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Corculodinium uniconicum
Corculodinium uniconicum, Batten and Lister, 1988
Holotype: Batten and Lister, 1988, figs.3h,i
Locus typicus: Shepherd's Chine Member of the Vectis Formation, Isle of Wight
Stratum typicum: Barremian
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Original diagnosis: [Batten and Lister, 1988, p.350-351]:
Diagnosis:
Diminutive two-layered cyst, typically heart-shaped in outline maximum diameter 23(26)30 x 23(26)35 µm (20 specimens). Epicyst broader than hypocyst, slightly to moderately bulging outwards from median paracingular zone and incurving to form a very shallow median depression at apex in undehisced specimens. Hypocyst usually slightly longer than epicyst, typically conical in shape, rounded or pointed at antapex. Periphragm very thin (0.5 µm or less), laevigate, closely to moderately adpressed to endocyst, not always discernible and not developed on some specimens; otherwise indicated by crumpling and occasionally by a minute pericoel at tip of antapex. Endophragm thin (c. 1 µm), uniformly sculptured with densely distributed, minute granules. Granulation more distinct where periphragm is either closely adpressed to endophragm or incompletely developed, fairly to very subdued in cysts with well-developed periphragms.
Paratabulation either not detectable or partly indicated by archeopyle development and sometimes by creases corresponding approximately to paracingular and some parasutural boundaries.
Archeopyle often undeveloped but when present appears to be a combination apical/ intercalary type, formed by opening of a ventrally adnate simple operculum fitting into a shallow depression at apex. It is sometimes slightly enlarged by secondary splitting along variably developed accessory sutures in aperture margin which delimit a number of precingular paraplates. Margin of archeopyle moderately curved in precingular series. Operculum appears to have an angular outer edge but configuration of paraplates is indeterminate.
Parasulcus occasionally indicated by longitudinal creases on ventral surface.
Paratabulation tentatively interpreted as peridiniacean; suggested formula, ?1-4", ?1 3a, 7", 0c, 5""", 2"""".
Remarks:
A small accumulation body in the mid-ventral area was noted in several cysts. Two basic morphotypes of this species were recognized. The forms that exhibit a distinctly granulate surface sculpture are generally more rounded with a less acuminate hypocystal cone, and appear to lack a pericyst, although rarely they may show incipient development of an ectophragm. By contrast, those with a laevigate periphragm, which is indicated by wrinkling and occasionally by a slight separation from the endocyst at the antapex, usually have a weakly sculptured endocyst, and commonly a more angular heart-shaped outline and a pointed antapex. The combination of characters is this second morphotype indicates more clearly the peridiniacean affinity of the species; indeed, a few of the specimens encountered display a tendency towards a "deflandreoid" appearance with a slight leftward shift of the hypocystal cone, and in one the tip of the antapex is also very slightly offset to the left in the manner of a small antapical horn.
Holotype: Batten and Lister, 1988, figs.3h,i
Locus typicus: Shepherd's Chine Member of the Vectis Formation, Isle of Wight
Stratum typicum: Barremian
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Original diagnosis: [Batten and Lister, 1988, p.350-351]:
Diagnosis:
Diminutive two-layered cyst, typically heart-shaped in outline maximum diameter 23(26)30 x 23(26)35 µm (20 specimens). Epicyst broader than hypocyst, slightly to moderately bulging outwards from median paracingular zone and incurving to form a very shallow median depression at apex in undehisced specimens. Hypocyst usually slightly longer than epicyst, typically conical in shape, rounded or pointed at antapex. Periphragm very thin (0.5 µm or less), laevigate, closely to moderately adpressed to endocyst, not always discernible and not developed on some specimens; otherwise indicated by crumpling and occasionally by a minute pericoel at tip of antapex. Endophragm thin (c. 1 µm), uniformly sculptured with densely distributed, minute granules. Granulation more distinct where periphragm is either closely adpressed to endophragm or incompletely developed, fairly to very subdued in cysts with well-developed periphragms.
Paratabulation either not detectable or partly indicated by archeopyle development and sometimes by creases corresponding approximately to paracingular and some parasutural boundaries.
Archeopyle often undeveloped but when present appears to be a combination apical/ intercalary type, formed by opening of a ventrally adnate simple operculum fitting into a shallow depression at apex. It is sometimes slightly enlarged by secondary splitting along variably developed accessory sutures in aperture margin which delimit a number of precingular paraplates. Margin of archeopyle moderately curved in precingular series. Operculum appears to have an angular outer edge but configuration of paraplates is indeterminate.
Parasulcus occasionally indicated by longitudinal creases on ventral surface.
Paratabulation tentatively interpreted as peridiniacean; suggested formula, ?1-4", ?1 3a, 7", 0c, 5""", 2"""".
Remarks:
A small accumulation body in the mid-ventral area was noted in several cysts. Two basic morphotypes of this species were recognized. The forms that exhibit a distinctly granulate surface sculpture are generally more rounded with a less acuminate hypocystal cone, and appear to lack a pericyst, although rarely they may show incipient development of an ectophragm. By contrast, those with a laevigate periphragm, which is indicated by wrinkling and occasionally by a slight separation from the endocyst at the antapex, usually have a weakly sculptured endocyst, and commonly a more angular heart-shaped outline and a pointed antapex. The combination of characters is this second morphotype indicates more clearly the peridiniacean affinity of the species; indeed, a few of the specimens encountered display a tendency towards a "deflandreoid" appearance with a slight leftward shift of the hypocystal cone, and in one the tip of the antapex is also very slightly offset to the left in the manner of a small antapical horn.