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Sentusidinium erythrocomum
Sentusidinium erythrocomum Erkmen and Sarjeant, 1980
Holotype: Erkmen and Sarjeant, 1980, pl.4, fig.5
Paratypes: Erkmen and Sarjeant, 1980
Locus typicus: Tidmoor Point, Chickerell, near Weymouth, Dorset, England
Stratum typicum: Late Callovian
Original diagnosis: Erkmen and Sarjeant, 1980, p. 56
Cyst ovoidal to broadly ovoidal or almost spheroidal. Processes probably gonal, sutural and intratabular in position; they are moderately numerous (c. 150-200 on a complete cyst) and in general relatively slender (though a few processes on each individual are stouter than the others) . All processes are broad-based and taper to about half to two-thirds length, thereafter widening slightly and sometimes (though not consistently) flaring at the tip, imparting a capitate appearance. The processes are tabular and may be closed or open distally. The surface of the periphragm is moderately or coarsely shagreenate. Archaeopyle apical, with a distinct sulcal notch and with five or six accessory archaeopyle sutures, usually not extending far into the epitract. Operculum normally lost, but retained (wholly or partially) in a few instances.
Holotype: length 33 µm, breadth 25 µm, length of processes up to c. 3,5 µm. Paratype I: length (apex lacking) 38 µm, breadth 30 µm, length of processes up to 6 µm. Paratype II: length (apex lacking ) 26 µm, breadth 24 µm, processes up to 4,5 µm. Range of dimensions: length of complete cysts 31 - 42 µm (mean 35,5 µm ), length of cysts with apex lacking 18-38 µm (mean 29 µm), breadth 14-38 µm (mean 28 µm), maximum length of processes 2-6 µm (mean 4 µm ).
Under ordinary light, this species is readily confused with Sentusidinium: its characteristics--the coarse surface ornament and the tubular character of the processes -- are more readily seen under phase or Nomarski-interference contrast. However, the lower number of processes serves as a differentiating character at all times.
The tubular processes appear to be typically open distally, though their meagre diameter makes this hard to establish in many instances. Proximally, the processes appear not to be linked with the interior of the cyst. They are most often tubiform to buccinate, less commollly cylindrical, lagenate or tapering. The operculum is sometimes retained by a ventral connection (at the sulcus ?); much more often it is lost.
The positions of the processes may correspond in part to the boundaries of paraplates, though intratabular processes are certainly also present. The positions of paracingulum and parasulcus may sometimes be perceived from process alignment oh their margins: but we were unable to reconstruct the paratabulation. However, the number and position of the accessory archaeopyle sutures suggests that this species, like S. pilosum and S. creberbarbatum but unlike S. sparsibarbatum, belongs in the gonyaulacoid lineage.
Affinities:
Erkemen and Sarjeant, 1980, p. 56: The nature and greater relative length and number of the processes serve to distinguish S. erythrocomum from S. sparsibarbatum.
Holotype: Erkmen and Sarjeant, 1980, pl.4, fig.5
Paratypes: Erkmen and Sarjeant, 1980
Locus typicus: Tidmoor Point, Chickerell, near Weymouth, Dorset, England
Stratum typicum: Late Callovian
Original diagnosis: Erkmen and Sarjeant, 1980, p. 56
Cyst ovoidal to broadly ovoidal or almost spheroidal. Processes probably gonal, sutural and intratabular in position; they are moderately numerous (c. 150-200 on a complete cyst) and in general relatively slender (though a few processes on each individual are stouter than the others) . All processes are broad-based and taper to about half to two-thirds length, thereafter widening slightly and sometimes (though not consistently) flaring at the tip, imparting a capitate appearance. The processes are tabular and may be closed or open distally. The surface of the periphragm is moderately or coarsely shagreenate. Archaeopyle apical, with a distinct sulcal notch and with five or six accessory archaeopyle sutures, usually not extending far into the epitract. Operculum normally lost, but retained (wholly or partially) in a few instances.
Holotype: length 33 µm, breadth 25 µm, length of processes up to c. 3,5 µm. Paratype I: length (apex lacking) 38 µm, breadth 30 µm, length of processes up to 6 µm. Paratype II: length (apex lacking ) 26 µm, breadth 24 µm, processes up to 4,5 µm. Range of dimensions: length of complete cysts 31 - 42 µm (mean 35,5 µm ), length of cysts with apex lacking 18-38 µm (mean 29 µm), breadth 14-38 µm (mean 28 µm), maximum length of processes 2-6 µm (mean 4 µm ).
Under ordinary light, this species is readily confused with Sentusidinium: its characteristics--the coarse surface ornament and the tubular character of the processes -- are more readily seen under phase or Nomarski-interference contrast. However, the lower number of processes serves as a differentiating character at all times.
The tubular processes appear to be typically open distally, though their meagre diameter makes this hard to establish in many instances. Proximally, the processes appear not to be linked with the interior of the cyst. They are most often tubiform to buccinate, less commollly cylindrical, lagenate or tapering. The operculum is sometimes retained by a ventral connection (at the sulcus ?); much more often it is lost.
The positions of the processes may correspond in part to the boundaries of paraplates, though intratabular processes are certainly also present. The positions of paracingulum and parasulcus may sometimes be perceived from process alignment oh their margins: but we were unable to reconstruct the paratabulation. However, the number and position of the accessory archaeopyle sutures suggests that this species, like S. pilosum and S. creberbarbatum but unlike S. sparsibarbatum, belongs in the gonyaulacoid lineage.
Affinities:
Erkemen and Sarjeant, 1980, p. 56: The nature and greater relative length and number of the processes serve to distinguish S. erythrocomum from S. sparsibarbatum.