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Cavatodissiliodinium hansgochtii
Cavatodissiliodinium hansgochtii, Feist-Burkhardt and Monteil, 2001, p.52,54,56, fig.2, nos.1-7; fig.18, nos.1-8, fig.19, no.2.
Holotype: Feist-Burkhardt and Monteil, 2001, fig.2, nos.6-7; fig.18, nos.7-8; fig.19, no.2.
Age: Early Bajocian.
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Original description: [Feist-Burkhardt and Monteil, 2001]:
Description:
Cyst proximate, subspherical, cavate. Cyst wall composed of two layers, a thin endophragm and a thinner periphragm in relatively loose contact. Folds in the periphragm are abundant, thus no distinct pericoel areas are developed. Endophragm ornamented by unevenly distributed grana and irregular verrucae of different size. Periphragm psilate to finely granulate.
Archeopyle precingular, compound, variable, formed by the loss of up to 5 precingular paraplates (1’’-5’’), opercular pieces free, adherent partially detached or adherent in place.
Paratabulation generally indicated only by archeopyle when precingular paraplates are separated or displaced. Occasionally paratabulation may be indicated by folds in the periphragm or reduced ornamentation near the paraplate boundaries. Apical paraplates remain attached to the hypocyst by an isthmus consisting of the paraplates 6’’ as, and, generally, 1’’. Epicystal paratabulation gonyaulacacean, partial paratabulation formula: ?pr, 4’, ?1-2a, 6’’, as.
Precingular paraplates of sub-equal size and stalked, except for 3’’. Paracingulum usually not expressed, sometimes indicated by parallel transverse structures, or reduced of ornamentation of the cingular paraplate. Parasulcus generally not marked.
Dimensions:
Holotype 71 µm wide at the paracingulum in lateral view (compressed specimen in Eukitt slide); range in Eukitt slides: 62-71 µm wide at paracingulum (compressed specimens)
Remarks:
In contrast to e.g. Dissiliodinium species, the margins of isolated precingular paraplates and the apical cap are not very sharply drawn, but somewhat irregular and not well-defined. Therefore there remain some uncertainties on the exact number and the outline of dorsal anterior intercalary paraplates present in this species. The specimens of Fig. 18/5 shows a precingular paraplate 4’’ that is camerate and therefore indicating the presence of at least one dorsal anterior intercalary paraplate.
Affinities:
Specimens of Cavatodissiliodinium hansgochtii n.g. et n.sp. are easily recognizable by their combination of characteristics: (1) a multi-plate precingular archeopyle, (2) the cavate cyst wall and (3) the irregularly granulate to verrucate endophragm. It differs from species of Dissiliodinium in being cavate instead of acavate. Species if the cavate genera Scriniodinium and Endoscrinium differ from Cavatodissiliodinium hansgochtii n.g et n.sp. in their archeopyle type. These genera have a 1P archeopyle, where only the precingular paraplate 3’’ is lost in archeopyle formation.
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Stratigraphical and geographical occurrence: This study; SW-Germany, Early Bajocian, Laeviuscula and Sauzei Zone; NW-Germany; Switzerland Préalpes Médianes, Early Bajocian. The species is considered a most useful Stratigraphical marker for the Early Bajocian Laeviuscula and Sauzei Zones. It often occurs in high numbers and is associated with other early gonyaulacacean cyst species belonging to the genera Batiacasphaera, Dissiliodinium, Durotrigia, Kallosphaeridium and Sentusidinium. Recognition of Cavatodissiliodinium hansgochtii is very easy since it is the first and only cavate gonyaulacacean species present in early Middle Jurassic assembles.
Holotype: Feist-Burkhardt and Monteil, 2001, fig.2, nos.6-7; fig.18, nos.7-8; fig.19, no.2.
Age: Early Bajocian.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Feist-Burkhardt and Monteil, 2001]:
Description:
Cyst proximate, subspherical, cavate. Cyst wall composed of two layers, a thin endophragm and a thinner periphragm in relatively loose contact. Folds in the periphragm are abundant, thus no distinct pericoel areas are developed. Endophragm ornamented by unevenly distributed grana and irregular verrucae of different size. Periphragm psilate to finely granulate.
Archeopyle precingular, compound, variable, formed by the loss of up to 5 precingular paraplates (1’’-5’’), opercular pieces free, adherent partially detached or adherent in place.
Paratabulation generally indicated only by archeopyle when precingular paraplates are separated or displaced. Occasionally paratabulation may be indicated by folds in the periphragm or reduced ornamentation near the paraplate boundaries. Apical paraplates remain attached to the hypocyst by an isthmus consisting of the paraplates 6’’ as, and, generally, 1’’. Epicystal paratabulation gonyaulacacean, partial paratabulation formula: ?pr, 4’, ?1-2a, 6’’, as.
Precingular paraplates of sub-equal size and stalked, except for 3’’. Paracingulum usually not expressed, sometimes indicated by parallel transverse structures, or reduced of ornamentation of the cingular paraplate. Parasulcus generally not marked.
Dimensions:
Holotype 71 µm wide at the paracingulum in lateral view (compressed specimen in Eukitt slide); range in Eukitt slides: 62-71 µm wide at paracingulum (compressed specimens)
Remarks:
In contrast to e.g. Dissiliodinium species, the margins of isolated precingular paraplates and the apical cap are not very sharply drawn, but somewhat irregular and not well-defined. Therefore there remain some uncertainties on the exact number and the outline of dorsal anterior intercalary paraplates present in this species. The specimens of Fig. 18/5 shows a precingular paraplate 4’’ that is camerate and therefore indicating the presence of at least one dorsal anterior intercalary paraplate.
Affinities:
Specimens of Cavatodissiliodinium hansgochtii n.g. et n.sp. are easily recognizable by their combination of characteristics: (1) a multi-plate precingular archeopyle, (2) the cavate cyst wall and (3) the irregularly granulate to verrucate endophragm. It differs from species of Dissiliodinium in being cavate instead of acavate. Species if the cavate genera Scriniodinium and Endoscrinium differ from Cavatodissiliodinium hansgochtii n.g et n.sp. in their archeopyle type. These genera have a 1P archeopyle, where only the precingular paraplate 3’’ is lost in archeopyle formation.
-----------------------------------------------------------------
Stratigraphical and geographical occurrence: This study; SW-Germany, Early Bajocian, Laeviuscula and Sauzei Zone; NW-Germany; Switzerland Préalpes Médianes, Early Bajocian. The species is considered a most useful Stratigraphical marker for the Early Bajocian Laeviuscula and Sauzei Zones. It often occurs in high numbers and is associated with other early gonyaulacacean cyst species belonging to the genera Batiacasphaera, Dissiliodinium, Durotrigia, Kallosphaeridium and Sentusidinium. Recognition of Cavatodissiliodinium hansgochtii is very easy since it is the first and only cavate gonyaulacacean species present in early Middle Jurassic assembles.