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Alterbidinium mcmillanii
Alterbidinium mcmillanii, Willumsen, 2012, p. 58–59, pl.1, figs.12,16–18: pl.2, figs.7–12.
Holotype: Willumsen, 2012, pl.2. figs.7–12.
Type locality: Fairfield Quarry, Dunedin, South Island, New Zealand (Figure 4). Type stratum.
Stratigraphic occurrence: Alterbidinium mcmillanii sp. nov. has its FAD c. 2.0 m below the K-Pg boundary at mid-Waipara River and its LAD in the basal Paleocene at c. 0.04m above the boundary (sample MWS-17; L22023).
Age: latest Maastrichtian–earliest Paleocene.
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Original description: [Willumsen, 2012]:
Diagnosis:
Medium-sized, circumcavate, elongated peridinoid cyst, with one apical horn and two antapical horns of unequal size. In ventral view, the left antapical horn is much reduced compared to the right antapical horn. Periphragm is covered by a baculate to echinate surface ornamentation. Endocyst is centrally located, subcircular to oval shape and covered by a dense irregular pilate to clavate surface ornamentation. The paracingulum is indicated by latterly folds of the periphragm.
Archeopyle is intercalary, type I(2a). Paratabulation is indicated by paracingulum and archeopyle only.
Description:
Intermediate, circumcavate peridinoid cyst with an elongated shape.
The pericyst bears one apical horn and two antapical horns. In ventral view the left antapical horn is much reduced compared to the right. The apical horn is 18–20 µm long, conical and terminates in a rounded tip. The right antapical horn is 20–25 µm long, pointed and has an acuminate to truncate tip.
The periphragm is c. 1 µm thick, transparent and covered by numerous evenly distributed echinae or baculae with a height of 1–2 µm. The density of spines and bacula on the periphragm differs within an assemblage recorded at the same stratigraphic level.
The endocyst is subcircular to oval in shape and located centrally and is covered by a pilate to clavate surface ornamentation (Plate 2, figures 10–12) up to 2–3 µm high in the apical and antapical parts of cyst. The endocyst is 1 µm thick and always visible.
Paracingulum is indicated by lateral projections of the periphragm and by low transverse folds (Plate 1, figure 18; Plate 2, figure 7).
The parasulcus is not indicated.
An intercalary, steno-deltaform archeopyle is always visible (Plate 1, figures 16–18). Operculum is often in place, attached along the posterior margin.
Dimensions:
Specimens measured 10, total length 77(98)108 µm; total width 55(62)70 µm.
Affinities/Discussion:
Alterbidinium mcmillanii sp. nov. differs from the type species A. aculutum (Wilson 1967) and A. papillatum (Khowaja-Ateequzzaman et al. 1991) by having surface ornamentation on both the endo- and periphragm. It differs from A. longicornutum (Roncaglia et al. 1999) by being half the size, having a less prominent apical horn and baculate ornamentation. A. pentaradiatum (Cookson and Eisenack 1965) is a much larger cyst compared to A. mcmillanii sp. nov. and also has a smooth hyaline peri-phragm. Alterbidinium mcmillanii sp. nov. differs from A. pilosum (Davey 1969) by having surface ornamentation on both the endophragm and periphragm and having no indication of a sulcus.
Holotype: Willumsen, 2012, pl.2. figs.7–12.
Type locality: Fairfield Quarry, Dunedin, South Island, New Zealand (Figure 4). Type stratum.
Stratigraphic occurrence: Alterbidinium mcmillanii sp. nov. has its FAD c. 2.0 m below the K-Pg boundary at mid-Waipara River and its LAD in the basal Paleocene at c. 0.04m above the boundary (sample MWS-17; L22023).
Age: latest Maastrichtian–earliest Paleocene.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Willumsen, 2012]:
Diagnosis:
Medium-sized, circumcavate, elongated peridinoid cyst, with one apical horn and two antapical horns of unequal size. In ventral view, the left antapical horn is much reduced compared to the right antapical horn. Periphragm is covered by a baculate to echinate surface ornamentation. Endocyst is centrally located, subcircular to oval shape and covered by a dense irregular pilate to clavate surface ornamentation. The paracingulum is indicated by latterly folds of the periphragm.
Archeopyle is intercalary, type I(2a). Paratabulation is indicated by paracingulum and archeopyle only.
Description:
Intermediate, circumcavate peridinoid cyst with an elongated shape.
The pericyst bears one apical horn and two antapical horns. In ventral view the left antapical horn is much reduced compared to the right. The apical horn is 18–20 µm long, conical and terminates in a rounded tip. The right antapical horn is 20–25 µm long, pointed and has an acuminate to truncate tip.
The periphragm is c. 1 µm thick, transparent and covered by numerous evenly distributed echinae or baculae with a height of 1–2 µm. The density of spines and bacula on the periphragm differs within an assemblage recorded at the same stratigraphic level.
The endocyst is subcircular to oval in shape and located centrally and is covered by a pilate to clavate surface ornamentation (Plate 2, figures 10–12) up to 2–3 µm high in the apical and antapical parts of cyst. The endocyst is 1 µm thick and always visible.
Paracingulum is indicated by lateral projections of the periphragm and by low transverse folds (Plate 1, figure 18; Plate 2, figure 7).
The parasulcus is not indicated.
An intercalary, steno-deltaform archeopyle is always visible (Plate 1, figures 16–18). Operculum is often in place, attached along the posterior margin.
Dimensions:
Specimens measured 10, total length 77(98)108 µm; total width 55(62)70 µm.
Affinities/Discussion:
Alterbidinium mcmillanii sp. nov. differs from the type species A. aculutum (Wilson 1967) and A. papillatum (Khowaja-Ateequzzaman et al. 1991) by having surface ornamentation on both the endo- and periphragm. It differs from A. longicornutum (Roncaglia et al. 1999) by being half the size, having a less prominent apical horn and baculate ornamentation. A. pentaradiatum (Cookson and Eisenack 1965) is a much larger cyst compared to A. mcmillanii sp. nov. and also has a smooth hyaline peri-phragm. Alterbidinium mcmillanii sp. nov. differs from A. pilosum (Davey 1969) by having surface ornamentation on both the endophragm and periphragm and having no indication of a sulcus.