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Pseudoceratium robustum
Pseudoceratium robustum Michael, 1964
Originally Pseudoceratium, subsequently (and now) Pseudoceratium?. Questionable assignment: Bint (1986, p.145) as a problematic species.
Junior homonym: Pseudoceratium robustum Riding and Helby, 2001g.
Holotype: Michael, 1964, pl.2, fig.2
Age: Early Barremian
Original description:
Description. An intermediate to large, holocavate species of Pseudoceratium with a 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 ectophragm is thinner than the relatively thick, robus autophragm which is about 1-1.5 µm thick. The autophragm is densely covered by short, solid processes which are connected distally by a trabeculate/reticulate ectophragm. The processes flare slightly both proximally and distally and vary from 1 to 5 µm wide; the majority are 1-2µm in width. These elements are normally between 1 and 4 µm in height; the observed range is 1-11µm. Close to the antapex and at the distal parts of the horns, the processes are consistently 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 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 (µm, n=32) incl. ectophragm and horns where appropriate: Min. (Mean) Max.
Length of entire cyst: 97 (124) 136
Length of operculum: 45 (50) 65
Length of loisthocyst: 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 horn: 9 (21) 33
Length of right postcingular horn: 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. This 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 loisthocyst (Fig. 15).
Comparison. Pseudoceratium robustum differs from other species of Pseudoceratium in its thick autophragm and robust ectophragmal processes. Most other species have more numerous and slender autophragmal projections and are variably holocavate. The latter include the genotype, P. pelliferu 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 & Wiliams 1989, P. anaphrissum (Sarjeant 1966) Bint 1986, P. auleum Harding 1990 ex Harding in Williams et al. 1998, P. Brideaux 1971 and P. securigerum (Davey & Verdier 1974) Bint 1986. Pseudoceratium toveae Nøhr-Hansen 1993 is holocavate but the cavity between the autophragm and ectophragm is extremely small. Pseudoceratium gochtii Neale & Sarjeant 1962 has longer horns than P. robustum and the short spines arising from the autophragm indicate a certioid 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 seperata specific status of the basis of its extremely restricted range, disjunct from the range base of P. iehiense. The Albian species P. eisenackii (Davey 1969) Bint 1986 is characterized by extremely small horns and marginate ornamentation (Bint, 1986, pl.2 figs 14, 15). Pseudoceratium interiorense 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. Pseudoceratium 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 cutting sample in Mindil-1 well between 3150.00m and 3155.00m.
Stratigraphical distribution. Pseudoceratium robustum is confined to the Tithonian lower Pseudoceratium iehiense Zone (4ciiib) (Foster, this volume; Helby & Partridge, in prep.)
Originally Pseudoceratium, subsequently (and now) Pseudoceratium?. Questionable assignment: Bint (1986, p.145) as a problematic species.
Junior homonym: Pseudoceratium robustum Riding and Helby, 2001g.
Holotype: Michael, 1964, pl.2, fig.2
Age: Early Barremian
Original description:
Description. An intermediate to large, holocavate species of Pseudoceratium with a 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 ectophragm is thinner than the relatively thick, robus autophragm which is about 1-1.5 µm thick. The autophragm is densely covered by short, solid processes which are connected distally by a trabeculate/reticulate ectophragm. The processes flare slightly both proximally and distally and vary from 1 to 5 µm wide; the majority are 1-2µm in width. These elements are normally between 1 and 4 µm in height; the observed range is 1-11µm. Close to the antapex and at the distal parts of the horns, the processes are consistently 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 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 (µm, n=32) incl. ectophragm and horns where appropriate: Min. (Mean) Max.
Length of entire cyst: 97 (124) 136
Length of operculum: 45 (50) 65
Length of loisthocyst: 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 horn: 9 (21) 33
Length of right postcingular horn: 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. This 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 loisthocyst (Fig. 15).
Comparison. Pseudoceratium robustum differs from other species of Pseudoceratium in its thick autophragm and robust ectophragmal processes. Most other species have more numerous and slender autophragmal projections and are variably holocavate. The latter include the genotype, P. pelliferu 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 & Wiliams 1989, P. anaphrissum (Sarjeant 1966) Bint 1986, P. auleum Harding 1990 ex Harding in Williams et al. 1998, P. Brideaux 1971 and P. securigerum (Davey & Verdier 1974) Bint 1986. Pseudoceratium toveae Nøhr-Hansen 1993 is holocavate but the cavity between the autophragm and ectophragm is extremely small. Pseudoceratium gochtii Neale & Sarjeant 1962 has longer horns than P. robustum and the short spines arising from the autophragm indicate a certioid 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 seperata specific status of the basis of its extremely restricted range, disjunct from the range base of P. iehiense. The Albian species P. eisenackii (Davey 1969) Bint 1986 is characterized by extremely small horns and marginate ornamentation (Bint, 1986, pl.2 figs 14, 15). Pseudoceratium interiorense 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. Pseudoceratium 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 cutting sample in Mindil-1 well between 3150.00m and 3155.00m.
Stratigraphical distribution. Pseudoceratium robustum is confined to the Tithonian lower Pseudoceratium iehiense Zone (4ciiib) (Foster, this volume; Helby & Partridge, in prep.)