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Eatonicysta sequestra
Eatonicysta sequestra Stover and Williams, 1995
Holotype: Stover and Williams 1995: Plate 2, Figures la-d.
Locus typicus: southern England, Isle of Wight, Whitecliff Bay section.
Stratum typicum: Bracklesham Beds (lower Middle Eocene. Lutetian), Bed 10a in Eaton (1976).
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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.
Eatonicysta sequestra Stover and Williams, 1995. According to Stover and Williams (1995, p.105), this species has an incomplete ectophragm. There are up to 23 processes, 10 on the epicyst, seven on the hypocyst, and six paracingular processes. Some large processes have two or three stems. Processes expanded distally and support an incomplete ectophragm with smooth, thin trabeculae, and with irregularly perforated to reticulate areas composed of small to large openings. Process stems mostly narrow, hollow to partly or completely solid, partly or wholly fibroid, about equal in length, expanded more distally, and may be fenestrate. Outlines of the perforated ectophragmal areas at the distal ends of the processes are irregular to evenly polygonal (clypeate); the latter simulate the shapes of the paraplates. Process formula ?4', 6", 6c, 5"’, 1p, 1"”.. E.sequestra differs from E.ursulae in having a less complete ectophragm, with some distinct perforated areas similar to the clypeate terminations on the processes of Enneadocysta fenestrata and some specimens of Areosphaeridium diktyoplokum and by having a few processes with more than one stem. It differs from all three species in having six paracingular processes. Size: Holotype, central body width 58 µm, length, no operculum, 54 µm, overall width 119 µm, process length 24-28 µm, process width about 1.5-4 µm, most processes less than 3 µm wide at midlength.
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Original description: Stover and Williams 1995, p. 105
Shape: Cysts holocavate, with subspherical central bodies.
Wall relationships: Autophragm complete, ectophragm incomplete reticulum and trabeculae supported by processes.
Wall features: Autophragm smooth and bears up to 23 processes, 10 on epicyst, seven on hypocyst and six paracingular processes. Basically one process per paraplate but some large processes have two or three stems. Processes expanded distally and support an incomplete ectophragm with smooth, thin trabeculae. and with
irregularly perforated to reticulate areas composed of small to large openings. Process stems mostly narrow, hollow to partly or completely solid, partly or wholly fibroid, approximately equal in length, expanded slightly proximally, more so distally: expanded parts may be finely fenestrate. Outlines of the perforated ectophragmal areas at the distal ends of the processes are irregular to evenly polygonal (clypeate); the latter simulate the shapes of the paraplates.
Excystment mode: Archeopyle apical; however, isolated opercula have not been observed.
Paratabulation: Sexiform gonyaulacoid, expressed on epicyst by principal and accessory archeopyle sutures and by locations of intratabular processes, elsewhere on the cyst solely by the positions of the processes. Process formula: ?4'. 6", 6c. 5"', 1p, 1"".
Paracingulum: Indicated by the presence of six paracingular processes; processes typically very narrow and may be perforated distally
Parasulcus: Indicated by the absence of processes.
Size: Large; measurements of holotype: central body width 58Ám, body length (no operculum) 54Ám, overall width 119Ám, process length 24Ám to 28Ám, process width about 1.5Ám to 4Ám, most processes less than 3Ám wide at midlength.
Comparison: Stover and Williams 1995, p. 105
Eatonicysta sequestra differs from Eatonicysta ursulae in having a less complete ectophragm (pl. 2, figs. la, d) with some distinct, perforated areas resembling the clypeate terminations on the processes of Enneadocysta fenestrata and some specimens of Areosphaeridium diktyoplokus and by having a few processes with more than one stem (pl. 2, fig. I c). In addition, Eatonicysta sequestra has paracingular processes (text-fig. 1, no. D) which are absent on most specimens of Eatonicysta ursulae (text-fig. 1, nos. B I -B2).
Heilmann-Clausen (1993) described and illustrated time-related morphologic changes in Eatonicysta ursulae. The samples studied ranged from 56 to 55 Ma [using the time scale of Aubry et al. (1988)] and were from Denmark and Germany. The oldest specimens, assignable to Eatonicysta furensis stat. nov. (as Eatonicysta
ursulae subsp. furensis) have short open processes that are developed distally into perforate membranes. Adjacent processes distally are not joined or are united by a few trabeculae. Within less than 500,000 years appeared morphotypes, which Heilmann-Clausen (1993, text-fig. 4, pl. 1. figs. 4-6), considered to be Eatonicysta ursulae but which may be Eatonicysta sequestra. Unfortunately, it is not possible to tell if the specimens illustrated by Heilmann-Clausen have paracingular processes. The first specimens of Eatonicysta ursulae with development of a continuous ectophragmal network occur in a higher sample. about 500,000 years younger.
Stratigraphic and geographic data: Stover and Williams 1995, p. 105
The age in southern England is Early Mid Eocene (Lutetian), local palynological zone B-3 (Eaton 1976). The species has been recorded from southern England. Hampshire Basin, Bracklesham Beds in the 48.5 Ma depositional sequence. The specimens identified as Eatonicysta ursulae by Heilmann- Clausen (1993) are from the Ypresian Rosnaes Clay of Denmark. This would extend the base to 53.5 Ma [using the time scale of Haq et al. (1987)].
Holotype: Stover and Williams 1995: Plate 2, Figures la-d.
Locus typicus: southern England, Isle of Wight, Whitecliff Bay section.
Stratum typicum: Bracklesham Beds (lower Middle Eocene. Lutetian), Bed 10a in Eaton (1976).
--------------------------------------------------
G.L. Williams short notes on species, Mesozoic-Cenozoic dinocyst course, Urbino, Italy, May 17-22, 1999 - LPP VIEWER CD-ROM 99.5.
Eatonicysta sequestra Stover and Williams, 1995. According to Stover and Williams (1995, p.105), this species has an incomplete ectophragm. There are up to 23 processes, 10 on the epicyst, seven on the hypocyst, and six paracingular processes. Some large processes have two or three stems. Processes expanded distally and support an incomplete ectophragm with smooth, thin trabeculae, and with irregularly perforated to reticulate areas composed of small to large openings. Process stems mostly narrow, hollow to partly or completely solid, partly or wholly fibroid, about equal in length, expanded more distally, and may be fenestrate. Outlines of the perforated ectophragmal areas at the distal ends of the processes are irregular to evenly polygonal (clypeate); the latter simulate the shapes of the paraplates. Process formula ?4', 6", 6c, 5"’, 1p, 1"”.. E.sequestra differs from E.ursulae in having a less complete ectophragm, with some distinct perforated areas similar to the clypeate terminations on the processes of Enneadocysta fenestrata and some specimens of Areosphaeridium diktyoplokum and by having a few processes with more than one stem. It differs from all three species in having six paracingular processes. Size: Holotype, central body width 58 µm, length, no operculum, 54 µm, overall width 119 µm, process length 24-28 µm, process width about 1.5-4 µm, most processes less than 3 µm wide at midlength.
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Original description: Stover and Williams 1995, p. 105
Shape: Cysts holocavate, with subspherical central bodies.
Wall relationships: Autophragm complete, ectophragm incomplete reticulum and trabeculae supported by processes.
Wall features: Autophragm smooth and bears up to 23 processes, 10 on epicyst, seven on hypocyst and six paracingular processes. Basically one process per paraplate but some large processes have two or three stems. Processes expanded distally and support an incomplete ectophragm with smooth, thin trabeculae. and with
irregularly perforated to reticulate areas composed of small to large openings. Process stems mostly narrow, hollow to partly or completely solid, partly or wholly fibroid, approximately equal in length, expanded slightly proximally, more so distally: expanded parts may be finely fenestrate. Outlines of the perforated ectophragmal areas at the distal ends of the processes are irregular to evenly polygonal (clypeate); the latter simulate the shapes of the paraplates.
Excystment mode: Archeopyle apical; however, isolated opercula have not been observed.
Paratabulation: Sexiform gonyaulacoid, expressed on epicyst by principal and accessory archeopyle sutures and by locations of intratabular processes, elsewhere on the cyst solely by the positions of the processes. Process formula: ?4'. 6", 6c. 5"', 1p, 1"".
Paracingulum: Indicated by the presence of six paracingular processes; processes typically very narrow and may be perforated distally
Parasulcus: Indicated by the absence of processes.
Size: Large; measurements of holotype: central body width 58Ám, body length (no operculum) 54Ám, overall width 119Ám, process length 24Ám to 28Ám, process width about 1.5Ám to 4Ám, most processes less than 3Ám wide at midlength.
Comparison: Stover and Williams 1995, p. 105
Eatonicysta sequestra differs from Eatonicysta ursulae in having a less complete ectophragm (pl. 2, figs. la, d) with some distinct, perforated areas resembling the clypeate terminations on the processes of Enneadocysta fenestrata and some specimens of Areosphaeridium diktyoplokus and by having a few processes with more than one stem (pl. 2, fig. I c). In addition, Eatonicysta sequestra has paracingular processes (text-fig. 1, no. D) which are absent on most specimens of Eatonicysta ursulae (text-fig. 1, nos. B I -B2).
Heilmann-Clausen (1993) described and illustrated time-related morphologic changes in Eatonicysta ursulae. The samples studied ranged from 56 to 55 Ma [using the time scale of Aubry et al. (1988)] and were from Denmark and Germany. The oldest specimens, assignable to Eatonicysta furensis stat. nov. (as Eatonicysta
ursulae subsp. furensis) have short open processes that are developed distally into perforate membranes. Adjacent processes distally are not joined or are united by a few trabeculae. Within less than 500,000 years appeared morphotypes, which Heilmann-Clausen (1993, text-fig. 4, pl. 1. figs. 4-6), considered to be Eatonicysta ursulae but which may be Eatonicysta sequestra. Unfortunately, it is not possible to tell if the specimens illustrated by Heilmann-Clausen have paracingular processes. The first specimens of Eatonicysta ursulae with development of a continuous ectophragmal network occur in a higher sample. about 500,000 years younger.
Stratigraphic and geographic data: Stover and Williams 1995, p. 105
The age in southern England is Early Mid Eocene (Lutetian), local palynological zone B-3 (Eaton 1976). The species has been recorded from southern England. Hampshire Basin, Bracklesham Beds in the 48.5 Ma depositional sequence. The specimens identified as Eatonicysta ursulae by Heilmann- Clausen (1993) are from the Ypresian Rosnaes Clay of Denmark. This would extend the base to 53.5 Ma [using the time scale of Haq et al. (1987)].