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Dinogymnium
From Williams et al., 2017:
[Dinogymnium, Evitt et al., 1967, p. 4-8; Emendation: Lentin and Vozzhennikova, 1990, p. 14-15
Type species: Dinogymnium acuminatum, Evitt et al., 1967 (pl.1, figs.21–23; pl.2, fig.5; text-figs.16–18)]
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Original description: [Evitt et al., 1967]:
Diagnosis:
Tests of variable size and shape, commonly exhibiting a strong superficial similarity to motile cells of the modern genus Gymnodinium Stein; without indications of tabulation and without an inner body. Some species are characterized by a few to numerous longitudinal folds or ribs, but in other species these folds may be feebly developed or wholly lacking. Cingulum usually, but not always, distinct and moderately to deeply incised; circular to spiral with a ventral offset of about one cingulum width; not crossed by septa or other projections. Sulcus, while clearly developed, apparently confined to the hypotract, but a fold in the epitract often lies in line with the sulcus and may appear to be a simple continuation of it. Surface smooth or ornamented with small features (e.g., scabrae, granules, or pustules); normally without spines and other large projections. Wall partially or completely penetrated by many wall-canals which vary in diameter, inclination, and distribution although they are usually under o.s microns in diameter and about perpendicular to the surface. Apex occupied by a small, but usually distinct, archeopyle.
Affinities:
Dinogymnium is distinguished from Gymnodinium by the thickness, resistance, and structure of its wall, and by the presence of an archeopyle. These features are without known counterpart in any modern species of Gymnodinium.
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Emended description:
Lentin and Vozzhennikova, 1990:
Description:
Fossil dinoflagellates which are biconal to roundly biconal; the epicyst may be somewhat longer than the hypocyst (Cingulum Index = 40-60). The autophragm may be smooth, granulose or microporate with longitudinal ridges on both the epicyst and hypocyst which extend to or nearly to the apex and antapex. The archeopyle is formed by two arcuate sutures of equal length which result in the loss of a single paraplate at the apex of the cyst. The paracingulum is shallow to deep, dividing the cyst into two more or less equal portions; the epicyst may be somewhat longer than the hypocyst. The parasulcus is indicated by a shallow longitudinal depression, principally on the hypocyst, immediately below the paracingulum.
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Modified description:
Stover and Evitt, 1978, p. 37:
Synopsis:
Cysts biconical to ellipsoidal, autophragm only, with few to many longitudinal folds or ribs; equatorial to subequatorial paracingulum usually discernible; parasulcus apparently confined to hypocyst; archeopyle small, apical, and atypical.
Description:
Shape: Biconical to ellipsoidal.
Wall relationships: Autophragm only.
Wall features: No parasutural features. Few to many longitudinal folds or ribs commonly present; may be weakly developed or absent. Autophragm smooth or with features of low relief that may be partly or completely penetrated by wall canals.
Paratabulation: None indicated.
Archeopyle: Apical, small, and atypical; formed by two arcuate sutures that meet or almost meet dorsally and ventrally; operculum dorso-ventrally elongate, transversely narrow.
Paracingulum: Indicated usually by a moderately shallow to deep equatorial to subequatorial concavity.
Parasulcus: Indicated by a shallow longitudinal depression principally on the hypocyst; parasulcus rarely well developed and may not be discernible.
Size: Small to large.
Affinities:
We restrict the genus Dinogymnium to those species which are distinctly biconical to roundly biconical and which have a cingulum index between 40 and 60. That is, the epicyst and hypocyst are approximately equal in length.
[Dinogymnium, Evitt et al., 1967, p. 4-8; Emendation: Lentin and Vozzhennikova, 1990, p. 14-15
Type species: Dinogymnium acuminatum, Evitt et al., 1967 (pl.1, figs.21–23; pl.2, fig.5; text-figs.16–18)]
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Original description: [Evitt et al., 1967]:
Diagnosis:
Tests of variable size and shape, commonly exhibiting a strong superficial similarity to motile cells of the modern genus Gymnodinium Stein; without indications of tabulation and without an inner body. Some species are characterized by a few to numerous longitudinal folds or ribs, but in other species these folds may be feebly developed or wholly lacking. Cingulum usually, but not always, distinct and moderately to deeply incised; circular to spiral with a ventral offset of about one cingulum width; not crossed by septa or other projections. Sulcus, while clearly developed, apparently confined to the hypotract, but a fold in the epitract often lies in line with the sulcus and may appear to be a simple continuation of it. Surface smooth or ornamented with small features (e.g., scabrae, granules, or pustules); normally without spines and other large projections. Wall partially or completely penetrated by many wall-canals which vary in diameter, inclination, and distribution although they are usually under o.s microns in diameter and about perpendicular to the surface. Apex occupied by a small, but usually distinct, archeopyle.
Affinities:
Dinogymnium is distinguished from Gymnodinium by the thickness, resistance, and structure of its wall, and by the presence of an archeopyle. These features are without known counterpart in any modern species of Gymnodinium.
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Emended description:
Lentin and Vozzhennikova, 1990:
Description:
Fossil dinoflagellates which are biconal to roundly biconal; the epicyst may be somewhat longer than the hypocyst (Cingulum Index = 40-60). The autophragm may be smooth, granulose or microporate with longitudinal ridges on both the epicyst and hypocyst which extend to or nearly to the apex and antapex. The archeopyle is formed by two arcuate sutures of equal length which result in the loss of a single paraplate at the apex of the cyst. The paracingulum is shallow to deep, dividing the cyst into two more or less equal portions; the epicyst may be somewhat longer than the hypocyst. The parasulcus is indicated by a shallow longitudinal depression, principally on the hypocyst, immediately below the paracingulum.
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Modified description:
Stover and Evitt, 1978, p. 37:
Synopsis:
Cysts biconical to ellipsoidal, autophragm only, with few to many longitudinal folds or ribs; equatorial to subequatorial paracingulum usually discernible; parasulcus apparently confined to hypocyst; archeopyle small, apical, and atypical.
Description:
Shape: Biconical to ellipsoidal.
Wall relationships: Autophragm only.
Wall features: No parasutural features. Few to many longitudinal folds or ribs commonly present; may be weakly developed or absent. Autophragm smooth or with features of low relief that may be partly or completely penetrated by wall canals.
Paratabulation: None indicated.
Archeopyle: Apical, small, and atypical; formed by two arcuate sutures that meet or almost meet dorsally and ventrally; operculum dorso-ventrally elongate, transversely narrow.
Paracingulum: Indicated usually by a moderately shallow to deep equatorial to subequatorial concavity.
Parasulcus: Indicated by a shallow longitudinal depression principally on the hypocyst; parasulcus rarely well developed and may not be discernible.
Size: Small to large.
Affinities:
We restrict the genus Dinogymnium to those species which are distinctly biconical to roundly biconical and which have a cingulum index between 40 and 60. That is, the epicyst and hypocyst are approximately equal in length.