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Belowia
From Williams et al., 2017:
[Belowia, Riding and Helby, 2001g, p. 189, 191, 193.
Type species: Belowia balteus, Riding and Helby, 2001g (figs.6A–C)
Age: Tithonian]
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Original descriptions: [Riding and Helby, 2001g]:
Diagnosis:
Intermediate to large dinoflagellate cysts, which vary from proximate to chorate. The subspherical to ellipsoidal cyst body is markedly indented at the parasulcus. A hollow ectophragmal projection occurs at the paracingulum. The hypocyst commonly bears a further ectophragmal development which, in most cases, encompasses the major processes, where developed. This hypocystal ectophragm is highly variable: in the chorate forms, it may be virtually absent and the major hypocystal processes may be well developed. The paratabulation is standard gonyaulacalean, indicated by the intratabular postcingular processes, where developed, and the principal archaeopyle suture. Archaeopyle apical; operculum free.
Remarks:
Belowia is a morphologically complex and unusual genus; Figs. 5 to 8 illustrate the principal features. It is ellipsoidal to subcircular polar outline has an apical archaeopyle. The cyst wall comprises autophragm and ectophragm. The ectophragm separates from the autophragm on the posterior part of the precingular paraplate series. Major processes in the postcingular paraplate series may support and/or may be incorporated into the hypocystal ectophragm. Numerous trabecular processes also emerge from the vicinity of the anterior and posterior paracingular parasutures to form a hollow paracingular ectophragmal tunnel, which is interrupted at the parasulcus.
Affinities:
The Kimmeridgian-Tithonian genus Hadriana Riding & Helby (this volume) is very similar to Belowia. They both have a small, essentially smooth epicyst, devoid of processes, and wall separation occurring close to the posterior limits of the precingular paraplates. Although there are marked hypocystal differences, both genera display major ectophragmal development at and below the paracingulum. However, Hadriana lacks a paracingular tunnel, large processes and the ectophragm is widely open antapically (the opening is about twice the autocyst diameter). Stephodinium Deflandre 1939 emend. Davey 1970 is characterised by an inflated paracingular periphragmal protrusions. It is distinguished form Belowia by having a cavate wall relationships, a precingular archaeopyle and by lacking trabeculate ectophragmal processes. Belowia differs from trabeculate chorate dinoflagellate cyst genera like Adnatosphaeridium William & Downie 1966, Hapsidaulax Sarjeant 1975, Hystrichosphaeria Alberti 1961 and Rigaudella Below 1982 in having a distinctive ectophragmal tunnel along the paracingulum and in lacking intratabular processes in the apical and precingular paraplate series. Balteocysta Stover & Evitt 1978 has a subspherical cyst body and an ectophragm which is confined to the paracingular region.
[Belowia, Riding and Helby, 2001g, p. 189, 191, 193.
Type species: Belowia balteus, Riding and Helby, 2001g (figs.6A–C)
Age: Tithonian]
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original descriptions: [Riding and Helby, 2001g]:
Diagnosis:
Intermediate to large dinoflagellate cysts, which vary from proximate to chorate. The subspherical to ellipsoidal cyst body is markedly indented at the parasulcus. A hollow ectophragmal projection occurs at the paracingulum. The hypocyst commonly bears a further ectophragmal development which, in most cases, encompasses the major processes, where developed. This hypocystal ectophragm is highly variable: in the chorate forms, it may be virtually absent and the major hypocystal processes may be well developed. The paratabulation is standard gonyaulacalean, indicated by the intratabular postcingular processes, where developed, and the principal archaeopyle suture. Archaeopyle apical; operculum free.
Remarks:
Belowia is a morphologically complex and unusual genus; Figs. 5 to 8 illustrate the principal features. It is ellipsoidal to subcircular polar outline has an apical archaeopyle. The cyst wall comprises autophragm and ectophragm. The ectophragm separates from the autophragm on the posterior part of the precingular paraplate series. Major processes in the postcingular paraplate series may support and/or may be incorporated into the hypocystal ectophragm. Numerous trabecular processes also emerge from the vicinity of the anterior and posterior paracingular parasutures to form a hollow paracingular ectophragmal tunnel, which is interrupted at the parasulcus.
Affinities:
The Kimmeridgian-Tithonian genus Hadriana Riding & Helby (this volume) is very similar to Belowia. They both have a small, essentially smooth epicyst, devoid of processes, and wall separation occurring close to the posterior limits of the precingular paraplates. Although there are marked hypocystal differences, both genera display major ectophragmal development at and below the paracingulum. However, Hadriana lacks a paracingular tunnel, large processes and the ectophragm is widely open antapically (the opening is about twice the autocyst diameter). Stephodinium Deflandre 1939 emend. Davey 1970 is characterised by an inflated paracingular periphragmal protrusions. It is distinguished form Belowia by having a cavate wall relationships, a precingular archaeopyle and by lacking trabeculate ectophragmal processes. Belowia differs from trabeculate chorate dinoflagellate cyst genera like Adnatosphaeridium William & Downie 1966, Hapsidaulax Sarjeant 1975, Hystrichosphaeria Alberti 1961 and Rigaudella Below 1982 in having a distinctive ectophragmal tunnel along the paracingulum and in lacking intratabular processes in the apical and precingular paraplate series. Balteocysta Stover & Evitt 1978 has a subspherical cyst body and an ectophragm which is confined to the paracingular region.