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Alterbidinium longicornutum
From Fensome et al., 2019:
Alterbidinium longicornutum, Roncaglia et al., 1999, p.297,299, fig.15, nos.1–5.
Holotype: Roncaglia et al., 1999, fig.15, no.5.
Age: Maastrichtian.
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Original description: [Roncaglia et al., 1999]:
Diagnosis:
Large, circumcavate, elongate peridinioid cyst, with one long apical horn and one long antapical horn. The periphragm is thin, smooth to finely granulate. The endocyst is centrally located, subcircular to oval, thin-walled and scabrate. The paracingulum is indicated by lateral projections and folds of the periphragm.
The archeopyle is intercalary, type I(2a); operculum attached posteriorly.
The paratabulation pattern is indicated by paracingulum and archeopyle only.
Description:
Cyst large, circumcavate, elongate to nearly biconical.
The pericyst bears one apical and one left antapical horn; sometimes a very reduced right antapical horn is present. The apical and left antapical horns are long (apical horn 25–50 µm; antapical horn 13–30 µm), conical, and terminate with acuminate to truncate tips.
The periphragm is thin, transparent, and smooth to finely granulate.
The endocyst is centrally located, subcircular to oval in ambital view, thin-walled, and scabrate; it is always clearly visible.
The paracingulum is indicated by lateral projections of the periphragm and by low, transverse equatorial folds (Figure 15.2). The lateral projections of the periphragm vary from faintly marked to very well developed.
The parasulcus is not indicated.
An intercalary, steno-deltaform archeopyle, type I(2a), is always present; the operculum is attached posteriorly.
Dimensions:
(in µm, 15 specimens measured): Holotype range: Overall length 192.6 118 (158) 200, Overall width 106.7 70 (89) 107, Length of endocyst 76.2 57 (73) 85, Width of endocyst 91.4 58 (75) 92
Affinities/Discussion:
Alterbidinium longicornutum differs from A. acutulum in having paracingular lateral projections and being much bigger than the latter. However, one paratype of A. acutulum figured by Wilson (1967, fig. 11) closely resembles the new species, and it may be conspecific with A. longicornutum. The new species differs from A. circulum and A. emulatum in having longer apical and antapical horns, bearing paracingular lateral projections, and being two to three times bigger. Furthermore, it differs from A. circulum in lacking indications of paratabulation on the dorsal surface. Alterbidinium longicornutum differs from A. dictyotum in lacking a reticulate periphragm and being larger. It differs from A.? distinctum in lacking longitudinal folds in the periphragm between the apical and antapical horns, in lacking indication of parasulcus, and in being larger. Alterbidinium longicornutum differs from A. montanaense and A. pilosum in being circumcavate and bigger; it differs further from A. montanaense in lacking indications of paratabulation, and from A. pilosum in lacking paracingular spines. Alterbidinium longicornutum resembles A.? pentaradiatum in size and archeopyle shape, but lacks a well-developed right antapical horn, striate periphragm, low and parallel paracingular ridges, and indication of parasulcus.
Alterbidinium longicornutum, Roncaglia et al., 1999, p.297,299, fig.15, nos.1–5.
Holotype: Roncaglia et al., 1999, fig.15, no.5.
Age: Maastrichtian.
---------------------------------------------------------------------------------------------------
Original description: [Roncaglia et al., 1999]:
Diagnosis:
Large, circumcavate, elongate peridinioid cyst, with one long apical horn and one long antapical horn. The periphragm is thin, smooth to finely granulate. The endocyst is centrally located, subcircular to oval, thin-walled and scabrate. The paracingulum is indicated by lateral projections and folds of the periphragm.
The archeopyle is intercalary, type I(2a); operculum attached posteriorly.
The paratabulation pattern is indicated by paracingulum and archeopyle only.
Description:
Cyst large, circumcavate, elongate to nearly biconical.
The pericyst bears one apical and one left antapical horn; sometimes a very reduced right antapical horn is present. The apical and left antapical horns are long (apical horn 25–50 µm; antapical horn 13–30 µm), conical, and terminate with acuminate to truncate tips.
The periphragm is thin, transparent, and smooth to finely granulate.
The endocyst is centrally located, subcircular to oval in ambital view, thin-walled, and scabrate; it is always clearly visible.
The paracingulum is indicated by lateral projections of the periphragm and by low, transverse equatorial folds (Figure 15.2). The lateral projections of the periphragm vary from faintly marked to very well developed.
The parasulcus is not indicated.
An intercalary, steno-deltaform archeopyle, type I(2a), is always present; the operculum is attached posteriorly.
Dimensions:
(in µm, 15 specimens measured): Holotype range: Overall length 192.6 118 (158) 200, Overall width 106.7 70 (89) 107, Length of endocyst 76.2 57 (73) 85, Width of endocyst 91.4 58 (75) 92
Affinities/Discussion:
Alterbidinium longicornutum differs from A. acutulum in having paracingular lateral projections and being much bigger than the latter. However, one paratype of A. acutulum figured by Wilson (1967, fig. 11) closely resembles the new species, and it may be conspecific with A. longicornutum. The new species differs from A. circulum and A. emulatum in having longer apical and antapical horns, bearing paracingular lateral projections, and being two to three times bigger. Furthermore, it differs from A. circulum in lacking indications of paratabulation on the dorsal surface. Alterbidinium longicornutum differs from A. dictyotum in lacking a reticulate periphragm and being larger. It differs from A.? distinctum in lacking longitudinal folds in the periphragm between the apical and antapical horns, in lacking indication of parasulcus, and in being larger. Alterbidinium longicornutum differs from A. montanaense and A. pilosum in being circumcavate and bigger; it differs further from A. montanaense in lacking indications of paratabulation, and from A. pilosum in lacking paracingular spines. Alterbidinium longicornutum resembles A.? pentaradiatum in size and archeopyle shape, but lacks a well-developed right antapical horn, striate periphragm, low and parallel paracingular ridges, and indication of parasulcus.