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Phthanoperidinium antarcticum
Phthanoperidinium antarcticum Mao and Mohr, 1995
Holotype: Mao and Mohr, 1995, pl.I, fig.1
Locus typicus: Bruce Bank, Antarctica
Stratrum typicum: Middle Eocene (Nannoplankton-Zone CP 13b)
Isotype: Mao and Mohr, 1995, pl.I, fig.3
Diagnosis: Mao and Mohr, 1995, p. 249
Cyst proximate, small in size, spherical or subspherical to ellipsoid in shape with a small apical horn and with or without an antapical horn. Wall two-layered, closely appressed to one another except within a small horn area. Surface foveolate, superimposed with low sutural crests and parallel penitabular spines or processes, which define a tabulation of 4", 3a, 7"", Xc, 5""", 2"""". Archeopyle intercalary or combination of intercalary and precingular series, type I (2a) or I(2a) P (4"")/IPa.
Description: Mao and Mohr, 1995, p. 249, 251
Cyst quite bulgy, usually dorsoventral unflattened. Epicyst equal to or slightly longer than hypocyst. Apical horn small and short, usually 2-3 µm, up to 5 µm, in height. Antapex rounded or slightly protruded or with one small horn developed, close to the dorso-ventral meridian. Wall two-layered, periphragm closely appressed to endophragm, except for indistinct separation in small horn areas. Periphragm typically foveolate. Foveolae circular to subcircular, usually smaller than 1 µm in diameter and densely distributed, giving the surface a bubbly appearance. This character is best observed under phase contrast and is not well visible under scanning electron microscope due to the difficulty of focusing on the foveolae, which are located at a level lower than the sutural and penitabular ornaments. The sutural crests, which bear closely spaced solid and simple spines, are equal to or less in height than the penitabular spines/processes, which are simple, sinuous or branched distally and sometimes fused or connected distally. Cingulum 3-6 µm wide, almost planar or slightly spiral, delineated by low crests, and may protrude from the cyst"s outline. Sulcus delineated by low crests, slightly depressed, and broader posteriorly. Archeopyle intercalary or compound. The compound archeopyle of IP/IPa type is frequently encountered and distinct, particular the IP type. Another type of compound archeopyle 3I3P/3I3Pa, as described by Islam (1982) in the emendation of the genus Phthanoperidinium may also possibly exist, as suggested by the two separated pieces of epicyst.
Dimensions: Cyst length 33-(45)-50 µm (holotype 48 µm); cyst width 28-(40.5)-45 µm (holotype 40 µm); crest height 1-3 µm; spine/process height 2-5 µm; 30 specimens measured.
Affinities: Mao and Mohr, 1995, p. 251
Phthanoperidinium antarcticum resembles P. geminatum and P. multispinum in terms of the penitabular ornamentation, but differs in having a bubbly foveolate periphragm. P. brooksii, described in detail by Edwards and Bebout (1981), has simple parasutural crests, but has a spongy filling between endophragm and periphragm which gives this species also a slightly "bubbly" appearance.
Holotype: Mao and Mohr, 1995, pl.I, fig.1
Locus typicus: Bruce Bank, Antarctica
Stratrum typicum: Middle Eocene (Nannoplankton-Zone CP 13b)
Isotype: Mao and Mohr, 1995, pl.I, fig.3
Diagnosis: Mao and Mohr, 1995, p. 249
Cyst proximate, small in size, spherical or subspherical to ellipsoid in shape with a small apical horn and with or without an antapical horn. Wall two-layered, closely appressed to one another except within a small horn area. Surface foveolate, superimposed with low sutural crests and parallel penitabular spines or processes, which define a tabulation of 4", 3a, 7"", Xc, 5""", 2"""". Archeopyle intercalary or combination of intercalary and precingular series, type I (2a) or I(2a) P (4"")/IPa.
Description: Mao and Mohr, 1995, p. 249, 251
Cyst quite bulgy, usually dorsoventral unflattened. Epicyst equal to or slightly longer than hypocyst. Apical horn small and short, usually 2-3 µm, up to 5 µm, in height. Antapex rounded or slightly protruded or with one small horn developed, close to the dorso-ventral meridian. Wall two-layered, periphragm closely appressed to endophragm, except for indistinct separation in small horn areas. Periphragm typically foveolate. Foveolae circular to subcircular, usually smaller than 1 µm in diameter and densely distributed, giving the surface a bubbly appearance. This character is best observed under phase contrast and is not well visible under scanning electron microscope due to the difficulty of focusing on the foveolae, which are located at a level lower than the sutural and penitabular ornaments. The sutural crests, which bear closely spaced solid and simple spines, are equal to or less in height than the penitabular spines/processes, which are simple, sinuous or branched distally and sometimes fused or connected distally. Cingulum 3-6 µm wide, almost planar or slightly spiral, delineated by low crests, and may protrude from the cyst"s outline. Sulcus delineated by low crests, slightly depressed, and broader posteriorly. Archeopyle intercalary or compound. The compound archeopyle of IP/IPa type is frequently encountered and distinct, particular the IP type. Another type of compound archeopyle 3I3P/3I3Pa, as described by Islam (1982) in the emendation of the genus Phthanoperidinium may also possibly exist, as suggested by the two separated pieces of epicyst.
Dimensions: Cyst length 33-(45)-50 µm (holotype 48 µm); cyst width 28-(40.5)-45 µm (holotype 40 µm); crest height 1-3 µm; spine/process height 2-5 µm; 30 specimens measured.
Affinities: Mao and Mohr, 1995, p. 251
Phthanoperidinium antarcticum resembles P. geminatum and P. multispinum in terms of the penitabular ornamentation, but differs in having a bubbly foveolate periphragm. P. brooksii, described in detail by Edwards and Bebout (1981), has simple parasutural crests, but has a spongy filling between endophragm and periphragm which gives this species also a slightly "bubbly" appearance.