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Isthmocystis
From Williams et al., 2017:
[Isthmocystis, Duxbury, 1979a, p. 199-200
Type species: Isthmocystis distincta, Duxbury, 1979a (pl.1, figs.1–2; text-fig.4)]
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Original description: [Duxbury, 1979]:
Diagnosis:
Dinoflagellate cysts having a subpentagonal lateral outline and bearing a well-developed apical protrusion. The body surface is smooth to finely granular, and the epitractal to hypotractal length ratio is approximately 1:2. The epitract is devoid of any sutural ornament. Cracks, presumable along plate boundaries, may be present in the epitract when the archeopyle is only partially formed. The epitractal cingular crest is absent. The hypotract displays a reflected tabulation pattern of 6```, 1p, ?1pv, 1````, outlined by distinctive sutural crests. These crests are distally entire and commonly exhibit large perforations which transect the proximal edges of the crests but not the distal edges. The hypotractal cingular crest is well developed. The archeopyle is formed by partial or, ultimately, complete detachment of the precingular plate series.
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Modified description:
Stover and Williams 1987, p. 131:
Synopsis:
Cysts proximate, outline subpentagonal in equatorial view, subcircular in apical-antapical view; epicyst smooth to finely granular, hypocyst with parasutural crests indicating a paratabulation of 6```, 1p, 1````, ?s; archeopyle precingular, compound, types ?2P to 6P.
Description:
Shape: Subpentagonal in equatorial view, subcircular in apical-antapical view; apical protrusion may be present.
Wall relationships: Autophragm only.
Wall features: Epicyst smooth to granular, sutures may occur presumably between paraplates. Hypocyst with parasutural crests which are distally entire and may be finely to coarsely perforate proximally.
Archeopyle: Precingular, formed by the release of some or all precingular paraplates, types ?2P to 6P; operculum free.
Paratabulation: Indicated on hypocyst by parasutural crests; formula: 6```, 1p, 1````, ?s; not known for epicyst.
Paracingulum: Indicated by single transverse crest on hypocyst. Parasulcus: Not clearly indicated.
Size: Intermediate to large; diameter about 85 µm to 115 µm
Affinities:
Isthmocystis differs from Wanae Cookson and Eisenack 1958 emend. Fensome 1981 primarily in having a precingular rather than an epicystal archeopyle, and in displaying hypocystal paratabulation. Isthmocystis has a somewhat conical epicyst, whereas that on Wanaea is gently convex anteriorly. Stover and Evitt (1978, p. 223-224) indicated that paratabulation on Wanaea was expressed by parasutural features on the hypocyst. This remark was based on the undescribed species now known as Isthmocystis distincta Duxbury 1979.
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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.
Isthmocystis Duxbury, 1979a. Stover and Williams (1987, p.131) provided the following synopsis. Cysts proximate, outline subpentagonal in apical-antapical view; epicyst smooth to finely granular, hypocyst with parasutural crests indicating paratabulation of 6"' , 1p, 1"" , ?s; archeopyle precingular, compound types ?2P to 6P. This genus has a well developed cingular crest on the hypocyst, but none on the epicyst. There is usually an apical protrusion.
[Isthmocystis, Duxbury, 1979a, p. 199-200
Type species: Isthmocystis distincta, Duxbury, 1979a (pl.1, figs.1–2; text-fig.4)]
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Duxbury, 1979]:
Diagnosis:
Dinoflagellate cysts having a subpentagonal lateral outline and bearing a well-developed apical protrusion. The body surface is smooth to finely granular, and the epitractal to hypotractal length ratio is approximately 1:2. The epitract is devoid of any sutural ornament. Cracks, presumable along plate boundaries, may be present in the epitract when the archeopyle is only partially formed. The epitractal cingular crest is absent. The hypotract displays a reflected tabulation pattern of 6```, 1p, ?1pv, 1````, outlined by distinctive sutural crests. These crests are distally entire and commonly exhibit large perforations which transect the proximal edges of the crests but not the distal edges. The hypotractal cingular crest is well developed. The archeopyle is formed by partial or, ultimately, complete detachment of the precingular plate series.
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Modified description:
Stover and Williams 1987, p. 131:
Synopsis:
Cysts proximate, outline subpentagonal in equatorial view, subcircular in apical-antapical view; epicyst smooth to finely granular, hypocyst with parasutural crests indicating a paratabulation of 6```, 1p, 1````, ?s; archeopyle precingular, compound, types ?2P to 6P.
Description:
Shape: Subpentagonal in equatorial view, subcircular in apical-antapical view; apical protrusion may be present.
Wall relationships: Autophragm only.
Wall features: Epicyst smooth to granular, sutures may occur presumably between paraplates. Hypocyst with parasutural crests which are distally entire and may be finely to coarsely perforate proximally.
Archeopyle: Precingular, formed by the release of some or all precingular paraplates, types ?2P to 6P; operculum free.
Paratabulation: Indicated on hypocyst by parasutural crests; formula: 6```, 1p, 1````, ?s; not known for epicyst.
Paracingulum: Indicated by single transverse crest on hypocyst. Parasulcus: Not clearly indicated.
Size: Intermediate to large; diameter about 85 µm to 115 µm
Affinities:
Isthmocystis differs from Wanae Cookson and Eisenack 1958 emend. Fensome 1981 primarily in having a precingular rather than an epicystal archeopyle, and in displaying hypocystal paratabulation. Isthmocystis has a somewhat conical epicyst, whereas that on Wanaea is gently convex anteriorly. Stover and Evitt (1978, p. 223-224) indicated that paratabulation on Wanaea was expressed by parasutural features on the hypocyst. This remark was based on the undescribed species now known as Isthmocystis distincta Duxbury 1979.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Notes:
G.L. Williams short notes on species, Mesozoic-Cenozoic dinocyst course, Urbino, Italy, May 17-22, 1999 - LPP VIEWER CD-ROM 99.5.
Isthmocystis Duxbury, 1979a. Stover and Williams (1987, p.131) provided the following synopsis. Cysts proximate, outline subpentagonal in apical-antapical view; epicyst smooth to finely granular, hypocyst with parasutural crests indicating paratabulation of 6"' , 1p, 1"" , ?s; archeopyle precingular, compound types ?2P to 6P. This genus has a well developed cingular crest on the hypocyst, but none on the epicyst. There is usually an apical protrusion.