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Exiguisphaera
From Fensome et al., 2019:
Exiguisphaera, Duxbury, 1979a, p.198–199.
Emendation: Jan du Chêne et al., 1986b, p.11.
Type: Duxbury, 1979a, pl.2, figs.2–3; text-figs.1A–B, as Exiguisphaera phragma.
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Original description: [Duxbury, 1979]:
Description:
Small, spheroidal dinoflagellate cysts having a minutely perforate body wall. The reflected tabulation pattern, ?a.cl., 4`, 6", ?c, 6```, 1p, ?1p.v., 1````, is outlined by rows of short, simple spines distally connected by trabeculae, which give each crest a fencelike appearance. A few small, intratabular spines may be present. The archeopyle is precingular, formed by detachment of plates 3" and 4````.
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Modified description:
Stover and Williams, 1987, p. 93:
Synopsis:
Cysts proximochorate, subspherical; gonyaulacacean paratabulation indicated by fence-like (perforate?) septa; paratabulation formula: 1pr, 3`,1a, 6", Xc, 6```,1p, 1````, ?1s; precingular 2P archeopyle formed by loss of paraplates 3" and 4", operculum free.
Description:
Shape: Subspherical.
Wall relationships: Autophragm only.
Wall features: Parasutural features consist of fencelike (perforate?) septa; spines may be present between parasutural features.
Archaeopyle: Precingular type 2P, (3" and 4"); opercular pieces free.
Paratabulation: Indicated by parasutural features; gonyaulacacean, formula: 1pr, 3`,1a, 6", Xc, 6```, 1p, 1````, and ?ps.
Paracingulum: Indicated by parallel, transverse septa; undivided.
Parasulcus: Longitudinally elongate area mainly on the hypocyst and bounded by parasutural features.
Size: Small to intermediate; about 40 to 55 µm.
Affinities:
Exiguisphaera differs from Occisucysta Gitmez 1970, which also has a precingular 2P archeopyle, by having paraplates 3" and 4" released during archeopyle formation rather than 2" and 3". The 2P archeopyle also serves to separate Exiguisphaera from several other genera (e.g. Leptodinium Klement 1960 emended Stover and Evitt 1978, and Rhynchodiniopsis Deflandre 1935 emended Sarjeant, 1982), with a gonyaulacacean paratabulation expressed by parasutural features, and which have type P (3" only) archeopyles.
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Emended description:
Jan du Chêne et al., 1986: (Translation: Fensome et al., 1991, p. 213-214):
Description:
Shape: Cyst proximate to proximochorate, subspherical in shape, without a prominent apical protrusion.
Cyst wall: Autophragm only.
Characters of the wall: The autophragm is often vacuolated. The parasutures are well marked by alignments of arches linked to each other distally. Intratabular ornament is absent or consists of elements of low relief, regularly or irregularly distributed, such as spines, baculae, verrucae, etc.
Paratabulation: Indicated by parasutural septa which delimit the following paraplates: 1-?pr, 4`, 6``, 6c, 5-6s, 6```, 1p, 1````. The scheme formed by these paraplates is of the gonyaulacoid type.
Archaeopyle: 2P (3``+4``). The operculum is free, compound.
Paracingulum: Composed of 6 cingular paraplates, it is generally well delineated by parasutural septa.
Parasulcus: Oriented longitudinally, it comprises five or six paraplates.
Affinities:
Exiguisphaera differs from Diacanthum Habib, 1972; emend. Habib and Drugg (1987) in the structure of the parasutural septa, typically formed by the alignment of arches. Furthermore, the archaeopyle in Exiguisphaera is formed by the loss of paraplates 3`` and 4`` only.
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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.
Exiguisphaera Duxbury, 1979a, emend. Jan du Chêne et al., 1986b, is a proximate, subspherical cyst, with the tabulation indicated by fence-like (perforate) septa. The gonyaulacoid tabulation is ?1-2pr, 4`, 6", 6c, 6"', 1p, 1"'', xs. The precingular archeopyle is formed from the loss of plates 3" and 4". The operculum is solvate, secate.
Exiguisphaera, Duxbury, 1979a, p.198–199.
Emendation: Jan du Chêne et al., 1986b, p.11.
Type: Duxbury, 1979a, pl.2, figs.2–3; text-figs.1A–B, as Exiguisphaera phragma.
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Duxbury, 1979]:
Description:
Small, spheroidal dinoflagellate cysts having a minutely perforate body wall. The reflected tabulation pattern, ?a.cl., 4`, 6", ?c, 6```, 1p, ?1p.v., 1````, is outlined by rows of short, simple spines distally connected by trabeculae, which give each crest a fencelike appearance. A few small, intratabular spines may be present. The archeopyle is precingular, formed by detachment of plates 3" and 4````.
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Modified description:
Stover and Williams, 1987, p. 93:
Synopsis:
Cysts proximochorate, subspherical; gonyaulacacean paratabulation indicated by fence-like (perforate?) septa; paratabulation formula: 1pr, 3`,1a, 6", Xc, 6```,1p, 1````, ?1s; precingular 2P archeopyle formed by loss of paraplates 3" and 4", operculum free.
Description:
Shape: Subspherical.
Wall relationships: Autophragm only.
Wall features: Parasutural features consist of fencelike (perforate?) septa; spines may be present between parasutural features.
Archaeopyle: Precingular type 2P, (3" and 4"); opercular pieces free.
Paratabulation: Indicated by parasutural features; gonyaulacacean, formula: 1pr, 3`,1a, 6", Xc, 6```, 1p, 1````, and ?ps.
Paracingulum: Indicated by parallel, transverse septa; undivided.
Parasulcus: Longitudinally elongate area mainly on the hypocyst and bounded by parasutural features.
Size: Small to intermediate; about 40 to 55 µm.
Affinities:
Exiguisphaera differs from Occisucysta Gitmez 1970, which also has a precingular 2P archeopyle, by having paraplates 3" and 4" released during archeopyle formation rather than 2" and 3". The 2P archeopyle also serves to separate Exiguisphaera from several other genera (e.g. Leptodinium Klement 1960 emended Stover and Evitt 1978, and Rhynchodiniopsis Deflandre 1935 emended Sarjeant, 1982), with a gonyaulacacean paratabulation expressed by parasutural features, and which have type P (3" only) archeopyles.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Emended description:
Jan du Chêne et al., 1986: (Translation: Fensome et al., 1991, p. 213-214):
Description:
Shape: Cyst proximate to proximochorate, subspherical in shape, without a prominent apical protrusion.
Cyst wall: Autophragm only.
Characters of the wall: The autophragm is often vacuolated. The parasutures are well marked by alignments of arches linked to each other distally. Intratabular ornament is absent or consists of elements of low relief, regularly or irregularly distributed, such as spines, baculae, verrucae, etc.
Paratabulation: Indicated by parasutural septa which delimit the following paraplates: 1-?pr, 4`, 6``, 6c, 5-6s, 6```, 1p, 1````. The scheme formed by these paraplates is of the gonyaulacoid type.
Archaeopyle: 2P (3``+4``). The operculum is free, compound.
Paracingulum: Composed of 6 cingular paraplates, it is generally well delineated by parasutural septa.
Parasulcus: Oriented longitudinally, it comprises five or six paraplates.
Affinities:
Exiguisphaera differs from Diacanthum Habib, 1972; emend. Habib and Drugg (1987) in the structure of the parasutural septa, typically formed by the alignment of arches. Furthermore, the archaeopyle in Exiguisphaera is formed by the loss of paraplates 3`` and 4`` only.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Notes:
G.L. Williams short notes on species, Mesozoic-Cenozoic dinocyst course, Urbino, Italy, May 17-22, 1999 - LPP VIEWER CD-ROM 99.5.
Exiguisphaera Duxbury, 1979a, emend. Jan du Chêne et al., 1986b, is a proximate, subspherical cyst, with the tabulation indicated by fence-like (perforate) septa. The gonyaulacoid tabulation is ?1-2pr, 4`, 6", 6c, 6"', 1p, 1"'', xs. The precingular archeopyle is formed from the loss of plates 3" and 4". The operculum is solvate, secate.