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Exochosphaeridium
From Fensome et al., 2019:
Exochosphaeridium, Davey et al., 1966, p.165.
Emendation: Helenes, 2000, p.137.
Type: Davey et al., 1966, pl.2, figs.9–10, as Exochosphaeridium phragmites.
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Original description: [Davey et al., 1966]:
Diagnosis:
Subspherical chorate cysts bearing numerous, commonly simple, closed processes.
Apical process larger than normal processes and irregularly branched.
Archaeopyle precingular.
Remarks:
The processes are commonly acuminate, often joining proximally, but may be branched. Only rarely can an alignment of these processes be observed. The apical process makes orientation easy and indicates that the archaeopyle is precingular. Detached archaeopyle plates have been found and these show the characteristic precingular shape.
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Modified description:
Stover and Evitt 1978, p. 154:
Synopsis:
Cysts skolochorate; body spherical with numerous nontabular, simple or branched, fibrous, typically solid processes; apical and occasionally, antapical processes wider, longer, or more irregularly branched than others; archeopyle precingular, Type P.
Description:
Shape: Body subspherical.
Wall relationships: Usually autophragm only; occasionally endophragm and periphragm discernible at the bases of processes.
Wall features: No parasutural features. Nontabular processes, simple or branched, solid, fibrous, tips acuminate or expanded distally; apical process and, less commonly, the antapical process may be wider, longer, or more irregularly branched than other processes. Surface between processes fibrous.
Paratabulation: Indicated by archeopyle only.
Archeopyle: Precingular, Type P (3`` only); operculum free.
Paracingulum: Not indicated, or indicated weakly by transverse alignment of some processes.
Parasulcus: Not indicated.
Size: Intermediate.
Affinities:
Exochosphaeridium differs from Amphorosphaeridium in having solid, less complexly branched processes, except for generally wider or longer apical process. It differs from Operculodinium in having fibrous processes and a different apical process, which Operculodinium lacks. Retention of both Exochosphaeridium and Amphorosphaeridium seem dubious.
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Emended description:
Helenes, 2000:
Diagnosis:
Ovoid, chorate, uncompressed acavate cysts, commonly with a weakly developed apical horn. Processes nontabular to less commonly intratabular. Precingular archeopyle type P. When discernible, the dorsal tabulation shows dextral torsion, with postcingular parasuture IV/V (Kofoid 3"'/4"') approximately middorsal n position: the antapical Y plate (Kofoid 1"") is asymmetrical, and the ventral area shows an A/ai contact (Kofoid 4'/as).
Description:
Shape: Chorate cyst with ovoid central body, and a poorly developed apical horn. Cingular cross-section is usually circular, with a slight indentation in the sulcal area.
Size: Small to intermediate
Wall structure: Acavate
Archeopyle: Precingular archeopyle, Type P4 (i.e. mid-dorsal paraplate 4, Kofoid 3"). Operculum usually slightly reduced, and free.
Paratabulation: Usually not discernible. When visible, intratabular processes define the following paraplates (text-figure 2-A): two poorly defined preapicals; P and Q (1 pr and 2 pr), four apicals: A, B, C, and 1u (1', 2', 3', and 4'), six precingulars: 2,3,4,5,6 and 1i (1", 2", 3", 4", 5" and 6"), six poorly defined cingulars: au, b, c, d, e, and fi (1c, 2c, 3c, 4c, 5c, and 6c), five postcingulars: II, III, IV, V, and VI (2"'. 3"'. 4"'. 5"'. and 6"'), six poorly defined sulcals: ai, fu, li?, lm?, Iu?, and Z (as, ras, rs, 1"' and ps), one posterior intercalary: X (1p), and one antapical: Y (1"").
The paratabulation pattern is characterized by a symmetrical antapical arrangement: the postcingular contact IV/V (4"'/5"') is usually middorsal, located to the left of precingular 4/5 (3"'/4"), indicating a dextral torsion of the hypocyst. S-type sulcus with an A/ai vental arrangement: paraplate A (4') is six-sided and contacts: Q, C, 6, 1i, ai and 1u (2pr, 3', 5", as and 1'). No anterior intercalary paraplates. Apical arrangement, probably Q/B, although this feature has been difficult to ascertain. The P (1pr) structure is represented by a spine at the tip of the apical horn.
Remarks:
Species in this genus differ from one another mainly by the height and shape of the processes or spines, and degree of development of the apical structure. Most species show non-tabular arrangement of the processes, although occasionally some forms show intratabular clustering.
(See Helens, 2000 for a discussion on the suprageneric assignment of this genus.)
Exochosphaeridium, Davey et al., 1966, p.165.
Emendation: Helenes, 2000, p.137.
Type: Davey et al., 1966, pl.2, figs.9–10, as Exochosphaeridium phragmites.
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Davey et al., 1966]:
Diagnosis:
Subspherical chorate cysts bearing numerous, commonly simple, closed processes.
Apical process larger than normal processes and irregularly branched.
Archaeopyle precingular.
Remarks:
The processes are commonly acuminate, often joining proximally, but may be branched. Only rarely can an alignment of these processes be observed. The apical process makes orientation easy and indicates that the archaeopyle is precingular. Detached archaeopyle plates have been found and these show the characteristic precingular shape.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Modified description:
Stover and Evitt 1978, p. 154:
Synopsis:
Cysts skolochorate; body spherical with numerous nontabular, simple or branched, fibrous, typically solid processes; apical and occasionally, antapical processes wider, longer, or more irregularly branched than others; archeopyle precingular, Type P.
Description:
Shape: Body subspherical.
Wall relationships: Usually autophragm only; occasionally endophragm and periphragm discernible at the bases of processes.
Wall features: No parasutural features. Nontabular processes, simple or branched, solid, fibrous, tips acuminate or expanded distally; apical process and, less commonly, the antapical process may be wider, longer, or more irregularly branched than other processes. Surface between processes fibrous.
Paratabulation: Indicated by archeopyle only.
Archeopyle: Precingular, Type P (3`` only); operculum free.
Paracingulum: Not indicated, or indicated weakly by transverse alignment of some processes.
Parasulcus: Not indicated.
Size: Intermediate.
Affinities:
Exochosphaeridium differs from Amphorosphaeridium in having solid, less complexly branched processes, except for generally wider or longer apical process. It differs from Operculodinium in having fibrous processes and a different apical process, which Operculodinium lacks. Retention of both Exochosphaeridium and Amphorosphaeridium seem dubious.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Emended description:
Helenes, 2000:
Diagnosis:
Ovoid, chorate, uncompressed acavate cysts, commonly with a weakly developed apical horn. Processes nontabular to less commonly intratabular. Precingular archeopyle type P. When discernible, the dorsal tabulation shows dextral torsion, with postcingular parasuture IV/V (Kofoid 3"'/4"') approximately middorsal n position: the antapical Y plate (Kofoid 1"") is asymmetrical, and the ventral area shows an A/ai contact (Kofoid 4'/as).
Description:
Shape: Chorate cyst with ovoid central body, and a poorly developed apical horn. Cingular cross-section is usually circular, with a slight indentation in the sulcal area.
Size: Small to intermediate
Wall structure: Acavate
Archeopyle: Precingular archeopyle, Type P4 (i.e. mid-dorsal paraplate 4, Kofoid 3"). Operculum usually slightly reduced, and free.
Paratabulation: Usually not discernible. When visible, intratabular processes define the following paraplates (text-figure 2-A): two poorly defined preapicals; P and Q (1 pr and 2 pr), four apicals: A, B, C, and 1u (1', 2', 3', and 4'), six precingulars: 2,3,4,5,6 and 1i (1", 2", 3", 4", 5" and 6"), six poorly defined cingulars: au, b, c, d, e, and fi (1c, 2c, 3c, 4c, 5c, and 6c), five postcingulars: II, III, IV, V, and VI (2"'. 3"'. 4"'. 5"'. and 6"'), six poorly defined sulcals: ai, fu, li?, lm?, Iu?, and Z (as, ras, rs, 1"' and ps), one posterior intercalary: X (1p), and one antapical: Y (1"").
The paratabulation pattern is characterized by a symmetrical antapical arrangement: the postcingular contact IV/V (4"'/5"') is usually middorsal, located to the left of precingular 4/5 (3"'/4"), indicating a dextral torsion of the hypocyst. S-type sulcus with an A/ai vental arrangement: paraplate A (4') is six-sided and contacts: Q, C, 6, 1i, ai and 1u (2pr, 3', 5", as and 1'). No anterior intercalary paraplates. Apical arrangement, probably Q/B, although this feature has been difficult to ascertain. The P (1pr) structure is represented by a spine at the tip of the apical horn.
Remarks:
Species in this genus differ from one another mainly by the height and shape of the processes or spines, and degree of development of the apical structure. Most species show non-tabular arrangement of the processes, although occasionally some forms show intratabular clustering.
(See Helens, 2000 for a discussion on the suprageneric assignment of this genus.)