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Phelodinium exilicornutum
Phelodinium exilicornutum Smith, 1992
Holotype: Smith, 1992, fig.8c
Locus typicus: Cape Lamb, Vega Island, James Ross Island Area, Antarctica
Stratum typicum: Late Campanian-Early Maastrichtian
Diagnosis: Smith, 1992, p. 348
A species of Phelodinium which is approximately pentagonal in shape with one slender apical horn and two slender antapical horns. It has small cornucavations. The periphragm bears numerous longitudinal wrinkles with the paracingulum being indicated by lateral folding.
Description: Smith, 1992, p. 348
The cyst has a pentagonal ambitus with straight sides. It bears one long apical horn (c.55 µm) and two shorter equal antapical horns (c.25-30 µm). Often the specimens have one or more of the horns broken. The cyst is cornucavate with small periocoels at the horn bases. The endophragm and periphragm are closely appressed elsewhere. The endophragm is thick (c.1.5 µm) and smooth, the periphragm is thinner (<1 µm), slightly scabrate, and normally highly longitudinally wrinkled giving the cyst a pseudo-striate appearance. The paracingulum is indicated by prominent lateral folding. No other paratabulation is indicated other than the archaeopyle. The archaeopyle is normally iso-deltaform intercalary (2a) and large. The operculum is free.
Dimensions (µm)MinMeanMax
Overall length95116162
Overall breadth505765
Endophragm length687480
Endophragm breadth505765
Specimens measured: 8
Remarks and comparisons: Smith, 1992, p. 348
Phelodinium exilicornutum sp. nov. superficially resembles species of Cerodinium in shape and in possessing a longitudinally wrinkled periphragm. However, because of the restricted cornucavation, it is better accomodated within Phelodinium. Cerodinium boloniense is morphologically comparable to P. exilicornutum but lacks the long apical horn, and has a more rounded ambitus and more extensive cavations. Phelodinium magnificum is similarbut has much shorter and broader horns. Cerodinium cordiferum is also similar in character but has a more extensive cavation and an inverted heart-shaped endocyst. Octodinium askiniae is morphologically close to this species, but is differentiated by having an octoform (eight sided) archaeopyle. A possible morphological gradation between O. askiniae and P. exilicornutum seems to be possible as rare specimens recorded here possess a seven sided archaeopyle. This style of archaeopyle has one side in the characteristic shape of O. askiniae, and the other side in a standard deltaform shape. Phelodinium exilicornutum sp. nov. has previously been recorded from Vega and Cockburn islands by Askin (1988, 1991) as Phelodinium sp . (R.A. Askin, personal communication 1991).
Holotype: Smith, 1992, fig.8c
Locus typicus: Cape Lamb, Vega Island, James Ross Island Area, Antarctica
Stratum typicum: Late Campanian-Early Maastrichtian
Diagnosis: Smith, 1992, p. 348
A species of Phelodinium which is approximately pentagonal in shape with one slender apical horn and two slender antapical horns. It has small cornucavations. The periphragm bears numerous longitudinal wrinkles with the paracingulum being indicated by lateral folding.
Description: Smith, 1992, p. 348
The cyst has a pentagonal ambitus with straight sides. It bears one long apical horn (c.55 µm) and two shorter equal antapical horns (c.25-30 µm). Often the specimens have one or more of the horns broken. The cyst is cornucavate with small periocoels at the horn bases. The endophragm and periphragm are closely appressed elsewhere. The endophragm is thick (c.1.5 µm) and smooth, the periphragm is thinner (<1 µm), slightly scabrate, and normally highly longitudinally wrinkled giving the cyst a pseudo-striate appearance. The paracingulum is indicated by prominent lateral folding. No other paratabulation is indicated other than the archaeopyle. The archaeopyle is normally iso-deltaform intercalary (2a) and large. The operculum is free.
Dimensions (µm)MinMeanMax
Overall length95116162
Overall breadth505765
Endophragm length687480
Endophragm breadth505765
Specimens measured: 8
Remarks and comparisons: Smith, 1992, p. 348
Phelodinium exilicornutum sp. nov. superficially resembles species of Cerodinium in shape and in possessing a longitudinally wrinkled periphragm. However, because of the restricted cornucavation, it is better accomodated within Phelodinium. Cerodinium boloniense is morphologically comparable to P. exilicornutum but lacks the long apical horn, and has a more rounded ambitus and more extensive cavations. Phelodinium magnificum is similarbut has much shorter and broader horns. Cerodinium cordiferum is also similar in character but has a more extensive cavation and an inverted heart-shaped endocyst. Octodinium askiniae is morphologically close to this species, but is differentiated by having an octoform (eight sided) archaeopyle. A possible morphological gradation between O. askiniae and P. exilicornutum seems to be possible as rare specimens recorded here possess a seven sided archaeopyle. This style of archaeopyle has one side in the characteristic shape of O. askiniae, and the other side in a standard deltaform shape. Phelodinium exilicornutum sp. nov. has previously been recorded from Vega and Cockburn islands by Askin (1988, 1991) as Phelodinium sp . (R.A. Askin, personal communication 1991).