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Hemicystodinium sp. 2 of chateauneuf 1980
Hemicystodinium sp. 2 of Chateauneuf, 1980
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Genus: Genus: Hemicystodinium Wall, 1967
tax. jr. synonym of Polysphaeridium Davey and Williams, 1966, according to Bujak et al., 1980
Type species: Hemicystodinium zoharyi (Rossignol, 1964); Wall, 1967
Original description: Wall, 1967, p. 110
Spherical to ovoid dinoflagellate cysts which dehisce equatorially to form hemispheres; rims of the hemispheres with a small projection or indentation and slight displacement at the midventral point. Ornamentation variable, from microreticulate to spinose; spines, when present, variable in length and predominantly simple. Elements of ornamentation randomly disposed or intratabular.
Supplemental description: Wall and Dale, 1969, p. 143
Wall and Dale (1969) were the first to describe the archeopyle formation in detail. Although their description includes a concise account of each stage of development, only that part pertaining to archeopyle formation in the cyst is presented below:
Cysts rupture to form a combination Type 2A + 6P archeopyle. The epitract of the cyst separates by a suture from the hypotract and the cingular area. The epitract itself is divided by sutures into 8 opercular pieces whose shape and mutual configuration correspond very precisely with the arrangement of the epithecal plates of the theca. They include the plate equivalents of 6 precingular plates, the first apical plate and a single opercular piece which represents the plate equivalents of 2", 3", 4" and the apical closing plate. A prominent notch in the epitract and a corresponding projection on the midventral part of the hypotract are developed; this projection is the plate equivalent of the anterior sulcal platelet of the theca.
Stover and Evitt, 1978, p. 208-209
Synopsis: Cysts skolochorate, acavate; body subspherical with numerous nontabular processes; paratabulation gonyaulacacean, indicated on epicyst only by opercular pieces of combination archeopyle, Type A+3A+6P.
Modified description:
Shape: Body subspherical; isolated hypocysts commonly seen in apical-antapical orientation.
Wall relationships: Cysts acavate; endophragm and periphragm appressed between processes.
Wall features: No parasutural features on hypocyst; on epicyst, opercular pieces separate along paraplate boundaries. Processes typically hollow; may be short relative to body size, with few to several processes per paraplate. Periphragm between processes scabrate or punctoreticulate.
Paratabulation: Indicated on epicyst by archeopyle sutures and opercular pieces; not indicated on hypocyst.
Archeopyle: Combination archeopyle, Type A+3A+6P; principal archeopyle suture straight along apical margin of paracingulum except at midventral surface, where it follows the outline of the parasulcal tab and the shalapical margin of paracilow depression on its right side. Parasulcal tab corresponds to high position of anteriorsulcal paraplate; the depression corresponds to low position of paraplate 6". Six precingular and first apical paraplates separate individually; apical paraplates 2"-4" remain together, although separated from the other seven opercular pieces; operculum free.
Paracingulum: Position indicated by archeopyle margin and by transverse alignment of processes.
Parasulcus: Apical limit indicated by parasulcal tab.
Size: Small to intermediate.
Affinities:
Stover and Evitt, 1978, p. 209: Hemicystodinium differs from Eocladopyxis in that its hypocyst lacks parasutural features and does not separate into its constituent paraplates. Homotryblium, which also has a combination Type A+"3A"+6P archeopyle, has intratabular processes rather than nontabular processes.
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Genus: Genus: Hemicystodinium Wall, 1967
tax. jr. synonym of Polysphaeridium Davey and Williams, 1966, according to Bujak et al., 1980
Type species: Hemicystodinium zoharyi (Rossignol, 1964); Wall, 1967
Original description: Wall, 1967, p. 110
Spherical to ovoid dinoflagellate cysts which dehisce equatorially to form hemispheres; rims of the hemispheres with a small projection or indentation and slight displacement at the midventral point. Ornamentation variable, from microreticulate to spinose; spines, when present, variable in length and predominantly simple. Elements of ornamentation randomly disposed or intratabular.
Supplemental description: Wall and Dale, 1969, p. 143
Wall and Dale (1969) were the first to describe the archeopyle formation in detail. Although their description includes a concise account of each stage of development, only that part pertaining to archeopyle formation in the cyst is presented below:
Cysts rupture to form a combination Type 2A + 6P archeopyle. The epitract of the cyst separates by a suture from the hypotract and the cingular area. The epitract itself is divided by sutures into 8 opercular pieces whose shape and mutual configuration correspond very precisely with the arrangement of the epithecal plates of the theca. They include the plate equivalents of 6 precingular plates, the first apical plate and a single opercular piece which represents the plate equivalents of 2", 3", 4" and the apical closing plate. A prominent notch in the epitract and a corresponding projection on the midventral part of the hypotract are developed; this projection is the plate equivalent of the anterior sulcal platelet of the theca.
Stover and Evitt, 1978, p. 208-209
Synopsis: Cysts skolochorate, acavate; body subspherical with numerous nontabular processes; paratabulation gonyaulacacean, indicated on epicyst only by opercular pieces of combination archeopyle, Type A+3A+6P.
Modified description:
Shape: Body subspherical; isolated hypocysts commonly seen in apical-antapical orientation.
Wall relationships: Cysts acavate; endophragm and periphragm appressed between processes.
Wall features: No parasutural features on hypocyst; on epicyst, opercular pieces separate along paraplate boundaries. Processes typically hollow; may be short relative to body size, with few to several processes per paraplate. Periphragm between processes scabrate or punctoreticulate.
Paratabulation: Indicated on epicyst by archeopyle sutures and opercular pieces; not indicated on hypocyst.
Archeopyle: Combination archeopyle, Type A+3A+6P; principal archeopyle suture straight along apical margin of paracingulum except at midventral surface, where it follows the outline of the parasulcal tab and the shalapical margin of paracilow depression on its right side. Parasulcal tab corresponds to high position of anteriorsulcal paraplate; the depression corresponds to low position of paraplate 6". Six precingular and first apical paraplates separate individually; apical paraplates 2"-4" remain together, although separated from the other seven opercular pieces; operculum free.
Paracingulum: Position indicated by archeopyle margin and by transverse alignment of processes.
Parasulcus: Apical limit indicated by parasulcal tab.
Size: Small to intermediate.
Affinities:
Stover and Evitt, 1978, p. 209: Hemicystodinium differs from Eocladopyxis in that its hypocyst lacks parasutural features and does not separate into its constituent paraplates. Homotryblium, which also has a combination Type A+"3A"+6P archeopyle, has intratabular processes rather than nontabular processes.