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Xenascus
From Fensome et al., 2019:
Xenascus Cookson and Eisenack, 1969, p.7.
Emendations: Yun Hyesu, 1981, p.60; Stover and Helby, 1987a, p.128.
Taxonomic senior synonym: Phoberocysta, by implication in Davey and Verdier (1971, p.27), who considered the "type species" of Xenascus, Xenascus australensis, to be a taxonomic junior synonym of Hystrichosphaera (as Phoberocysta, now Xenascus) ceratioides -- however, Lentin and Williams (1973, p.143) retained Xenascus.
Type: Cookson and Eisenack, 1969, figs.1I–J, as Xenascus australensis.
Type species: Xenascus australensis, Cookson and Eisenack, 1969 (figs.1I–J)]
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Original description: [Cookson and Eisenack, 1969]:
Diagnosis:
Shell consisting of a relatively thick-walled central body circular to slightly oval in outline, and a thinner, completely separate investing layer, the space between them being widest in the antapical region. The outer layer bears appendages of variable size and shape. A large apical archaeopyle, somewhat angular in outline, is developed.
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Modified description:
Stover and Evitt 1978, p. 87-88:
Synopsis:
Cysts proximate to proximochorate, cornucavate; outline ceratioid; endocyst subspherical to ellipsoidal; periphragm forms one apical, one antapical, and one lateral horn (rarely) or two quite unequal ones; bases of horns characteristically wide except for smaller lateral one; periphragm with few to many irregularly distributed processes and/or small protrusions, which vary in size and shape; archeopyle apical, Type tA.
Description:
Shape: Ceratioid, with single apical and antapical horns and two lateral horns of unequal size and of different shape.
Wall relationships: Cysts cornucavate; endocyst subspherical to ellipsoidal; horns and processes collectively cover an appreciable area of the cyst surface.
Wall features: Parasutural features generally lacking. Apical, antapical, and smaller lateral horns cylindrical to conical with relatively wide bases. Larger lateral horn trapezoidal to inverted L-shaped with the longer arm directed posteriorly and more or less parallel to the longitudinal axis of the cyst. Base of larger horn extends across all or most of the lateral precingular area, all of the lateral paracingular area, and part of the lateral postcingular area; smaller horn arises near paracingulum. Surface between horns themselves smooth or with few to many processes or projections, which vary in size and shape.
Paratabulation: Indicated by archeopyle only.
Archeopyle: Apical, Type tA; principal archeopyle suture slightly angular; operculum free.
Paracingulum: Generally not indicated.
Parasulcus: Not indicated.
Size: Large.
Affinities:
The bases of the horns of Xenascus are wider than those of Phoberocysta and cover an appreciably greater portion of the cyst surface than those of Phoberocysta. In addition, the lateral horns on Xenascus differ from each other considerably in size and shape, whereas the comparable structures on Phoberocysta are more similar to each other.
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Emended descriptions:
Yun, 1981: (Translation: LPP):
Diagnosis:
This genus is characterized by large, more or less elongate triangular apical horn, antapical horn, lateral horn, as well as by spines or ridges, which are arranged on the central body in 5 longitudinal rows. An archaeopyle develops by loss of the apical cap, which has 4 paraplates.
Affinities:
This genus, with a single lateral horn, is distinguished from Phoberocysta, with two lateral horns, by its large, long horns and the spines, or ledges, which are arranged on the central body in longitudinal rows. Phoberocysta shows more or less equally sized thorns, which are irregularly scattered on the central body.
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Stover and Helby, 1987:
Synopsis:
Cysts proximochorate, cornucavate to circumcavate, usually with prominent apical and antapical pericoels; outline compressed ceratioid
with 1 apical, 1 antapical and 1 cingular horn; endocyst subspherical to ellipsoidal; periphragm with few to moderate numbers of low to moderate length spines and/or processes arranged more or less parasuturally; archeopyle apical, type ltA], parasulcal notch markedly offset.
Description:
Shape: Pericyst outline ceratloid with 3 prominent horns: 1 apical, 1 antapical and 1 cingular; general outline often interrupted by spines and processes; endocyst subspherical to ellipsoidal.
Wall relationships: Cysts circumcavate to cornucavate, apical and antapical pericoels commonly substantial, minor cavation may occur at the base of major processes, or along the base of ridges.
Wall features: Processes and spines of variable size, usually hollow, may be distally open or closed, often with parasutural or penitabular alignment and may coalesce along their bases to form irregular crests; major processes commonly gonal; parasutural ridges may be developed,
usually marginal to the paracingulum and on dorsal surface of precingular and postcingular paraplates and on the apical horn.
Archeopyle: Apical, type [tA], principal archeopyle suture zigzag with offset parasulcal notch. Operculum free.
Paratabulation: Indicated by parasutural and penitabular alignment of processes, by low ridges and occasional spinose septa, and by archeopyle.
Paratabulation most obvious on epicyst, formula: 4`, 6``; hypocyst paratabulation not determined.
Paracingulum: Indicated by postion of cingular horn, lineation of parasutural and or penitabular processes and often by ridges margining the paracingulum.
Parasulcus: Indicated anteriorly by the offset parasulcal notch, but otherwise poorly delimited.
Size: Intermediate to large.
Affinities:
The shape and available paraplate configuration of Xenascus indicate a close relationship with Pseudoceratium Gocht emend. Helby 1987, but the latter lacks the large periphragmal processes and has a wider range of cyst wall relationships. Odontochitina Deflandre emend. Davey 1970 closely resembles Xenascus, having a distinct ceratioid shape with a cornucavate cyst wall. Davey (1970 p.354) interpreted both hypocystal horns as antapical although this may refer to general location rather than paraplate association. Wall and Evitt (1975, p.31) suggested that the lateral horn of Odontochitina originates from the postcingular series, close to the paracingulum (equator). This interpretation is supported by illustrations of O.operculata (Wilson 1974, pl.6, fig.5,6) which indicate that the lateral horn arises from the paracingulum on the right side of the cyst. Below (1981, p.22) has implied a transitional relationship between Xenascus and Odontochitina. Xenascus is distinguished from Odontochitina by more extensive cavation (the former is at least laterally circumcavate, while the latter is distinctly, and almost exclusively cornucavate), size and nature of the processes (potentially comparable Odontochitina species bear generally homogeneous, small, closed, spinose processes while processes on the former genus are extremely variable, even on single specimens) and the cingular horn of Xenascus generally incorporates distinctive lateral projection and cavation which are not commonly encountered in the latter genus. Phoberocysta resembles Xenascus in having numerous, apparently parasutural processes but is distinguished by having 2 subsymmetrical cingular horns.
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Lentin and Williams, 1989, p. 389:
Remarks:
The original type species, X. australensis, was considered a jr. sun. of Phoberocysta ceratioides (Deflandre, 1937) Davey and Verdier, 1971 by Davey and Verdier, 1971. Lentin and Williams, 1973, concurred with this interpretation. However, they retained Xenascus as a separate genus, with X. ceratiodes as the type species.
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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:
Xenascus, Cookson and Eisenack, 1969, emend. Yun Hyesu, 1981, emend. Stover and Helby, 1987a. Synopsis from Stover and Helby (1987a, p.128), Cysts proximochorate, cornucavate to circumcavate, usually with prominent apical and antapical pericoels; outline compressed ceratioid with 1 apical, 1 antapical and 1 cingular horn; endocyst subspherical to ellipsoidal; periphragm with few to moderate numbers of low to moderate length spines and/or processes arranged more less parasuturally; archeopyle apical, type [tA], parasulcal notch markedly offset.
Xenascus Cookson and Eisenack, 1969, p.7.
Emendations: Yun Hyesu, 1981, p.60; Stover and Helby, 1987a, p.128.
Taxonomic senior synonym: Phoberocysta, by implication in Davey and Verdier (1971, p.27), who considered the "type species" of Xenascus, Xenascus australensis, to be a taxonomic junior synonym of Hystrichosphaera (as Phoberocysta, now Xenascus) ceratioides -- however, Lentin and Williams (1973, p.143) retained Xenascus.
Type: Cookson and Eisenack, 1969, figs.1I–J, as Xenascus australensis.
Type species: Xenascus australensis, Cookson and Eisenack, 1969 (figs.1I–J)]
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Original description: [Cookson and Eisenack, 1969]:
Diagnosis:
Shell consisting of a relatively thick-walled central body circular to slightly oval in outline, and a thinner, completely separate investing layer, the space between them being widest in the antapical region. The outer layer bears appendages of variable size and shape. A large apical archaeopyle, somewhat angular in outline, is developed.
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Modified description:
Stover and Evitt 1978, p. 87-88:
Synopsis:
Cysts proximate to proximochorate, cornucavate; outline ceratioid; endocyst subspherical to ellipsoidal; periphragm forms one apical, one antapical, and one lateral horn (rarely) or two quite unequal ones; bases of horns characteristically wide except for smaller lateral one; periphragm with few to many irregularly distributed processes and/or small protrusions, which vary in size and shape; archeopyle apical, Type tA.
Description:
Shape: Ceratioid, with single apical and antapical horns and two lateral horns of unequal size and of different shape.
Wall relationships: Cysts cornucavate; endocyst subspherical to ellipsoidal; horns and processes collectively cover an appreciable area of the cyst surface.
Wall features: Parasutural features generally lacking. Apical, antapical, and smaller lateral horns cylindrical to conical with relatively wide bases. Larger lateral horn trapezoidal to inverted L-shaped with the longer arm directed posteriorly and more or less parallel to the longitudinal axis of the cyst. Base of larger horn extends across all or most of the lateral precingular area, all of the lateral paracingular area, and part of the lateral postcingular area; smaller horn arises near paracingulum. Surface between horns themselves smooth or with few to many processes or projections, which vary in size and shape.
Paratabulation: Indicated by archeopyle only.
Archeopyle: Apical, Type tA; principal archeopyle suture slightly angular; operculum free.
Paracingulum: Generally not indicated.
Parasulcus: Not indicated.
Size: Large.
Affinities:
The bases of the horns of Xenascus are wider than those of Phoberocysta and cover an appreciably greater portion of the cyst surface than those of Phoberocysta. In addition, the lateral horns on Xenascus differ from each other considerably in size and shape, whereas the comparable structures on Phoberocysta are more similar to each other.
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Emended descriptions:
Yun, 1981: (Translation: LPP):
Diagnosis:
This genus is characterized by large, more or less elongate triangular apical horn, antapical horn, lateral horn, as well as by spines or ridges, which are arranged on the central body in 5 longitudinal rows. An archaeopyle develops by loss of the apical cap, which has 4 paraplates.
Affinities:
This genus, with a single lateral horn, is distinguished from Phoberocysta, with two lateral horns, by its large, long horns and the spines, or ledges, which are arranged on the central body in longitudinal rows. Phoberocysta shows more or less equally sized thorns, which are irregularly scattered on the central body.
-------------------------------------
Stover and Helby, 1987:
Synopsis:
Cysts proximochorate, cornucavate to circumcavate, usually with prominent apical and antapical pericoels; outline compressed ceratioid
with 1 apical, 1 antapical and 1 cingular horn; endocyst subspherical to ellipsoidal; periphragm with few to moderate numbers of low to moderate length spines and/or processes arranged more or less parasuturally; archeopyle apical, type ltA], parasulcal notch markedly offset.
Description:
Shape: Pericyst outline ceratloid with 3 prominent horns: 1 apical, 1 antapical and 1 cingular; general outline often interrupted by spines and processes; endocyst subspherical to ellipsoidal.
Wall relationships: Cysts circumcavate to cornucavate, apical and antapical pericoels commonly substantial, minor cavation may occur at the base of major processes, or along the base of ridges.
Wall features: Processes and spines of variable size, usually hollow, may be distally open or closed, often with parasutural or penitabular alignment and may coalesce along their bases to form irregular crests; major processes commonly gonal; parasutural ridges may be developed,
usually marginal to the paracingulum and on dorsal surface of precingular and postcingular paraplates and on the apical horn.
Archeopyle: Apical, type [tA], principal archeopyle suture zigzag with offset parasulcal notch. Operculum free.
Paratabulation: Indicated by parasutural and penitabular alignment of processes, by low ridges and occasional spinose septa, and by archeopyle.
Paratabulation most obvious on epicyst, formula: 4`, 6``; hypocyst paratabulation not determined.
Paracingulum: Indicated by postion of cingular horn, lineation of parasutural and or penitabular processes and often by ridges margining the paracingulum.
Parasulcus: Indicated anteriorly by the offset parasulcal notch, but otherwise poorly delimited.
Size: Intermediate to large.
Affinities:
The shape and available paraplate configuration of Xenascus indicate a close relationship with Pseudoceratium Gocht emend. Helby 1987, but the latter lacks the large periphragmal processes and has a wider range of cyst wall relationships. Odontochitina Deflandre emend. Davey 1970 closely resembles Xenascus, having a distinct ceratioid shape with a cornucavate cyst wall. Davey (1970 p.354) interpreted both hypocystal horns as antapical although this may refer to general location rather than paraplate association. Wall and Evitt (1975, p.31) suggested that the lateral horn of Odontochitina originates from the postcingular series, close to the paracingulum (equator). This interpretation is supported by illustrations of O.operculata (Wilson 1974, pl.6, fig.5,6) which indicate that the lateral horn arises from the paracingulum on the right side of the cyst. Below (1981, p.22) has implied a transitional relationship between Xenascus and Odontochitina. Xenascus is distinguished from Odontochitina by more extensive cavation (the former is at least laterally circumcavate, while the latter is distinctly, and almost exclusively cornucavate), size and nature of the processes (potentially comparable Odontochitina species bear generally homogeneous, small, closed, spinose processes while processes on the former genus are extremely variable, even on single specimens) and the cingular horn of Xenascus generally incorporates distinctive lateral projection and cavation which are not commonly encountered in the latter genus. Phoberocysta resembles Xenascus in having numerous, apparently parasutural processes but is distinguished by having 2 subsymmetrical cingular horns.
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Lentin and Williams, 1989, p. 389:
Remarks:
The original type species, X. australensis, was considered a jr. sun. of Phoberocysta ceratioides (Deflandre, 1937) Davey and Verdier, 1971 by Davey and Verdier, 1971. Lentin and Williams, 1973, concurred with this interpretation. However, they retained Xenascus as a separate genus, with X. ceratiodes as the type species.
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Notes:
G.L. Williams short notes on species, Mesozoic-Cenozoic dinocyst course, Urbino, Italy, May 17-22, 1999 - LPP VIEWER CD-ROM 99.5:
Xenascus, Cookson and Eisenack, 1969, emend. Yun Hyesu, 1981, emend. Stover and Helby, 1987a. Synopsis from Stover and Helby (1987a, p.128), Cysts proximochorate, cornucavate to circumcavate, usually with prominent apical and antapical pericoels; outline compressed ceratioid with 1 apical, 1 antapical and 1 cingular horn; endocyst subspherical to ellipsoidal; periphragm with few to moderate numbers of low to moderate length spines and/or processes arranged more less parasuturally; archeopyle apical, type [tA], parasulcal notch markedly offset.