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Ctenidodinium complanatum
Ctenidodinium complanatum Harding, 1990
Name not validly published since lodgment of holotype not specified.
Holotype: Harding, 1990, pl.7, fig.1
Locus typicus: Speeton Clay, Speeton, England
Stratum typicum: Early Barremian
Original diagnosis: Harding, 1990, p. 25
Shape: Strongly oblate spheroid, ambitus thus rarely seen, subcircular apical or antapical views being more common. Epicyst is pronouncedly flattened with P forming a short apical prominence, hypocyst much larger than epicyst. Pronounced polar compression.
Phragma: Differentiated autophragm 1 Ám thick, consisting of a solid base layer surmounted by a thicker spongy granular layer. The cyst outer surface appears pitted and spongy. The parasutural septa are usually less than 3 Ám in height with denticulate margins. However, along the paracingulum the septa are higher, up to 8 Ám, varying from distally denticulate to deeply denticulate to fenestrate. Anterior cingular parasutural septum much lower than the posterior one.
Paratabulation: Metasert sexiform gonyaulacoid shown by denticulate septa. Paratabulation formula: 1pr, 4", 1a, 6"", 6c, 6""", 1"""", 1p, 5s. Due to oblate nature of cyst, apicals and antapical are large in relation to other paraplates. A is characteristically in contact with lu and B but not with 2 - metasert condition. lu is very small incidental paraplate (K) appears at B/C/4 triple junction.
Archaeopyle: Type Ea involving all epicystal paraplates. Operculum reduced so that the anterior cingular parasutural septum is left attached to the paracingulum. Simple polyplacoid operculum remains adnate to ai.
Paracingulum: Well developed, posterior parasutural septum up to 6 llm wide, may be in the form of a solid septum, distally denticulate, or with ovate fenestrations, or deeply incised into blade-like processes.
Parasulcus: L-type, reduced in size due to large Y. Flagellar scar prominent, deep elongate pit.
Dimensions: Diameter (50) 47 (45) µm. Specimens = 4 (4).
Affinities:
Harding, 1990, p.26: A rare but distinctive species, differing from the other species placed in the genus by its low denticulate parasutural septa and metasert condition. C. elegantulum a much larger form, is the only other member of the genus to be found at such a high stratigraphic level.
According to Benson (1985) the genus Ctenidodinium should be distinguished from Dichadogonyaulax by the possession of anterior intercalaries (incidentals of Evitt 1985), and an apically located preapical paraplate. However, Benson (1985) states that the preapicals of Dichadogonyaulax are "displaced ventrally" allowing A and B to touch each other. Although complying with the description of Ctenidodinium in C. complanatum paraplates A and B are in contact, perhaps indicating that this new species may be intermediate in morphology between the two genera. C. complanatum has asymmetrical-quadrate antapical and lu/li ventral arrangements, however, the apical arrangement does not conform to any of the schemes given by Helenes (1986). Dichadogonyaulax irregulare Benson 1985 differs from this new species in lacking incidental paraplates, having septal crests of different form and by having a laevigate periphragm.
Name not validly published since lodgment of holotype not specified.
Holotype: Harding, 1990, pl.7, fig.1
Locus typicus: Speeton Clay, Speeton, England
Stratum typicum: Early Barremian
Original diagnosis: Harding, 1990, p. 25
Shape: Strongly oblate spheroid, ambitus thus rarely seen, subcircular apical or antapical views being more common. Epicyst is pronouncedly flattened with P forming a short apical prominence, hypocyst much larger than epicyst. Pronounced polar compression.
Phragma: Differentiated autophragm 1 Ám thick, consisting of a solid base layer surmounted by a thicker spongy granular layer. The cyst outer surface appears pitted and spongy. The parasutural septa are usually less than 3 Ám in height with denticulate margins. However, along the paracingulum the septa are higher, up to 8 Ám, varying from distally denticulate to deeply denticulate to fenestrate. Anterior cingular parasutural septum much lower than the posterior one.
Paratabulation: Metasert sexiform gonyaulacoid shown by denticulate septa. Paratabulation formula: 1pr, 4", 1a, 6"", 6c, 6""", 1"""", 1p, 5s. Due to oblate nature of cyst, apicals and antapical are large in relation to other paraplates. A is characteristically in contact with lu and B but not with 2 - metasert condition. lu is very small incidental paraplate (K) appears at B/C/4 triple junction.
Archaeopyle: Type Ea involving all epicystal paraplates. Operculum reduced so that the anterior cingular parasutural septum is left attached to the paracingulum. Simple polyplacoid operculum remains adnate to ai.
Paracingulum: Well developed, posterior parasutural septum up to 6 llm wide, may be in the form of a solid septum, distally denticulate, or with ovate fenestrations, or deeply incised into blade-like processes.
Parasulcus: L-type, reduced in size due to large Y. Flagellar scar prominent, deep elongate pit.
Dimensions: Diameter (50) 47 (45) µm. Specimens = 4 (4).
Affinities:
Harding, 1990, p.26: A rare but distinctive species, differing from the other species placed in the genus by its low denticulate parasutural septa and metasert condition. C. elegantulum a much larger form, is the only other member of the genus to be found at such a high stratigraphic level.
According to Benson (1985) the genus Ctenidodinium should be distinguished from Dichadogonyaulax by the possession of anterior intercalaries (incidentals of Evitt 1985), and an apically located preapical paraplate. However, Benson (1985) states that the preapicals of Dichadogonyaulax are "displaced ventrally" allowing A and B to touch each other. Although complying with the description of Ctenidodinium in C. complanatum paraplates A and B are in contact, perhaps indicating that this new species may be intermediate in morphology between the two genera. C. complanatum has asymmetrical-quadrate antapical and lu/li ventral arrangements, however, the apical arrangement does not conform to any of the schemes given by Helenes (1986). Dichadogonyaulax irregulare Benson 1985 differs from this new species in lacking incidental paraplates, having septal crests of different form and by having a laevigate periphragm.