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Williamsidinium
From Williams et al., 2017:
[Williamsidinium, Lentin, 1983, p. 148,150
Type species: Williamsidinium banksianum, Lentin, 1983 (pl.1, figs.1a–b)]
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Original description: [Lentin, 1983]:
Description:
Pericyst ambitus rhomboidal to subpentagonal, elongated in an anterior-posterior direction. Pericyst prolonged into one apical and two symmetrically placed antapical horns, the right antapical generally reduced or vestigial. The pericyst attains its greatest width in the region of the pericingulum. Cyst dorsoventrally compressed.
Endocyst ambitus circular to ovoidal to rhomboidal in dorsoventral view. May be in contact with pericyst in precingular, cingular and postcingular regions as Williamsidinium banksianum gen. well as the base of the intercalary paraplates. Apical and antapical pericoels always present. The apical and antapical pericoels may be united by an ambital pericoel.
Thickness of the periphragm variable but usually about 1µm. Surface generally laevigate, occasionally scabrate, granulate, or verrucate. The endophragm rarely exceeds 1µm and is of constant thickness. Surface generally laevigate.
Paratabulation indeterminate except in the vicinity of the periarcheopyle which indicates a peridinioid style of tabulation.
Paracingulum may or may not be well developed, planar or slightly helicoidal, with anterior parasuture only, or anterior and posterior parasuture as a slightly raised ridge or border, with smooth or denticulate margins.
The parasulcus is rarely determinable; when visible largely restricted to the hypopericyst. A flagellar scar is sometimes visible.
No observable paratabulation on the endocyst except in the vicinity of the endoarcheopyle.
The archeopyle is a combination archeopyle with the formula 3 IP@. Compound operculum with 1a, 2a, and 3a separating laterally but remaining
attached to the 3", 4", and 5" respectively. Accessory archeopyle sutures may be partially or completely developed between the precingular paraplates 2"-3", 3"-4", 4"-5", and 5"-6". The shape of the 2a plate is attenuated hexa to standard hexa. The la and 3a are very large.
The endophragm and periphragm are appressed near the base of the intercalary paraplates. As a result the endoperculum is usually attached to the perioperculum. Rarely one or more intercalary paraplates from the endoperculum may be found within the endocoel.
The archeopyle formula is: 3 IP@ (1 a+3"@ + 2a+4"@ + 3a+5"@)
A periopisthopyle (ventral antapical opening) may be formed between the antapical horns
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Modified description:
Stover and Williams, 1987, p. 227:
Synopsis:
Cysts proximate, compressed dorsoventrally, bicavate or circumcavate; outline of endocyst subcircular, outline of pericyst roundly pentagonal with an apical and left antapical horn; right antapical horn absent or reduced; combined intercalary and precingular archeopyle, type 3 IP @; intercalary paraplates not separated from subjacent precingulars, which in turn are adnate posteriorly.
Description:
Shape: Cysts compressed dorsoventrally; pericyst outline roundly pentagonal, longitudinally elongate with an apical and left antapical horn; right antapical horn reduced or absent; endocyst outline subcircular.
Wall relationships: Cysts bicavate or circumcavate.
Wall features: Endocyst generally smooth; pericyst smooth to ornamented with features of low relief.
Archeopyle: Combined intercalary and precingular, type 3 IP @, 2a biplanate; individual intercalary paraplates (1 a-3a) separated laterally but not separated from subjacent precingular paraplates (3-5", respectively); combined intercalary and precingular paraplates adnate posteriorly. Evidently, paraplates both in the periphragm and endophragm involved in archeopyle formation.
Paratabulation: Indicated generally by archeopyle only; 2a paraplate hexastyle.
Paracingulum: Not indicated, or expressed by one (anterior) or two transverse ridges with or without denticulate margins.
Parasulcus: Rarely determinable.
Size: Intermediate, length 60 to 85 µm.
Affinities:
In shape, Williamsidinium resembles Alterbidinium Lentin and Williams 1985 and Isabelidinium Lentin and Williams 1977a, but Williamsidinium has a 3 IP @ archeopyle rather than a simple I (2a) archeopyle. Laciniadinium Mclntyre 1975 possesses a [313P]@ archeopyle, but evidently lacks the accessory sutures separating longitudinally-paired intercalary and precingular paraplates. The same applies to Luxadinium Brideaux and Mclntyre 1975, when the archeopyle type is [313P]@; when it is 313P, up to six opercular pieces may be released.
[Williamsidinium, Lentin, 1983, p. 148,150
Type species: Williamsidinium banksianum, Lentin, 1983 (pl.1, figs.1a–b)]
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Original description: [Lentin, 1983]:
Description:
Pericyst ambitus rhomboidal to subpentagonal, elongated in an anterior-posterior direction. Pericyst prolonged into one apical and two symmetrically placed antapical horns, the right antapical generally reduced or vestigial. The pericyst attains its greatest width in the region of the pericingulum. Cyst dorsoventrally compressed.
Endocyst ambitus circular to ovoidal to rhomboidal in dorsoventral view. May be in contact with pericyst in precingular, cingular and postcingular regions as Williamsidinium banksianum gen. well as the base of the intercalary paraplates. Apical and antapical pericoels always present. The apical and antapical pericoels may be united by an ambital pericoel.
Thickness of the periphragm variable but usually about 1µm. Surface generally laevigate, occasionally scabrate, granulate, or verrucate. The endophragm rarely exceeds 1µm and is of constant thickness. Surface generally laevigate.
Paratabulation indeterminate except in the vicinity of the periarcheopyle which indicates a peridinioid style of tabulation.
Paracingulum may or may not be well developed, planar or slightly helicoidal, with anterior parasuture only, or anterior and posterior parasuture as a slightly raised ridge or border, with smooth or denticulate margins.
The parasulcus is rarely determinable; when visible largely restricted to the hypopericyst. A flagellar scar is sometimes visible.
No observable paratabulation on the endocyst except in the vicinity of the endoarcheopyle.
The archeopyle is a combination archeopyle with the formula 3 IP@. Compound operculum with 1a, 2a, and 3a separating laterally but remaining
attached to the 3", 4", and 5" respectively. Accessory archeopyle sutures may be partially or completely developed between the precingular paraplates 2"-3", 3"-4", 4"-5", and 5"-6". The shape of the 2a plate is attenuated hexa to standard hexa. The la and 3a are very large.
The endophragm and periphragm are appressed near the base of the intercalary paraplates. As a result the endoperculum is usually attached to the perioperculum. Rarely one or more intercalary paraplates from the endoperculum may be found within the endocoel.
The archeopyle formula is: 3 IP@ (1 a+3"@ + 2a+4"@ + 3a+5"@)
A periopisthopyle (ventral antapical opening) may be formed between the antapical horns
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Modified description:
Stover and Williams, 1987, p. 227:
Synopsis:
Cysts proximate, compressed dorsoventrally, bicavate or circumcavate; outline of endocyst subcircular, outline of pericyst roundly pentagonal with an apical and left antapical horn; right antapical horn absent or reduced; combined intercalary and precingular archeopyle, type 3 IP @; intercalary paraplates not separated from subjacent precingulars, which in turn are adnate posteriorly.
Description:
Shape: Cysts compressed dorsoventrally; pericyst outline roundly pentagonal, longitudinally elongate with an apical and left antapical horn; right antapical horn reduced or absent; endocyst outline subcircular.
Wall relationships: Cysts bicavate or circumcavate.
Wall features: Endocyst generally smooth; pericyst smooth to ornamented with features of low relief.
Archeopyle: Combined intercalary and precingular, type 3 IP @, 2a biplanate; individual intercalary paraplates (1 a-3a) separated laterally but not separated from subjacent precingular paraplates (3-5", respectively); combined intercalary and precingular paraplates adnate posteriorly. Evidently, paraplates both in the periphragm and endophragm involved in archeopyle formation.
Paratabulation: Indicated generally by archeopyle only; 2a paraplate hexastyle.
Paracingulum: Not indicated, or expressed by one (anterior) or two transverse ridges with or without denticulate margins.
Parasulcus: Rarely determinable.
Size: Intermediate, length 60 to 85 µm.
Affinities:
In shape, Williamsidinium resembles Alterbidinium Lentin and Williams 1985 and Isabelidinium Lentin and Williams 1977a, but Williamsidinium has a 3 IP @ archeopyle rather than a simple I (2a) archeopyle. Laciniadinium Mclntyre 1975 possesses a [313P]@ archeopyle, but evidently lacks the accessory sutures separating longitudinally-paired intercalary and precingular paraplates. The same applies to Luxadinium Brideaux and Mclntyre 1975, when the archeopyle type is [313P]@; when it is 313P, up to six opercular pieces may be released.