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Arachnodinium antarcticum
Arachnodinium antarcticum, Wilson and Clowes, 1982
Holotype: Wilson, 1967, fig.37 (as Aiora fenestrata) and Wilson and Clowes, 1982, pl.1, figs.1-3.
Paratypes: Wilson and Clowes, 1982
Locus typicus: Minna Bluff, McMurdo Sound, Antarctica
Stratum typicum: Eocene-Oligocene
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Original description: [Wilson and Clowes, 1982, p. 100, 102]:
Diagnosis:
A species of Arachnodinium with a smooth ovoidal central body and faintly striate, locally perforate processes, finely denticulate on the upper margin. Antapical process hollow, typically broad and somewhat rectangular in cross section.
Paratabulation indicated by process distribution and pattern of trabecular network; parasutural features lacking; probable formula 4', 6", 6c, 6''', ?1p, 1''', Xs.
Description:
The periphragm is thin and irregularly perforate on the ribbon-like trabecular network (perforation diameter up to 7 µm). The endophragm is smooth, relatively thin and closely attached to the periphragm of the central body. The broadly oval central body has a polygonal upper margin delimiting a probable tetratabular apical archeopyle - no specimens were seen with an operculum in position although one specimen was observed with an apparent displaced, simple, cap-shaped operculum ([Wilson and Clowes, 1982] Plate 1, figures 7-9). Seven ribbon-like processes - three broad and flattened, four somewhat more filamentous - radiate in a lateral plane from the central body immediately below the archeopyle. At a distance of about 2011m from the central body the processes are reflexed towards the antapex where they bifurcate; diverging elements from adjacent processes then coalesce, somewhat variably, to form a completely encircling, widely spaced network around the entire central body. The uppermost margins of the processes are typically denticulate ([Wilson and Clowes, 1982] Plate 1, figure 4; Plate 2, figures 7-9). The seven radial processes appear to be intratabular and are considered to represent six precingular paraplates plus one sulcul paraplate. The large antapical process, formed by an expansion of the periphragm, is membranous, smooth, hollow, closed distally and is not in communication with the other processes or with the endocoel ([Wilson and Clowes, 1982] Plate 1, figures 2, 5, 12); it is considered to represent a single antapical paraplate. The presence of six paracingular, six postcingular and a single posterior intercalary paraplate is suggested by the number and distribution of polygonal fields formed by the trabecular network ([Wilson and Clowes,1982] Text-Figure 2). No indications of a paracingulum or parasulcus are present on the central body, the greater part of which is devoid of ornament.
Dimensions:
Holotype: overall length (excluding operculum) 105 µm, breadth 96 µm, length of central body (excluding operculum) 58 µm, breadth of central body 48 µm, length of antapical process (slightly folded) 22 µm.
Range of 14 specimens: overall length (excluding operculum) 83(96)107 µm, breadth 73(98)129 µm, length of central body (excluding operculum) 44(53)69 µm, breadth of central body 33(42)50 µm, length of antapical process 22(32)50 µm.
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Notes:
G.L. Williams short notes on species, Mesozoic-Cenozoic dinocyst course, Urbino, Italy, May 17-22, 1999 - LPP VIEWER CD-ROM 99.5.
Arachnodinium antarcticum Wilson and Clowes, 1982. According to Wilson and Clowes (1982, p.100) has a smooth ovoidal central body and faintly striate, locally perforate processes, finely denticulate on the upper margin. Antapical process is hollow, typically broad and somewhat rectangular in cross section. Paratabulation indicated by process distribution and pattern of trabecular network; parasutural features lacking; probable formula 4', 6", 6c, 6"’, ?1p, 1"”, xs. Arachnodinium antarcticum differs from Flamingoia cometa in having 7 epicystal and 1 hypocystal processes rather than 6 epicystal and 2 hypocystal processes. The precingular processes in F.cometa are more centrally located on the plates. F.cometa also may have a 1p process. The antapical process in A.antarcticum is closed, hollow, bulbous and not connected to the equatorial trabeculum. The antapical process in F. cometa is large, elongate, hollow, open and coalesces with the post antapical trabeculum.
Size: length (excluding operculum) 83-107 µm, width 73-129 µm, central body length 44-69 µm, width 33-50 µm. Antapical process length 22-50 µm.
Holotype: Wilson, 1967, fig.37 (as Aiora fenestrata) and Wilson and Clowes, 1982, pl.1, figs.1-3.
Paratypes: Wilson and Clowes, 1982
Locus typicus: Minna Bluff, McMurdo Sound, Antarctica
Stratum typicum: Eocene-Oligocene
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Wilson and Clowes, 1982, p. 100, 102]:
Diagnosis:
A species of Arachnodinium with a smooth ovoidal central body and faintly striate, locally perforate processes, finely denticulate on the upper margin. Antapical process hollow, typically broad and somewhat rectangular in cross section.
Paratabulation indicated by process distribution and pattern of trabecular network; parasutural features lacking; probable formula 4', 6", 6c, 6''', ?1p, 1''', Xs.
Description:
The periphragm is thin and irregularly perforate on the ribbon-like trabecular network (perforation diameter up to 7 µm). The endophragm is smooth, relatively thin and closely attached to the periphragm of the central body. The broadly oval central body has a polygonal upper margin delimiting a probable tetratabular apical archeopyle - no specimens were seen with an operculum in position although one specimen was observed with an apparent displaced, simple, cap-shaped operculum ([Wilson and Clowes, 1982] Plate 1, figures 7-9). Seven ribbon-like processes - three broad and flattened, four somewhat more filamentous - radiate in a lateral plane from the central body immediately below the archeopyle. At a distance of about 2011m from the central body the processes are reflexed towards the antapex where they bifurcate; diverging elements from adjacent processes then coalesce, somewhat variably, to form a completely encircling, widely spaced network around the entire central body. The uppermost margins of the processes are typically denticulate ([Wilson and Clowes, 1982] Plate 1, figure 4; Plate 2, figures 7-9). The seven radial processes appear to be intratabular and are considered to represent six precingular paraplates plus one sulcul paraplate. The large antapical process, formed by an expansion of the periphragm, is membranous, smooth, hollow, closed distally and is not in communication with the other processes or with the endocoel ([Wilson and Clowes, 1982] Plate 1, figures 2, 5, 12); it is considered to represent a single antapical paraplate. The presence of six paracingular, six postcingular and a single posterior intercalary paraplate is suggested by the number and distribution of polygonal fields formed by the trabecular network ([Wilson and Clowes,1982] Text-Figure 2). No indications of a paracingulum or parasulcus are present on the central body, the greater part of which is devoid of ornament.
Dimensions:
Holotype: overall length (excluding operculum) 105 µm, breadth 96 µm, length of central body (excluding operculum) 58 µm, breadth of central body 48 µm, length of antapical process (slightly folded) 22 µm.
Range of 14 specimens: overall length (excluding operculum) 83(96)107 µm, breadth 73(98)129 µm, length of central body (excluding operculum) 44(53)69 µm, breadth of central body 33(42)50 µm, length of antapical process 22(32)50 µm.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Notes:
G.L. Williams short notes on species, Mesozoic-Cenozoic dinocyst course, Urbino, Italy, May 17-22, 1999 - LPP VIEWER CD-ROM 99.5.
Arachnodinium antarcticum Wilson and Clowes, 1982. According to Wilson and Clowes (1982, p.100) has a smooth ovoidal central body and faintly striate, locally perforate processes, finely denticulate on the upper margin. Antapical process is hollow, typically broad and somewhat rectangular in cross section. Paratabulation indicated by process distribution and pattern of trabecular network; parasutural features lacking; probable formula 4', 6", 6c, 6"’, ?1p, 1"”, xs. Arachnodinium antarcticum differs from Flamingoia cometa in having 7 epicystal and 1 hypocystal processes rather than 6 epicystal and 2 hypocystal processes. The precingular processes in F.cometa are more centrally located on the plates. F.cometa also may have a 1p process. The antapical process in A.antarcticum is closed, hollow, bulbous and not connected to the equatorial trabeculum. The antapical process in F. cometa is large, elongate, hollow, open and coalesces with the post antapical trabeculum.
Size: length (excluding operculum) 83-107 µm, width 73-129 µm, central body length 44-69 µm, width 33-50 µm. Antapical process length 22-50 µm.