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Phthanoperidinium brooksii
Phthanoperidinium brooksii Edwards and Bebout, 1981
Holotype: Edwards and Bebout, 1981, pl.1, fig.1-3
Locus typicus: 38¦ 46" 20"" N latitude, 72¦ 48" 20"" W longitude, Atlantic
Stratum typicum: Middle-late Eocene
Original diagnosis: Edwards and Bebout, 1981, p. 38
A species of Phthanoperidinium bearing filmy parasutural features with poorly delimited crests of variable height, a broadly spatulate 1" paraplate, and a strongly offset paracingulum. Scanning electron microscope studies reveal the indefiniteness of the parasutural crests to be the result of a layer of cancellous material, which grades laterally into both endophragm and periphragm and which completely fills the space between these layers. The archeopyle is intercalary, typically Type I, but may be 2I, 3I, or I + P.
Original description: Edwards and Bebout, 1981, p. 38-39
Shape: Ellipsoidal, but not strongly so; length to width ratio typically within the range 1.1:1 to 1.3:1; apical horn present, 1 or 2 antapical horns usually present, variably well developed.
Wall relationships: Endophragm and periphragm thin, separated by a cancellous filling that grades into both wall layers.
Wall features: Periphragm with parasutural ridges 1-5 µm high, generally having irregular margins; exterior of the endophragm grades into the cancellous filling which, in turn, grades into the interior of the periphragm (see Text-Figure 2); periphragm exterior dotted with pustules which suggest penitabular ornamentation in a few places; interior of the endophragm smooth.
Paratabulation: Expressed by parasutural crests; paratabulation formula is 4", 3a, 7"", Xc, 5""", 2"""", Xs (Text-Figure 3).
Archeopyle: All include at least one intercalary paraplate, typically formed by the loss of the 2a paraplate alone, and in a few by the additional loss of either the la or 3a paraplates, rarely by the loss of all three intercalaries or by the loss of the 2a and 4"; additional cracks (accessory sutures?) may be present.
Paracingulum: Strongly helicoid, offset by one paracingular width or more; only a few weak indications of individual cingular paraplates.
Parasulcus: Prominent, extends from posterior margin of paraplate 1" to antapex; little or no indication of subdivision into sulcal paraplates.
Size: Holotype 50 x 43 µm; size range: length 41-56 µm (46 µm average), width 32-46 µm (40 µm average). Other features: The shape of the first apical paraplate and its relationship to the paraplates in the precingular series serve to distinguish P. brooksii from other published species of Phthanoperidinium. Paraplate 1" is broadly spatulate and is in broad contact with paraplate 6". This distinctive feature, previously unreported in the fossil record, is illustrated in Text-Figure 4.
Affinities:
Edwards and Bebout, 1981, p. 39: An examination of Table I shows that several of the previously published species of Phthanoperidinium are similar to P. brooksii in that they have parasutural crests that lack spines, hairlike projections, or branched appendages. These species include P. amoenum, P. crenulatum, P. eocenicum,P. geminatum, P. levimurum, and P. schizokeras. Nonetheless, these species may be distinguished from P. brooksii by the following criteria: P. amoenum has parasutural crests which are clearly denticulate, and therefore have a beaded appearance; P. geminatum has a prominent geminate ornamentation; and P. crenulatum, P. eocenicum, P. levimurum, and P. schizokeras all have smooth, transparent, lightly or prominently denticulate parasutural crests which are totally unlike the indefinite, irregular parasutural crests of P. brooksii. Perhaps most distinctive of all is the fact that none of these species possess the distinctive, spatulate-shaped 1" paraplate of P. brooksii.
Holotype: Edwards and Bebout, 1981, pl.1, fig.1-3
Locus typicus: 38¦ 46" 20"" N latitude, 72¦ 48" 20"" W longitude, Atlantic
Stratum typicum: Middle-late Eocene
Original diagnosis: Edwards and Bebout, 1981, p. 38
A species of Phthanoperidinium bearing filmy parasutural features with poorly delimited crests of variable height, a broadly spatulate 1" paraplate, and a strongly offset paracingulum. Scanning electron microscope studies reveal the indefiniteness of the parasutural crests to be the result of a layer of cancellous material, which grades laterally into both endophragm and periphragm and which completely fills the space between these layers. The archeopyle is intercalary, typically Type I, but may be 2I, 3I, or I + P.
Original description: Edwards and Bebout, 1981, p. 38-39
Shape: Ellipsoidal, but not strongly so; length to width ratio typically within the range 1.1:1 to 1.3:1; apical horn present, 1 or 2 antapical horns usually present, variably well developed.
Wall relationships: Endophragm and periphragm thin, separated by a cancellous filling that grades into both wall layers.
Wall features: Periphragm with parasutural ridges 1-5 µm high, generally having irregular margins; exterior of the endophragm grades into the cancellous filling which, in turn, grades into the interior of the periphragm (see Text-Figure 2); periphragm exterior dotted with pustules which suggest penitabular ornamentation in a few places; interior of the endophragm smooth.
Paratabulation: Expressed by parasutural crests; paratabulation formula is 4", 3a, 7"", Xc, 5""", 2"""", Xs (Text-Figure 3).
Archeopyle: All include at least one intercalary paraplate, typically formed by the loss of the 2a paraplate alone, and in a few by the additional loss of either the la or 3a paraplates, rarely by the loss of all three intercalaries or by the loss of the 2a and 4"; additional cracks (accessory sutures?) may be present.
Paracingulum: Strongly helicoid, offset by one paracingular width or more; only a few weak indications of individual cingular paraplates.
Parasulcus: Prominent, extends from posterior margin of paraplate 1" to antapex; little or no indication of subdivision into sulcal paraplates.
Size: Holotype 50 x 43 µm; size range: length 41-56 µm (46 µm average), width 32-46 µm (40 µm average). Other features: The shape of the first apical paraplate and its relationship to the paraplates in the precingular series serve to distinguish P. brooksii from other published species of Phthanoperidinium. Paraplate 1" is broadly spatulate and is in broad contact with paraplate 6". This distinctive feature, previously unreported in the fossil record, is illustrated in Text-Figure 4.
Affinities:
Edwards and Bebout, 1981, p. 39: An examination of Table I shows that several of the previously published species of Phthanoperidinium are similar to P. brooksii in that they have parasutural crests that lack spines, hairlike projections, or branched appendages. These species include P. amoenum, P. crenulatum, P. eocenicum,P. geminatum, P. levimurum, and P. schizokeras. Nonetheless, these species may be distinguished from P. brooksii by the following criteria: P. amoenum has parasutural crests which are clearly denticulate, and therefore have a beaded appearance; P. geminatum has a prominent geminate ornamentation; and P. crenulatum, P. eocenicum, P. levimurum, and P. schizokeras all have smooth, transparent, lightly or prominently denticulate parasutural crests which are totally unlike the indefinite, irregular parasutural crests of P. brooksii. Perhaps most distinctive of all is the fact that none of these species possess the distinctive, spatulate-shaped 1" paraplate of P. brooksii.