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Isabelidinium
From Williams et al., 2017:
[Isabelidinium, Lentin and Williams, 1977a, p. 167; Emendations: Marshall, 1988, p. 203, 205; Fensome et al., 2009, p. 39.
Marshall (1988, p.205) suggested that Manumiella may be a taxonomic junior synonym of this genus.
Type species: originally as Deflandrea korojonensis, Cookson and Eisenack, 1958 (pl.4, fig.10)] ; Isabelidinium korojonense, Lentin and Williams, 1977
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Original description: [Lentin and Williams, 1976]: (Isabelia; taken from Stover and Evitt, 1978, p. 108; major headings deleted and paragraphing modified)
Description:
Pericyst: Ambitus commonly pentagonal, elongated in an anteroposterior direction, rarely rhomboidal or rectangular. Apex prolonged into a broad short apical horn which may merge imperceptibly into the epipericyst, or be developed into shoulders. Antapex produced into two symmetrically located short antapical horns, usually of unequal length. The left antapical horn is always the longer, the right is reduced or vestigial. The apical and two antapical horns sometimes reduced. There is usually a slight to prominent equatorial bulge in ambital view. Compression dorsoventral.
Endocyst: Ambitus ovoidal with longest axis equatorially aligned to circular, to elongate ovoidal. May be equatorially in contact with endocyst. Pericoels: When endocyst and pericyst are appressed in precingular, cingular and postcingular regions, they are separated apically and antapically by a large apical and a large antapical pericoel, respectively. Alternatively the apical and antapical pericoels may be united by an ambital pericoel. Compression dorsoventral, may be negligible.
Periphragm: Usually of constant thickness. Surface levigate, scabrate, granulate or verrucate. Ornamentation nontabular.
Endophragm: Surface levigate to scabrate to granulate.
Pericyst: Paratabulation indeterminate other than in the vicinity of the periarcheopyle.
Pericingulum: Almost always absent or rudimentary and never complete, occasionally visible on the ambitus as an indentation.
Perisulcus: Not observed.
Endocyst: Paratabulation unknown.
Periarcheopyle: Omegaform intercalary resulting from the partial detachment of the second anterior intercalary paraplate, 2a, with perioperculum usually remaining attached along parasuture H4. Transverse periarcheopyle index is 0.33-0.55. Transverse archeopyle ratio is 0.50-1.25.
Endoarcheopyle: Where observable appears to result from the loss of the second anterior intercalary paraplate (2a), or all three anterior intercalaries.
Archeopyle Formula: I/I (2a/2a) or I/3I (2a/1-3a).
Affinities:
Isabelia: Isabelia closely resembles Chatangiella in possessing an omegaform periarchaeopyle which seems to be related to the outline of the epipericyst, which in such taxa is commonly widest in the vicinity of the archaeopyle. However, Chatangiella has a hepta/pentapartite pericingulum and frequently penetabular ornamentation.
Alterbia differs in possessing a pericingulum and a standard to attenuated hexa periarchaeopyle. The apical horn and left antapical horn also tend to be more prominent in Alterbia.
Amphidiadema which lacks a pericingulum differs from Isabelia in having a standard hexa or attenuated hexa periarchaeopyle, and apical and antapical regions devoid of horns.
Trithyrodinium has the distinctive 3I (1-3a) periarchaeopyle.
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Modified description:
Stover and Evit, 1978, p. 108-109:
Synopsis:
Cysts proximate, bicavate or circumcavate, compressed; outline generally longitudinally elongate, less commonly subtriangular to subcircular; a single apical and two antapical horns normally poorly developed or may be lacking altogether; endocyst occupies central portion of pericyst; endocyst outline circular to elliptical, length equal to or less than width; paratabulation indicated by archeopyle only, or by paracingulum and archeopyle; latter intercalary, Type I or Ia; archeopyle index <0.5, usually about 0.3.
Description:
Shape: Cysts compressed; outline generally longitudinally elongate, occasionally subtriangular to subcircular; apical and antapical horns typically weakly developed, and may be absent.
Wall relationships: Cysts bicavate or circumcavate; endocyst outline circular to elliptical, length equal to or less than width; endocyst occupies central portion of pericyst.
Wall features : No parasutural features. Periphragm smooth or ornamented with features of low to moderate relief; ornamentation distributed uniformly, dense or widely scattered.
Paratabulation: Generally indicated by archeopyle only or by archeopyle and paracingulum; other indications indistinct and inconsistent.
Archaeopyle: Intercalary, Type I or Ia (2a only); archeopyle index <0.5, usually about 0.3; operculum free or attached antapically.
Paracingulum: Not indicated, or expressed by low parallel transverse folds or ridges; rarely expressed laterally.
Parasulcus: Generally not indicated, or expressed as poorly defined depression on the hypocyst.
Size: Intermediate to large.
Affinities:
Isabelidinium differs from Nelsoniella and Eucladinium in that the endocyst occupies the central portion of the pericyst rather than mainly the posterior portion. The outline of the endocyst in Isabelidinium is circular to subcircular, with the length being equal to or less than the width. In Eurydinium and Xenikoon the outline of the endocyst is elliptical, with the length being greater than the width.
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Emended descriptions:
Marshall, 1988:
Diagnosis:
Cysts intermediate to large, compressed ventrodorsally, often with a weak to pronounced mid-dorsal bulge, equidimensional or longitudinally elongate. Lateral margins evenly convex near equator, each rarely modified by a weak equatorial bulge. Polar areas evenly convex or modified by 1 apical and 1-2 antapical horns. Cysts bicavate or circumcavate, rarely cornucavate. Endocyst subcircular to ovoidal, may be slightly elongate along longitudinal or transverse axis; occupying central portion of pericyst.
Endophragm and periphragm smooth or bearing elements of low to moderate relief (e.g. granulate, verrucate, or rugulate). Periphragm ornament fairly evenly distributed over polar areas, frequently becoming sparse to absent on mid-dorsal and mid-ventral surfaces. Periphragm occasionally perforate; on some forms, pores and associated ridges aligned along parasutural boundaries.
Paratabulation indicated by archeopyle and parasutural features, peridiniacean, formula incomplete: 3` (1`, 3`, 4`), 3a, 7``, 4``` (1-4```), 2````, Xs. Archeopyle intercalary, Type I or Ia (2a only), deltaform to thetaform, operculum attached posteriorly.
Paracingulum absent or faintly indicated by 2 parallel, transverse ridges separated by a shallow groove extending around dorsal and edges of ventral surfaces. Ridges continuous or partite. Parasulcus usually weakly defined by a shallow longitudinal groove on mid-ventral surface.
Discussion:
Unlike Stover & Evitt ( 1978, p. 1 08), I include forms with rows of parasutural markings and a weakly defined paracingulum with a panite structure. The periarcheopyle of the type species, as discussed by Marshall (in press), is interpreted as deltaform to thetaform, not iso-omegaform (Bujak & Davies, 1983). Other species assigned by Lentin & Williams (1985) also have deltaform to thetaform periarcheopyles. Bujak & Davies ( 1983) considered Isabelidinium to differ from Manumiella Bujak & Davies, 1983 in having an omegaform periarcheopyle and being bicavate but neither feature permits reliable separation; they may prove synonymous. Isabelidinium differs from Chatangiella mainly in lacking a pronounced paracingulum with a partite structure. There also appear to be differences in the ranges of the periarcheopyle outline, that of Chatangiella extending from thetaform to omegaform.
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Fensome et al., 2009:
Diagnosis:
Peridiniacean (deflandreoid) cysts that are proximate, dorsoventrally compressed and peridinioid in outline, commonly with epicystal 'shoulders' and asymmetrical antapex, the left side being larger. Circumcavate to bicavate. Surface generally tabulate to weakly paratabulate.
Periarchaeopyle intercalary, with formula I2a , operculum free or posteriorly attached; plate 2a is isodelta form to iso-omegaform; endoarchaeopyle similar or in volving all three intercalary plates, with formula I1a+2a+3a.
Remarks:
The above emended diagnosis can also serve as a synopsis. The genus Isabelidinium was originally conceived as a form similar to Chatangiella but without a partite cingulum, and the type of the genus - the holotype of Deflandrea korojonense (Cookson & Eisenack 1958: pl. 4, fig 10) - reflects this concept. However, as pointed out by Marshall (1988:203,205, who proposed an emendation for this genus), other species attributed to the genus do not conform to the original concept, and there has developed some overlap with other genera, such as Manumiella. Here, we focus the diagnosis of Isabelidinium, restricting it to forms generally with 'shoulders', two asymmetrical antapical horns and, generally, an iso-thetaform to iso-omegaform archaeopyle. Chatangiella has a partite cingulum and a consistently iso-omegaform archaeopyle, Cerodinium has an isodeltaform archaeopyle, a symmetrical antapex and no 'shoulders', and Alterbidinium has an isodeltaform to stenodeltaform 2a and a more variable, if consistently asymmetrical, antapex. Marshall (1988) speculated that Manumiella might be regarded as a junior taxonomic synonym of Isabelidinium; however, since herein we restrict Manumiella to forms with a single antapical horn, the two genera can be maintained separately.
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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.
Isabelidinium Lentin and Williams, 1977a, emend. Marshall, 1988, was emended by Marshall (1988, p.203,205), who noted that paratabulation is indicated by the archeopyle and parasutural features, with the paracingulum being absent or faintly indicated by two parallel, transverse ridges, separated by a shallow groove extending around dorsal and edges of ventral surfaces. The archeopyle, he stated, is deltaform to thetaform, with the operculum attached posteriorly. Marshall further noted that Manumiella may be a taxonomic junior synonym of Isabelidinium .
[Isabelidinium, Lentin and Williams, 1977a, p. 167; Emendations: Marshall, 1988, p. 203, 205; Fensome et al., 2009, p. 39.
Marshall (1988, p.205) suggested that Manumiella may be a taxonomic junior synonym of this genus.
Type species: originally as Deflandrea korojonensis, Cookson and Eisenack, 1958 (pl.4, fig.10)] ; Isabelidinium korojonense, Lentin and Williams, 1977
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Lentin and Williams, 1976]: (Isabelia; taken from Stover and Evitt, 1978, p. 108; major headings deleted and paragraphing modified)
Description:
Pericyst: Ambitus commonly pentagonal, elongated in an anteroposterior direction, rarely rhomboidal or rectangular. Apex prolonged into a broad short apical horn which may merge imperceptibly into the epipericyst, or be developed into shoulders. Antapex produced into two symmetrically located short antapical horns, usually of unequal length. The left antapical horn is always the longer, the right is reduced or vestigial. The apical and two antapical horns sometimes reduced. There is usually a slight to prominent equatorial bulge in ambital view. Compression dorsoventral.
Endocyst: Ambitus ovoidal with longest axis equatorially aligned to circular, to elongate ovoidal. May be equatorially in contact with endocyst. Pericoels: When endocyst and pericyst are appressed in precingular, cingular and postcingular regions, they are separated apically and antapically by a large apical and a large antapical pericoel, respectively. Alternatively the apical and antapical pericoels may be united by an ambital pericoel. Compression dorsoventral, may be negligible.
Periphragm: Usually of constant thickness. Surface levigate, scabrate, granulate or verrucate. Ornamentation nontabular.
Endophragm: Surface levigate to scabrate to granulate.
Pericyst: Paratabulation indeterminate other than in the vicinity of the periarcheopyle.
Pericingulum: Almost always absent or rudimentary and never complete, occasionally visible on the ambitus as an indentation.
Perisulcus: Not observed.
Endocyst: Paratabulation unknown.
Periarcheopyle: Omegaform intercalary resulting from the partial detachment of the second anterior intercalary paraplate, 2a, with perioperculum usually remaining attached along parasuture H4. Transverse periarcheopyle index is 0.33-0.55. Transverse archeopyle ratio is 0.50-1.25.
Endoarcheopyle: Where observable appears to result from the loss of the second anterior intercalary paraplate (2a), or all three anterior intercalaries.
Archeopyle Formula: I/I (2a/2a) or I/3I (2a/1-3a).
Affinities:
Isabelia: Isabelia closely resembles Chatangiella in possessing an omegaform periarchaeopyle which seems to be related to the outline of the epipericyst, which in such taxa is commonly widest in the vicinity of the archaeopyle. However, Chatangiella has a hepta/pentapartite pericingulum and frequently penetabular ornamentation.
Alterbia differs in possessing a pericingulum and a standard to attenuated hexa periarchaeopyle. The apical horn and left antapical horn also tend to be more prominent in Alterbia.
Amphidiadema which lacks a pericingulum differs from Isabelia in having a standard hexa or attenuated hexa periarchaeopyle, and apical and antapical regions devoid of horns.
Trithyrodinium has the distinctive 3I (1-3a) periarchaeopyle.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Modified description:
Stover and Evit, 1978, p. 108-109:
Synopsis:
Cysts proximate, bicavate or circumcavate, compressed; outline generally longitudinally elongate, less commonly subtriangular to subcircular; a single apical and two antapical horns normally poorly developed or may be lacking altogether; endocyst occupies central portion of pericyst; endocyst outline circular to elliptical, length equal to or less than width; paratabulation indicated by archeopyle only, or by paracingulum and archeopyle; latter intercalary, Type I or Ia; archeopyle index <0.5, usually about 0.3.
Description:
Shape: Cysts compressed; outline generally longitudinally elongate, occasionally subtriangular to subcircular; apical and antapical horns typically weakly developed, and may be absent.
Wall relationships: Cysts bicavate or circumcavate; endocyst outline circular to elliptical, length equal to or less than width; endocyst occupies central portion of pericyst.
Wall features : No parasutural features. Periphragm smooth or ornamented with features of low to moderate relief; ornamentation distributed uniformly, dense or widely scattered.
Paratabulation: Generally indicated by archeopyle only or by archeopyle and paracingulum; other indications indistinct and inconsistent.
Archaeopyle: Intercalary, Type I or Ia (2a only); archeopyle index <0.5, usually about 0.3; operculum free or attached antapically.
Paracingulum: Not indicated, or expressed by low parallel transverse folds or ridges; rarely expressed laterally.
Parasulcus: Generally not indicated, or expressed as poorly defined depression on the hypocyst.
Size: Intermediate to large.
Affinities:
Isabelidinium differs from Nelsoniella and Eucladinium in that the endocyst occupies the central portion of the pericyst rather than mainly the posterior portion. The outline of the endocyst in Isabelidinium is circular to subcircular, with the length being equal to or less than the width. In Eurydinium and Xenikoon the outline of the endocyst is elliptical, with the length being greater than the width.
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Emended descriptions:
Marshall, 1988:
Diagnosis:
Cysts intermediate to large, compressed ventrodorsally, often with a weak to pronounced mid-dorsal bulge, equidimensional or longitudinally elongate. Lateral margins evenly convex near equator, each rarely modified by a weak equatorial bulge. Polar areas evenly convex or modified by 1 apical and 1-2 antapical horns. Cysts bicavate or circumcavate, rarely cornucavate. Endocyst subcircular to ovoidal, may be slightly elongate along longitudinal or transverse axis; occupying central portion of pericyst.
Endophragm and periphragm smooth or bearing elements of low to moderate relief (e.g. granulate, verrucate, or rugulate). Periphragm ornament fairly evenly distributed over polar areas, frequently becoming sparse to absent on mid-dorsal and mid-ventral surfaces. Periphragm occasionally perforate; on some forms, pores and associated ridges aligned along parasutural boundaries.
Paratabulation indicated by archeopyle and parasutural features, peridiniacean, formula incomplete: 3` (1`, 3`, 4`), 3a, 7``, 4``` (1-4```), 2````, Xs. Archeopyle intercalary, Type I or Ia (2a only), deltaform to thetaform, operculum attached posteriorly.
Paracingulum absent or faintly indicated by 2 parallel, transverse ridges separated by a shallow groove extending around dorsal and edges of ventral surfaces. Ridges continuous or partite. Parasulcus usually weakly defined by a shallow longitudinal groove on mid-ventral surface.
Discussion:
Unlike Stover & Evitt ( 1978, p. 1 08), I include forms with rows of parasutural markings and a weakly defined paracingulum with a panite structure. The periarcheopyle of the type species, as discussed by Marshall (in press), is interpreted as deltaform to thetaform, not iso-omegaform (Bujak & Davies, 1983). Other species assigned by Lentin & Williams (1985) also have deltaform to thetaform periarcheopyles. Bujak & Davies ( 1983) considered Isabelidinium to differ from Manumiella Bujak & Davies, 1983 in having an omegaform periarcheopyle and being bicavate but neither feature permits reliable separation; they may prove synonymous. Isabelidinium differs from Chatangiella mainly in lacking a pronounced paracingulum with a partite structure. There also appear to be differences in the ranges of the periarcheopyle outline, that of Chatangiella extending from thetaform to omegaform.
----------------------------------
Fensome et al., 2009:
Diagnosis:
Peridiniacean (deflandreoid) cysts that are proximate, dorsoventrally compressed and peridinioid in outline, commonly with epicystal 'shoulders' and asymmetrical antapex, the left side being larger. Circumcavate to bicavate. Surface generally tabulate to weakly paratabulate.
Periarchaeopyle intercalary, with formula I2a , operculum free or posteriorly attached; plate 2a is isodelta form to iso-omegaform; endoarchaeopyle similar or in volving all three intercalary plates, with formula I1a+2a+3a.
Remarks:
The above emended diagnosis can also serve as a synopsis. The genus Isabelidinium was originally conceived as a form similar to Chatangiella but without a partite cingulum, and the type of the genus - the holotype of Deflandrea korojonense (Cookson & Eisenack 1958: pl. 4, fig 10) - reflects this concept. However, as pointed out by Marshall (1988:203,205, who proposed an emendation for this genus), other species attributed to the genus do not conform to the original concept, and there has developed some overlap with other genera, such as Manumiella. Here, we focus the diagnosis of Isabelidinium, restricting it to forms generally with 'shoulders', two asymmetrical antapical horns and, generally, an iso-thetaform to iso-omegaform archaeopyle. Chatangiella has a partite cingulum and a consistently iso-omegaform archaeopyle, Cerodinium has an isodeltaform archaeopyle, a symmetrical antapex and no 'shoulders', and Alterbidinium has an isodeltaform to stenodeltaform 2a and a more variable, if consistently asymmetrical, antapex. Marshall (1988) speculated that Manumiella might be regarded as a junior taxonomic synonym of Isabelidinium; however, since herein we restrict Manumiella to forms with a single antapical horn, the two genera can be maintained separately.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Notes:
G.L. Williams short notes on species, Mesozoic-Cenozoic dinocyst course, Urbino, Italy, May 17-22, 1999 - LPP VIEWER CD-ROM 99.5.
Isabelidinium Lentin and Williams, 1977a, emend. Marshall, 1988, was emended by Marshall (1988, p.203,205), who noted that paratabulation is indicated by the archeopyle and parasutural features, with the paracingulum being absent or faintly indicated by two parallel, transverse ridges, separated by a shallow groove extending around dorsal and edges of ventral surfaces. The archeopyle, he stated, is deltaform to thetaform, with the operculum attached posteriorly. Marshall further noted that Manumiella may be a taxonomic junior synonym of Isabelidinium .