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Alterbidinium ellentonense
From Fensome et al., 2019:
Alterbidinium ellentonense, Lucas-Clark, 2006, p.189–190, pl.1, figs.3–6.
Holotype: Lucas-Clark, 2006, pl.1, figs.3–4.
Age: Paleocene.
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Original description: [Lucas-Clark, 2006]:
Diagnosis:
Medium sized pale peridinioid. Bicavate or apically cavate in the epicyst and cornucavate in the hypocyst. Distinguished by pronounced apical cavation and variable archeopyle. Ovoidal in shape with unequal antapical horns.
Archeopyle either 2a with sutures around 4'' or combination of 2a and 4''.
Tabulation shown only by archeopyle and weak folds indicating the cingulum.
Description:
Medium size, proximate peridiniacean cysts, bicavate or cornucavate in the hypocyst and apically cavate in the epicyst, with a short, wide apical horn and two short antapical horns. Left antapical horn longer and better developed than right, which is greatly reduced.
Endocyst ovoidal to pear-shaped in outline; endophragm smooth, about equal in thickness to periphragm, the two walls appressed around the archeopyle and the cingulum, and on the hypocyst except beneath horns.
Pericyst outline peridinioid, usually wider in hypocystal area; lateral margins convex; antapical margin straight to slightly convex except for horns. Periphragm thin, surface smooth or with tiny, randomly scattered granules.
Tabulation indicated by archeopyle and cingulum only.
Cingulum indicated by weak folding.
Archeopyle type variable: I+P (2a and 4'') or type I, sometimes with accessory archeopyle sutures on either side of plate 4''. Plate 2a is hexagonal, eurythetaform. If archeopyle is type I + P, the operculum is adnate along the posterior margin of 4''. If the archeopyle is type I, the operculum is free. The archeopyle appears to penetrate both cyst walls, but the exact relationship of endoarcheopyle and periarcheopyle is uncertain. Cingulum weakly indicated by folds in the periphragm. Sulcus not indicated. Accumulation bodies sometimes present.
Dimensions:
Length, 90–120 µm; width, 60–70 µm (4 specimens measured).
Remarks:
Unusual features of Alterbidinium ellentonense sp. nov. in terms of this genus include bicavation or cornucavation, rather than circumcavation. They also include a somewhat more rectangular/ovoidal shape, and only a moderate difference between the development of antapical horns. Alterbidinium ellentonense sp. nov. could be assigned to Senegalinium, except that it consistently has unequal antapical horns. This species is slightly larger than most small peridiniacean species here. It is distinguished by an apical pericoel, a smooth exterior, and a variable archeopyle. A case for two species based on the different types of archeopyle could be made, but otherwise the specimens appear virtually identical, and other species of dinoflagellate cysts exhibit variable archeopyle types.
Affinities/Comparison:
Alterbidinium ellentonense sp. nov. is similar to Senegalinium obscurum. However it has unequal antapical horns (as in the generic distinction), is larger, more elongate, has a longer apical horn and a more prominent apical pericoel, has no traces of tabulation other than the archeopyle and faint cingulum, and has a more eurythetaform archeopyle with frequent accessory sutures on either side of plate 4''. Other species of Alterbidiniumare usually circumcavate or cornucavate. They have different overall shapes and have species level distinctions (such as spines, granules or lineations) from Alterbidinium ellentonense sp. nov.
Previously Reported Occurrence (illustrated). Upper Paleocene, Berkeley County, South Carolina; Upper Paleocene (NP7-9), Georgia and Alabama.
Occurrence in Present Study. Paleocene, lower and upper Ellenton formations, Savannah River Site and surrounding area, South Carolina.
Alterbidinium ellentonense, Lucas-Clark, 2006, p.189–190, pl.1, figs.3–6.
Holotype: Lucas-Clark, 2006, pl.1, figs.3–4.
Age: Paleocene.
---------------------------------------------------------------------------------------------------
Original description: [Lucas-Clark, 2006]:
Diagnosis:
Medium sized pale peridinioid. Bicavate or apically cavate in the epicyst and cornucavate in the hypocyst. Distinguished by pronounced apical cavation and variable archeopyle. Ovoidal in shape with unequal antapical horns.
Archeopyle either 2a with sutures around 4'' or combination of 2a and 4''.
Tabulation shown only by archeopyle and weak folds indicating the cingulum.
Description:
Medium size, proximate peridiniacean cysts, bicavate or cornucavate in the hypocyst and apically cavate in the epicyst, with a short, wide apical horn and two short antapical horns. Left antapical horn longer and better developed than right, which is greatly reduced.
Endocyst ovoidal to pear-shaped in outline; endophragm smooth, about equal in thickness to periphragm, the two walls appressed around the archeopyle and the cingulum, and on the hypocyst except beneath horns.
Pericyst outline peridinioid, usually wider in hypocystal area; lateral margins convex; antapical margin straight to slightly convex except for horns. Periphragm thin, surface smooth or with tiny, randomly scattered granules.
Tabulation indicated by archeopyle and cingulum only.
Cingulum indicated by weak folding.
Archeopyle type variable: I+P (2a and 4'') or type I, sometimes with accessory archeopyle sutures on either side of plate 4''. Plate 2a is hexagonal, eurythetaform. If archeopyle is type I + P, the operculum is adnate along the posterior margin of 4''. If the archeopyle is type I, the operculum is free. The archeopyle appears to penetrate both cyst walls, but the exact relationship of endoarcheopyle and periarcheopyle is uncertain. Cingulum weakly indicated by folds in the periphragm. Sulcus not indicated. Accumulation bodies sometimes present.
Dimensions:
Length, 90–120 µm; width, 60–70 µm (4 specimens measured).
Remarks:
Unusual features of Alterbidinium ellentonense sp. nov. in terms of this genus include bicavation or cornucavation, rather than circumcavation. They also include a somewhat more rectangular/ovoidal shape, and only a moderate difference between the development of antapical horns. Alterbidinium ellentonense sp. nov. could be assigned to Senegalinium, except that it consistently has unequal antapical horns. This species is slightly larger than most small peridiniacean species here. It is distinguished by an apical pericoel, a smooth exterior, and a variable archeopyle. A case for two species based on the different types of archeopyle could be made, but otherwise the specimens appear virtually identical, and other species of dinoflagellate cysts exhibit variable archeopyle types.
Affinities/Comparison:
Alterbidinium ellentonense sp. nov. is similar to Senegalinium obscurum. However it has unequal antapical horns (as in the generic distinction), is larger, more elongate, has a longer apical horn and a more prominent apical pericoel, has no traces of tabulation other than the archeopyle and faint cingulum, and has a more eurythetaform archeopyle with frequent accessory sutures on either side of plate 4''. Other species of Alterbidiniumare usually circumcavate or cornucavate. They have different overall shapes and have species level distinctions (such as spines, granules or lineations) from Alterbidinium ellentonense sp. nov.
Previously Reported Occurrence (illustrated). Upper Paleocene, Berkeley County, South Carolina; Upper Paleocene (NP7-9), Georgia and Alabama.
Occurrence in Present Study. Paleocene, lower and upper Ellenton formations, Savannah River Site and surrounding area, South Carolina.