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Liasidium
From Fensome et al., 2019:
Liasidium, Drugg, 1978, p.69.
Taxonomic junior synonym: Liassogonyaulax (name not validly published), by implication in Brittain et al. (2010, p.72).
Type: Drugg, 1978, pl.5, fig.9, as Liasidium variabile.
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Original description: [Drugg, 1978]:
Description:
Cyst polygonal to broadly spindle-shaped in outline. Slightly helicoidal paracingulum clearly delineated. Archeopyle large and intercalary. Apical and antapical horns always present although the latter is variable in development. Often a second rudimentary antapical horn is also present. Paratabulation generally absent. Endocyst absent.
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Modified description:
Stover and Williams, 1987, p. 149:
Synopsis:
Cysts proximate, outline in dorsal-ventral view polygonal, but more commonly broadly spindle-shaped; prominent apical and right antapical horns present, left antapical horn reduced or absent; autophragm chagreenate to striate; paratabulation indicated by paracingulum and archeopyle, latter intercalary, type uncertain (type I or 3I) or possibly combined apical and intercalary (type Al or tAI); operculum free.
Description:
Shape: Outline in dorsal-ventral view polygonal to spindle-shaped. Shape depends on degree of development of horns and anterior "shoulders". Apical and right antapical horns characteristically prominent, left antapical horn undeveloped or reduced.
Wall relationships: Autophragm only.
Wall features: No parasutural features. Wall chagreenate to striate, striations occur most commonly on horns.
Archeopyle: Probably intercalary, type I (2a), but size and shape (anteriorly and posteriorly rectilinear) of the opening on some specimens suggests that it may be type 3I (1a-3a). Also, if the anterior archeopyle margin is camerate, one apical paraplate (3`?) may be involved; operculum free, isolated opercula not observed.
Paratabulation: Indicated by archeopyle and paracingulum.
Paracingulum: Indicated by parallel, transverse, low ridges; undivided, ventral ends offset slightly.
Parasulcus: Vaguely indicated on hypocyst by a shallow depression.
Size: Small to large, length from about 35 to 120 µm.
Affinities:
The more polygonal-shaped forms of Liasidium with well defined "shoulders" are similar to Chatangiella Vozzhennikova 1967 emended Lentin and Williams 1976. However, the latter is cavate, generally has a proportionately shorter apical horn, and commonly has indications of paratabulation other than the archeopyle and paracingulum. Diconodinium Eisenack and Cookson 1960 emended Morgan 1977 differs from the more spindle-shaped variants of Liasidium in possessing a proportionately smaller archeopyle and in having the single antapical horn.
Liasidium, Drugg, 1978, p.69.
Taxonomic junior synonym: Liassogonyaulax (name not validly published), by implication in Brittain et al. (2010, p.72).
Type: Drugg, 1978, pl.5, fig.9, as Liasidium variabile.
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Drugg, 1978]:
Description:
Cyst polygonal to broadly spindle-shaped in outline. Slightly helicoidal paracingulum clearly delineated. Archeopyle large and intercalary. Apical and antapical horns always present although the latter is variable in development. Often a second rudimentary antapical horn is also present. Paratabulation generally absent. Endocyst absent.
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Modified description:
Stover and Williams, 1987, p. 149:
Synopsis:
Cysts proximate, outline in dorsal-ventral view polygonal, but more commonly broadly spindle-shaped; prominent apical and right antapical horns present, left antapical horn reduced or absent; autophragm chagreenate to striate; paratabulation indicated by paracingulum and archeopyle, latter intercalary, type uncertain (type I or 3I) or possibly combined apical and intercalary (type Al or tAI); operculum free.
Description:
Shape: Outline in dorsal-ventral view polygonal to spindle-shaped. Shape depends on degree of development of horns and anterior "shoulders". Apical and right antapical horns characteristically prominent, left antapical horn undeveloped or reduced.
Wall relationships: Autophragm only.
Wall features: No parasutural features. Wall chagreenate to striate, striations occur most commonly on horns.
Archeopyle: Probably intercalary, type I (2a), but size and shape (anteriorly and posteriorly rectilinear) of the opening on some specimens suggests that it may be type 3I (1a-3a). Also, if the anterior archeopyle margin is camerate, one apical paraplate (3`?) may be involved; operculum free, isolated opercula not observed.
Paratabulation: Indicated by archeopyle and paracingulum.
Paracingulum: Indicated by parallel, transverse, low ridges; undivided, ventral ends offset slightly.
Parasulcus: Vaguely indicated on hypocyst by a shallow depression.
Size: Small to large, length from about 35 to 120 µm.
Affinities:
The more polygonal-shaped forms of Liasidium with well defined "shoulders" are similar to Chatangiella Vozzhennikova 1967 emended Lentin and Williams 1976. However, the latter is cavate, generally has a proportionately shorter apical horn, and commonly has indications of paratabulation other than the archeopyle and paracingulum. Diconodinium Eisenack and Cookson 1960 emended Morgan 1977 differs from the more spindle-shaped variants of Liasidium in possessing a proportionately smaller archeopyle and in having the single antapical horn.