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Amphidiadema
From Williams et al., 2017:
[Amphidiadema, Cookson and Eisenack, 1960a, p. 4; Emendation: Lentin and Williams, 1976, p. 60-61
Type species: Amphidiadema denticulata, Cookson and Eisenack, 1960a (pl.1, fig.11)]
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Original description: [Cookson and Eisenack, 1960]:
Diagnosis:
Shell elongate, without girdle, furrow, and horns, differentiated into a swollen middle portion containing a capsule which opens apically, and two smaller terminal portions, in the apical one of which a large dorsal pylome is developed.
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Emended description:
Lentin and Williams, 1976:
Description:
Pericyst: Ambitus rectangular, elongated in an antero-posterior direction. Apex concave, flat or rounded with occasionally the suggestion of an apical horn. Antapex concave, flat or rounded, commonly with one, or two, symmetrically located more or less equal antapical bulges which may represent antapical horns. Possessing an equatorial bulge with slight to prominent and determined by the size of the endocyst, being located where the endophragm and periphragm are appressed. Compression dorso-ventral.
Endocyst: Ambitus ovoidal with longest axis equatorially aligned, to circular, to longitudinally ovoidal. In contact with pericyst in precingular, cingular and postcingular regions. Compression dorso-ventral, often negligible.
Pericoels: Endocyst and pericyst separated apically and antapically by large apical and large antapical pericoel.
Phragma: Periphragm: Usually of constant thickness. Surface laevigate, granulate verrucate or denticulate.; Endophragm: Usually thicker than periphragm. Surface laevigate to sabrate to granulate.
Paratabulation: Pericyst: Paratabulation not observed. Pericingulum absent. Perisulcus absent. Endocyst: Paratabulation not observed.
Archaeopyle: Periarchaeopyle: Attenuated hexa or standard hexa intercalary resulting from the partial or complete detachment of the anterior intercalry paraplate (2a); periarchaeopyle opening primarily into the apical pericoel. When partially detached, the operculum remains attached along parasuture H4. Transverse periarchaeopyle index is 0.54-0.69. Transverse archaeopyle ratio is 1.20-2.25.
Endoarchaeopyle: Where observable appears to result from the loss of the second anterior intercalary paraplate (2a). Archaeopyle formula: I/I (2a/2a).
Dimensions:
Pericyst: Length 52-140 µm, breadth 43-64 µm;
Endocyst: Length 40-48 µm, breadth 42-60 µm
Affinities:
Amphidiadema is characterized by the rectangular ambital outline of the pericyst, the prominent equatorial bulge determined by the shape and size of the endocyst, being located where periphragm and endophragm are appressed, and the presence of a large apical and a large antapical pericoel. Isabelia differs in having an omegaform periarchaeopyle, and apical and antapical horns.
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Modified description:
Stover and Evitt, 1978, p. 92-93:
Synopsis:
Cysts bicavate, compressed elongate; endophragm outline broadly elliptical; substantial epicoel and hypocoel narrower than endocyst and clearly separated by intermediate zone of contact between endophragm and periphragm; paratabulation indicated by archeopyle only, latter intercalary, Type l/l; archeopyle index <0.5.
Description:
Shape: Compressed elongate; apical and antapical extensions narrower than middle part and broadly rounded or truncate.
Wall relationships: Cysts bicavate; endophragm and periphragm appressed between prominent epicoel and hypocoel of similar size and shape.
Wall features: No parasutural features. Periphragm smooth or ornamented with features of low relief.
Paratabulation: Indicated by archeopyle only.
Archeopyle: Intercalary, Type 1/1 (2a only); archeopyle index <0.5; operculum free.
Paracingulum: Not indicated.
Parasulcus: Not indicated.
Size: Intermediate.
Affinities:
The absence of horns, together with the narrow (relative to the width of the endocyst) well developed epi- and hypocoels, serve to differentiate Amphidiadema from other cavate genera possessing small Type I or I/l archeopyles.
[Amphidiadema, Cookson and Eisenack, 1960a, p. 4; Emendation: Lentin and Williams, 1976, p. 60-61
Type species: Amphidiadema denticulata, Cookson and Eisenack, 1960a (pl.1, fig.11)]
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Original description: [Cookson and Eisenack, 1960]:
Diagnosis:
Shell elongate, without girdle, furrow, and horns, differentiated into a swollen middle portion containing a capsule which opens apically, and two smaller terminal portions, in the apical one of which a large dorsal pylome is developed.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Emended description:
Lentin and Williams, 1976:
Description:
Pericyst: Ambitus rectangular, elongated in an antero-posterior direction. Apex concave, flat or rounded with occasionally the suggestion of an apical horn. Antapex concave, flat or rounded, commonly with one, or two, symmetrically located more or less equal antapical bulges which may represent antapical horns. Possessing an equatorial bulge with slight to prominent and determined by the size of the endocyst, being located where the endophragm and periphragm are appressed. Compression dorso-ventral.
Endocyst: Ambitus ovoidal with longest axis equatorially aligned, to circular, to longitudinally ovoidal. In contact with pericyst in precingular, cingular and postcingular regions. Compression dorso-ventral, often negligible.
Pericoels: Endocyst and pericyst separated apically and antapically by large apical and large antapical pericoel.
Phragma: Periphragm: Usually of constant thickness. Surface laevigate, granulate verrucate or denticulate.; Endophragm: Usually thicker than periphragm. Surface laevigate to sabrate to granulate.
Paratabulation: Pericyst: Paratabulation not observed. Pericingulum absent. Perisulcus absent. Endocyst: Paratabulation not observed.
Archaeopyle: Periarchaeopyle: Attenuated hexa or standard hexa intercalary resulting from the partial or complete detachment of the anterior intercalry paraplate (2a); periarchaeopyle opening primarily into the apical pericoel. When partially detached, the operculum remains attached along parasuture H4. Transverse periarchaeopyle index is 0.54-0.69. Transverse archaeopyle ratio is 1.20-2.25.
Endoarchaeopyle: Where observable appears to result from the loss of the second anterior intercalary paraplate (2a). Archaeopyle formula: I/I (2a/2a).
Dimensions:
Pericyst: Length 52-140 µm, breadth 43-64 µm;
Endocyst: Length 40-48 µm, breadth 42-60 µm
Affinities:
Amphidiadema is characterized by the rectangular ambital outline of the pericyst, the prominent equatorial bulge determined by the shape and size of the endocyst, being located where periphragm and endophragm are appressed, and the presence of a large apical and a large antapical pericoel. Isabelia differs in having an omegaform periarchaeopyle, and apical and antapical horns.
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Modified description:
Stover and Evitt, 1978, p. 92-93:
Synopsis:
Cysts bicavate, compressed elongate; endophragm outline broadly elliptical; substantial epicoel and hypocoel narrower than endocyst and clearly separated by intermediate zone of contact between endophragm and periphragm; paratabulation indicated by archeopyle only, latter intercalary, Type l/l; archeopyle index <0.5.
Description:
Shape: Compressed elongate; apical and antapical extensions narrower than middle part and broadly rounded or truncate.
Wall relationships: Cysts bicavate; endophragm and periphragm appressed between prominent epicoel and hypocoel of similar size and shape.
Wall features: No parasutural features. Periphragm smooth or ornamented with features of low relief.
Paratabulation: Indicated by archeopyle only.
Archeopyle: Intercalary, Type 1/1 (2a only); archeopyle index <0.5; operculum free.
Paracingulum: Not indicated.
Parasulcus: Not indicated.
Size: Intermediate.
Affinities:
The absence of horns, together with the narrow (relative to the width of the endocyst) well developed epi- and hypocoels, serve to differentiate Amphidiadema from other cavate genera possessing small Type I or I/l archeopyles.