Back
Downiesphaeridium sarmentum
Downiesphaeridium sarmentum (Stancliffe, 1991, p.187-188, pl.1, figs.1-2; pl.2, fig.6; text-figs.5A-B) Masure in Fauconnier and Masure, 2004, p.196.
Originally Cleistosphaeridium, subsequently Impletosphaeridium, thirdly (and now) Downiesphaeridium. N.I.A.
Holotype: Stancliffe, 1991, pl.1, figs.1-2; text-figs.5A-B.
Age: Late Oxfordian.
Original description (Stancliff, 1991):
Derivation of name. Latin Sarmentum, twig or light branch, referring to the distal morphology of the processes.
Diagnosis. Skolochorate cyst with a sub spherical body; wall smooth to slightly granular. Processes isolated, nontabular, 28-40 in number, cover the body and are long (half to third of body width), hollow, generally straight, gently tapering distally and have slightly granular walls. Proximally the processes flare at the contact with the body but do not communicate with it. Distally the processes flare briefly at their tips, appear closed and have up to seven distal spines radiating from the process tip. Archeopyle apical with or without an attached operculum.
Type material. Holotype; slide GMUS E3 1 13/2, England Finder coordinate H37/0; Plate 1, Figures 1-2; Text-fig. 5. Paratype; slide GMUS E3 100/1, England Finder coordinate B37/4; Plate 2, Figure 6. Slides GMUS E3113/2 and GMUS E3100/1 are stored at the British Geological Survey, Keyworth, Nottinghamshire.
Dimensions (µm): Skye / Holotype / Paratype
Body length (no operc.): 26-37 / 26 / 27
Body breadth: 26-36 / 32 / 39
Length of processes: 10-19 / 10-13 / 13-19
Number of processes: 26-36 / 26 / 30
Number measured: 7(11)
Occurrence. In the present study, the new species was only found in the Skye sequence which is of Late Oxfordian Age (Amoeboceras rosenkrantzi Zone). The range could extend into the Early Kimmeridgian (Pictonia bavlei Zone) if the specimens found by Gitmez (1970) are assigned to the species.
Remarks. These cysts have a morphology close to that of C.? tribuliferum (Sarjeant 1962) Davey, Downie, Sarjeant & Williams 1966. Gitmez (1970, p. 288) included similar forms with a limited number of processes in the species but this is outside the range of the diagnosis as outlined by Sarjeant (1962, p. 487). A reexamination of these specimens would probably show that they can now be placed in C. sarmentum. No evidence of intergradation between these two species has been observed in the present study. The species is differentiated from C.? tribuliferum by its smaller number of processes, more complex distal spine morphology and the relatively shorter process length as compared to the body width. No other species of Cleistosphaeridium has a similar combination of features. Hvstrichosphaeridium petilum Gitmez 1970 has fewer processes which are intra tabular.
Originally Cleistosphaeridium, subsequently Impletosphaeridium, thirdly (and now) Downiesphaeridium. N.I.A.
Holotype: Stancliffe, 1991, pl.1, figs.1-2; text-figs.5A-B.
Age: Late Oxfordian.
Original description (Stancliff, 1991):
Derivation of name. Latin Sarmentum, twig or light branch, referring to the distal morphology of the processes.
Diagnosis. Skolochorate cyst with a sub spherical body; wall smooth to slightly granular. Processes isolated, nontabular, 28-40 in number, cover the body and are long (half to third of body width), hollow, generally straight, gently tapering distally and have slightly granular walls. Proximally the processes flare at the contact with the body but do not communicate with it. Distally the processes flare briefly at their tips, appear closed and have up to seven distal spines radiating from the process tip. Archeopyle apical with or without an attached operculum.
Type material. Holotype; slide GMUS E3 1 13/2, England Finder coordinate H37/0; Plate 1, Figures 1-2; Text-fig. 5. Paratype; slide GMUS E3 100/1, England Finder coordinate B37/4; Plate 2, Figure 6. Slides GMUS E3113/2 and GMUS E3100/1 are stored at the British Geological Survey, Keyworth, Nottinghamshire.
Dimensions (µm): Skye / Holotype / Paratype
Body length (no operc.): 26-37 / 26 / 27
Body breadth: 26-36 / 32 / 39
Length of processes: 10-19 / 10-13 / 13-19
Number of processes: 26-36 / 26 / 30
Number measured: 7(11)
Occurrence. In the present study, the new species was only found in the Skye sequence which is of Late Oxfordian Age (Amoeboceras rosenkrantzi Zone). The range could extend into the Early Kimmeridgian (Pictonia bavlei Zone) if the specimens found by Gitmez (1970) are assigned to the species.
Remarks. These cysts have a morphology close to that of C.? tribuliferum (Sarjeant 1962) Davey, Downie, Sarjeant & Williams 1966. Gitmez (1970, p. 288) included similar forms with a limited number of processes in the species but this is outside the range of the diagnosis as outlined by Sarjeant (1962, p. 487). A reexamination of these specimens would probably show that they can now be placed in C. sarmentum. No evidence of intergradation between these two species has been observed in the present study. The species is differentiated from C.? tribuliferum by its smaller number of processes, more complex distal spine morphology and the relatively shorter process length as compared to the body width. No other species of Cleistosphaeridium has a similar combination of features. Hvstrichosphaeridium petilum Gitmez 1970 has fewer processes which are intra tabular.