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Enneadocysta arcuata
Enneadocysta arcuata (Eaton, 1971) emend. Stover and Williams, 1995
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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.
Enneadocysta arcuata (Eaton, 1971) Stover and Williams, 1995, emend. Stover and Williams, 1995, has 18 or 19 processes, nine or 10 on the epicyst, nine on the hypocyst. Processes generally licrate distally, some simply branched. Process formula is 4', 5-6", 0c, 6"’, 2"”, 1ps. A process may or may not be present on paraplate 6", which is narrower than 1".
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Stover and Williams, 1995, p. 109
Emended description:
Shape: Cysts skolochorate with subspherical to nearly subspherical central body.
Wall relationships: Autophragm only.
Wall features: Autophragm smooth or faintly microreticulate; 18 or 19 intratabular processes present, nine or 10 on epicyst, nine on hypocyst. Process stems solid, of variable width but typically narrow, slightly fibroid and expanded distally, usually abruptly. Most process tips licrate, others simply branched. Licrate tips are arcuate to horseshoe-shaped, of moderate length with smooth inner margins and denticulate to spinulate outer margins and may be partly perforate. On precingular and postcingular processes with licrate tips, ends of arcuations directed equatorially and ends of opposing processes face each other. In general, processes on dorsal and lateral surfaces have licrate tips whereas those on ventral surface may be licrate or simply branched, frequently the latter. Ends of licrate terminations on the two antapical processes are opposite and face each other medially.
Excystment type: Archeopyle apical; operculum tetratabular, nearly equidimensional, simple and free.
Paratabulation: Expressed on epicyst by principal archeopyle and short accessory sutures, when the latter are developed, and positions of intratabular processes; indicated on hypocyst solely by positions of processes. Process formula: 4', 5-6'', 0c, 6''', 2'''', 1ps. A process may or may not be present on paraplate 6'' which is narrower than paraplate 1''. Two hypocystal processes arranged in the partiforrn pattern (text-fig. I D).
Paracingulum: Indicated by absence of processes.
Parasulcus: Limits of parasulcus indicated anteriorly by position of parasulcal notch and posteriorly by posterior sulcal process.
Size: Intermediate; measurements for 10 specimens: body diameter 38 Ám to 54 Ám, overall diameter 65 Ám to 90 Ám, process length 15 Ám to 32 Ám, most processes 20 Ám or more in length.
Comments:
The emendation of Enneadocysta arcuata takes into account the difference in width between 1'' and 6'', the orientation of the licrite tips of precingular and postcingular processes and the partiform paratabulation pattern on the hypocyst. Eaton (1971) recognized two morphotypes of this species. Specimens without a process on paraplates 6" and 6"' he designated Var. A and those with a process on paraplates 6'' and 6''' he referred to Var B. The former is more common than the latter. text-fig. 1, no. E presents both epicystal configurations.
The Southern Hemisphere species described originally as Hystrichosphaeridium dictyostilum Menendez 1965 was regarded by Cookson and Cranwell (1967) and by Eaton (1971) as a taxonomic junior synonym of the species now known as Areosphaeridium diktyoplokus. Sarjeant (1981) rejected this synonymy and reassigned Hystrichosphaeridium dictyostilum to Areosphaeridium. In the same publication he regarded Areosphaeridium arcuatum as a taxonomic junior synonym of Areosphaeridium dictyostilum. However, the processes on Areosphaeridium dictyostilum as illustrated by Menendez (1965) have reticulate vasiforrn or branched distal ends rather than the licrate process tips characteristically present on most processes of Enneadocysta arcuata. The process formula and the hypocystal paratabulation of Areosphaeridium dictyostilum are unknown. Accordingly we have transferred it provisionally to Enneadocysta.
Type locality and stratum:
Locality: southern England, Isle of Wight, Whitecliff Bay section.
Stratum: Bracklesham Beds (lower Middle Eocene, Lutetian), sample W-40 in Bed 11 of Eaton (1976), approximately 76 meters below the Bracklesham Beds - Barton Beds boundary.
Holotype:Specimen illustrated in Eaton (1971, pl. 3, fig. 1).
Stratigraphic and geographic data:
The range of Enneadocysta arcuata is early Mid Eocene (Lutetian) to Early Oligocene (Rupelian). In terms of depositional sequences, the base of Enneadocysta arcuata is in the 48.5 Ma sequence and its top is probably in the 33 Ma sequence. In terms of nannoplankton zones, the ,pecies ranges from near the top of Zone NP 14 to Zone NP 23 which, in turn, correlates with the upper part of planktonic foraminiferal Zone P 10 into Zone P 21.
Publications that depict the stratigraphic range of Enneadocysta arcuala are Williams (1977)--mid Mid
Eocene to Early Oligocene; Williams and Bujak (1977a) -- Mid Eocene to Early Oligocene; Williams and Bujak (1985)--Mid Eocene to Early Oligocene.
Occurrences:
Occurrences of Enneadocysta arcuata are confined to the Northern Hemisphere and include western Europe (England, The Netherlands, France and Germany), Norwegian Sea, Grand Banks-offshore eastern Canada, eastern U.S.A., Baja California, and China. The species has been recorded most frequently from European countries.
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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.
Enneadocysta arcuata (Eaton, 1971) Stover and Williams, 1995, emend. Stover and Williams, 1995, has 18 or 19 processes, nine or 10 on the epicyst, nine on the hypocyst. Processes generally licrate distally, some simply branched. Process formula is 4', 5-6", 0c, 6"’, 2"”, 1ps. A process may or may not be present on paraplate 6", which is narrower than 1".
--------------------------------------------------
Stover and Williams, 1995, p. 109
Emended description:
Shape: Cysts skolochorate with subspherical to nearly subspherical central body.
Wall relationships: Autophragm only.
Wall features: Autophragm smooth or faintly microreticulate; 18 or 19 intratabular processes present, nine or 10 on epicyst, nine on hypocyst. Process stems solid, of variable width but typically narrow, slightly fibroid and expanded distally, usually abruptly. Most process tips licrate, others simply branched. Licrate tips are arcuate to horseshoe-shaped, of moderate length with smooth inner margins and denticulate to spinulate outer margins and may be partly perforate. On precingular and postcingular processes with licrate tips, ends of arcuations directed equatorially and ends of opposing processes face each other. In general, processes on dorsal and lateral surfaces have licrate tips whereas those on ventral surface may be licrate or simply branched, frequently the latter. Ends of licrate terminations on the two antapical processes are opposite and face each other medially.
Excystment type: Archeopyle apical; operculum tetratabular, nearly equidimensional, simple and free.
Paratabulation: Expressed on epicyst by principal archeopyle and short accessory sutures, when the latter are developed, and positions of intratabular processes; indicated on hypocyst solely by positions of processes. Process formula: 4', 5-6'', 0c, 6''', 2'''', 1ps. A process may or may not be present on paraplate 6'' which is narrower than paraplate 1''. Two hypocystal processes arranged in the partiforrn pattern (text-fig. I D).
Paracingulum: Indicated by absence of processes.
Parasulcus: Limits of parasulcus indicated anteriorly by position of parasulcal notch and posteriorly by posterior sulcal process.
Size: Intermediate; measurements for 10 specimens: body diameter 38 Ám to 54 Ám, overall diameter 65 Ám to 90 Ám, process length 15 Ám to 32 Ám, most processes 20 Ám or more in length.
Comments:
The emendation of Enneadocysta arcuata takes into account the difference in width between 1'' and 6'', the orientation of the licrite tips of precingular and postcingular processes and the partiform paratabulation pattern on the hypocyst. Eaton (1971) recognized two morphotypes of this species. Specimens without a process on paraplates 6" and 6"' he designated Var. A and those with a process on paraplates 6'' and 6''' he referred to Var B. The former is more common than the latter. text-fig. 1, no. E presents both epicystal configurations.
The Southern Hemisphere species described originally as Hystrichosphaeridium dictyostilum Menendez 1965 was regarded by Cookson and Cranwell (1967) and by Eaton (1971) as a taxonomic junior synonym of the species now known as Areosphaeridium diktyoplokus. Sarjeant (1981) rejected this synonymy and reassigned Hystrichosphaeridium dictyostilum to Areosphaeridium. In the same publication he regarded Areosphaeridium arcuatum as a taxonomic junior synonym of Areosphaeridium dictyostilum. However, the processes on Areosphaeridium dictyostilum as illustrated by Menendez (1965) have reticulate vasiforrn or branched distal ends rather than the licrate process tips characteristically present on most processes of Enneadocysta arcuata. The process formula and the hypocystal paratabulation of Areosphaeridium dictyostilum are unknown. Accordingly we have transferred it provisionally to Enneadocysta.
Type locality and stratum:
Locality: southern England, Isle of Wight, Whitecliff Bay section.
Stratum: Bracklesham Beds (lower Middle Eocene, Lutetian), sample W-40 in Bed 11 of Eaton (1976), approximately 76 meters below the Bracklesham Beds - Barton Beds boundary.
Holotype:Specimen illustrated in Eaton (1971, pl. 3, fig. 1).
Stratigraphic and geographic data:
The range of Enneadocysta arcuata is early Mid Eocene (Lutetian) to Early Oligocene (Rupelian). In terms of depositional sequences, the base of Enneadocysta arcuata is in the 48.5 Ma sequence and its top is probably in the 33 Ma sequence. In terms of nannoplankton zones, the ,pecies ranges from near the top of Zone NP 14 to Zone NP 23 which, in turn, correlates with the upper part of planktonic foraminiferal Zone P 10 into Zone P 21.
Publications that depict the stratigraphic range of Enneadocysta arcuala are Williams (1977)--mid Mid
Eocene to Early Oligocene; Williams and Bujak (1977a) -- Mid Eocene to Early Oligocene; Williams and Bujak (1985)--Mid Eocene to Early Oligocene.
Occurrences:
Occurrences of Enneadocysta arcuata are confined to the Northern Hemisphere and include western Europe (England, The Netherlands, France and Germany), Norwegian Sea, Grand Banks-offshore eastern Canada, eastern U.S.A., Baja California, and China. The species has been recorded most frequently from European countries.
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