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Hystrichosphaeridium truswelliae
Hystrichosphaeridium truswelliae Wrenn and Hart, 1988
Hystrichosphaeridium tubiferum (Ehrenberg) Deflandre 1937 sensu Wilson 1967, Figure 40.
Holoype. Wrenn and Hart 1988, figs. 25.1-3
Locus typicus: Section 17, La Meseta Formation, Seymour Island, Antarctica
Stratum typicum: late early Eocene
Age: Early Eocene
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G.L. Williams short notes on species, Mesozoic-Cenozoic dinocyst course, Urbino, Italy, May 17-22, 1999 - LPP VIEWER CD-ROM 99.5.
Hystrichosphaeridium truswelliae Wrenn and Hart, 1988, is characterized by hollow processes with distally open, flared, and fenestrate process terminations. The apical processes are shorter than the others. The periphragm is smooth, the endophragm is granular. Size: endocyst diameter 39-43 µm, overall diameter 72-85 µm, process length 8-15 µm, wall thickness 2 µm.
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Original diagnosis: Wrenn and Hart 1988, p. 355: Hystrichosphaeridium truswelliae
A species of Hystrichosphaeridium characterized by hollow processes with distally open, flared, and fenestrate process terminations. Apical processes shorter than all other processes. Periphragm is smooth, whereas endophragm is granular.
Original description: Wrenn and Hart 1988, p. 355: Hystrichosphaeridium truswelliae
Shape: Subspherical to spherical skolochorate dinocysts that bear intratabular processes of various lengths. The apical processes are always the shortest; consequently, the endocyst is asymmetrically placed with respect to the imaginary shell formed by joining the process tips with a line.
Phragma: The finely granular endophragm is < 1.0 ,um thick. The smooth periphragm gives rise to infundibular intratabular processes and is closely appressed to the endophragm except beneath each process. A faint ring marks the base of most processes on the central body. The endophragm is continuous beneath the processes, hence there is no communication between the endocoel and the hollow axis of each process. The distally flared process terminations are open and highly fenestrate.
Paratabulation: The paratabulation indicated by the distribution of the processes is 4', 6", ?5c 6"', 1"", ?3s.
Paracingulum: The location of the unspiraled paracingulum is indicated by at least five intratabular processes.
Parasulcus: At least three thin infundibular parasulcal processes mark the location of the parasulcus.
Archeopyle: The apical archeopyle is formed by the partial or complete detachment of the simple apical operculum. One infundibular process arises from the center of each opercular paraplate. The operculum often falls through the archeopyle and remains within the central bodv.
Dimensions. Observed range (five specimens): diameter of endocyst, 39 to 43 Ám (mean, 41 Ám): overall diameter, 72 to 85 Ám (mean, 79 Ám); process length, 8 to 15 Ám; endophragm thickness, < 1 Ám; periphragm thickness, <1 Ám.
Discussion and Comparison with Similar Species: Wrenn and Hart 1988, p. 355
H. truswelliue is most similar to H. tubiferum (Ehrenberg, 1838) Deflandre,1937, but differs in that its periphragm is smooth and the endophragm is granular. The reverse is true m H. tubiferum. The fenestrate process terminations of H. truswelliae contrast markedly with the denticulate to serrate circular margins" (Davey and Williams, 1966b) of H. tubiferum. The fact that the operculum is commonly present, possibly adnate, may be an additional distinguishing characteristic separating H. truswelliae from other species of Hystrichosphaeridium. The process terminations of H. truswelliae are very similar to the Southem Hemisphere forms of Areosphaeridium diktyoplokus. Both have perforate distal platform or platform-like process terminations with ragged margins. These species are easily separated because H. truswelliae has hollow, distally open processes, whereas those of A. diktyoplokus are solid and distally closed. In addition, the relatively short epicystal processes characteristic of H. trustwelliae are not seen on A. dikyoplokus.
Stratigraphic Occurrence. La Meseta Formation (Section 3, late early Eocene; Sections 17 and 18, late early Eocene).
Selected Previous Occurrences. Antarctica, Ross Sea (?Eocene: Wilson 1967a).
Hystrichosphaeridium tubiferum (Ehrenberg) Deflandre 1937 sensu Wilson 1967, Figure 40.
Holoype. Wrenn and Hart 1988, figs. 25.1-3
Locus typicus: Section 17, La Meseta Formation, Seymour Island, Antarctica
Stratum typicum: late early Eocene
Age: Early Eocene
--------------------------------------------------
G.L. Williams short notes on species, Mesozoic-Cenozoic dinocyst course, Urbino, Italy, May 17-22, 1999 - LPP VIEWER CD-ROM 99.5.
Hystrichosphaeridium truswelliae Wrenn and Hart, 1988, is characterized by hollow processes with distally open, flared, and fenestrate process terminations. The apical processes are shorter than the others. The periphragm is smooth, the endophragm is granular. Size: endocyst diameter 39-43 µm, overall diameter 72-85 µm, process length 8-15 µm, wall thickness 2 µm.
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Original diagnosis: Wrenn and Hart 1988, p. 355: Hystrichosphaeridium truswelliae
A species of Hystrichosphaeridium characterized by hollow processes with distally open, flared, and fenestrate process terminations. Apical processes shorter than all other processes. Periphragm is smooth, whereas endophragm is granular.
Original description: Wrenn and Hart 1988, p. 355: Hystrichosphaeridium truswelliae
Shape: Subspherical to spherical skolochorate dinocysts that bear intratabular processes of various lengths. The apical processes are always the shortest; consequently, the endocyst is asymmetrically placed with respect to the imaginary shell formed by joining the process tips with a line.
Phragma: The finely granular endophragm is < 1.0 ,um thick. The smooth periphragm gives rise to infundibular intratabular processes and is closely appressed to the endophragm except beneath each process. A faint ring marks the base of most processes on the central body. The endophragm is continuous beneath the processes, hence there is no communication between the endocoel and the hollow axis of each process. The distally flared process terminations are open and highly fenestrate.
Paratabulation: The paratabulation indicated by the distribution of the processes is 4', 6", ?5c 6"', 1"", ?3s.
Paracingulum: The location of the unspiraled paracingulum is indicated by at least five intratabular processes.
Parasulcus: At least three thin infundibular parasulcal processes mark the location of the parasulcus.
Archeopyle: The apical archeopyle is formed by the partial or complete detachment of the simple apical operculum. One infundibular process arises from the center of each opercular paraplate. The operculum often falls through the archeopyle and remains within the central bodv.
Dimensions. Observed range (five specimens): diameter of endocyst, 39 to 43 Ám (mean, 41 Ám): overall diameter, 72 to 85 Ám (mean, 79 Ám); process length, 8 to 15 Ám; endophragm thickness, < 1 Ám; periphragm thickness, <1 Ám.
Discussion and Comparison with Similar Species: Wrenn and Hart 1988, p. 355
H. truswelliue is most similar to H. tubiferum (Ehrenberg, 1838) Deflandre,1937, but differs in that its periphragm is smooth and the endophragm is granular. The reverse is true m H. tubiferum. The fenestrate process terminations of H. truswelliae contrast markedly with the denticulate to serrate circular margins" (Davey and Williams, 1966b) of H. tubiferum. The fact that the operculum is commonly present, possibly adnate, may be an additional distinguishing characteristic separating H. truswelliae from other species of Hystrichosphaeridium. The process terminations of H. truswelliae are very similar to the Southem Hemisphere forms of Areosphaeridium diktyoplokus. Both have perforate distal platform or platform-like process terminations with ragged margins. These species are easily separated because H. truswelliae has hollow, distally open processes, whereas those of A. diktyoplokus are solid and distally closed. In addition, the relatively short epicystal processes characteristic of H. trustwelliae are not seen on A. dikyoplokus.
Stratigraphic Occurrence. La Meseta Formation (Section 3, late early Eocene; Sections 17 and 18, late early Eocene).
Selected Previous Occurrences. Antarctica, Ross Sea (?Eocene: Wilson 1967a).