall core at 1418.00m in Scafell-1 well.
Comments: The distinctive species of Pseudoceratium is distinguished by its relatively large size, the thick, robust autophragm and the distinctive processes which support a vacuolated ectophragm. Most specimens observed were loistocysts (Fig. 15).
Comparison: Pseudoceratium robustum differs from other species of Pseudoceratium in its thick autophragm and robust ectophragmal processes. Most of the other species have more numerous and slender autophagmal projections and are variably holocavate. The latter include the genotype, P. pelliferum Gocht 1970, as well as P. retusum Brideaux 1977. Some representatives of the genus do not exhibit an ectophragm, for example P. almohadense (Below 1984) Lentin & Williams 1989, P. aulaeum Harding 1990 ex Harding in Williams et al. 1998, P. expolitum Brideaux 1971 and P. securigerum (Davey & Verdier 1974) Bint 1986. Pseudoceratium toveae Nøhr- Hansen 1993 is holocavate but the cavity between the autophragm and ectophargm is extremely small. Pseudoceratium gochtii Neale & Sarjeant 1962has longer horns than P. robustum and the short spines aring from the autophargms indicate a ceratioid paratabulation. Pseudoceratium iehiense Helby & May (in Helby, 1987) is extremely similar, but is marginally larger and has more numerous and slender ectophragmal processes. Arguably, P. robustum could be treated as a subspecies of P. iehiense. However, we prefer separate specific status on the basis of the extremely restricted range, disjunct from the range base of P. iehiense. The Albanian species P. eisenackii (Davey 1969) Bint 1986 is characterized by extremely small horns and marginate ornamentation (Bint 1986, pl. 2, figs. 14, 15). Pseudoceratium interioresne Bint 1986 is holocavate, but is unusually elongate and is cornucavate at the extremities of the horns. Holocavation is developed in P. iveri Nøhr- Hansen 1993 and P. plerum (Duxbury 1983) Bint 1986, but the pandasutural areas in these species are acavate. Nøhr- Hansen 1993 spitiense Jain & Garg 1984, is very similar to P. robustum, but the poor preservation of the former precludes a detailed comparison. The three horns in P. weymouthense Helby 1987 are extremely long, clearly differentiating it from P. robustum.
Derivation of name: From the Latin robustus, meaning hard and strong, referring to the thick, robust, ectophragmal processes.
Holotype and type locality: Figures 15J-K, CPC 36002, from a ditch cuttings sample in Mindil-1 well between 3150.00m and 3155.00m
Statigraphic distribution: Nøhr- Hansen 1993 robustum is confined to the Tithonian lower Pseudoceratium iehiense Zone (4ciiib) (Foster, this volume; Helby and Partridge, in prep.)