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Circulodinium
From Fensome et al., 2019:
Circulodinium, Alberti, 1961, p.28.
Emendations: McLachlan et al., 2018, p.681–682; Fensome et al., 2019a, p.36.
Taxonomic senior synonyms: Canningia, according to Eisenack (1964, p.322) (not Millioud 1969, p.425 as indicated in Fensome and Williams 2004 -- see Fensome et al., 2019a, p.3 for discussion) -- however, Jansonius (1986, p.204) retained Circulodinium; Cyclonephelium, according to Davey (1978, p.894) and Fensome et al. (2009, p.24) -- however, Jansonius (1986, p.204) and McLachlan et al. (2018, p.681–682) retained Circulodinium. Duxbury (2002, p.78) considered that Circulodinium may be a taxonomic junior synonym of Tenua Eisenack.
Type: Alberti, 1961, pl.4, fig.20, as Circulodinium hirtellum.
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Original description: [Alberti, 1961]: (Translation: LPP):
Diagnosis:
Shell flattened to flat, in outline more or less circular to irregularly rounded. With a small, distally slightly blunted apical projection. Hypotheca indented antapically, producing two antapical bulges, one of which may be more or less reduced. Shell without transverse furrow, untabulated. Its surface, except for the dorsal and ventral centre and the antapical indentation, set with short, solid, partially distally widened in a paddle-shaped fashion, rarely furcate thorns.
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Emended description:
Jansonius, 1986
Diagnosis:
Proximate cysts, more or less dorso-ventrally flattened (lenticular or concavo-convex); outline subcircular to polygonal, commonly with a small apical prominence and one, or two unequal, antapical prominence(s), although the antapex may be rounded. Wall apparently single-layered, ornamented with free elements of varying length and shape, usually spines with capitate or bifurcate tips, in part distally broadened to a paddle shape, generally more strongly developed in peripheral regions, more or less strongly reduced in size and density in central ventral and dorsal regions.
Archeopyle apical, principal suture angled, accessory sutures lacking or short, operculum free or attached.
Paratabulation or cingulum generally not indicated; sulcal notch off-set to left.
Remarks:
When Cyclonephelium was proposed, Deflandre and Cookson (1955) assigned four species; of these, two were later transferred to Glaphyrocysta. C. compactum remains the nomenclatural type of the genus in a strict sense; C. distinctum is here transferred to Circulodinium. Since Sarjeant (1985) concluded that Tenua is a senior synonym of Cerbia, the genus Circulodinium now is the preferred receptacle for cysts of the general type of C. hirtellum, its nomenclatural type. In Sentusidinium there is no dorso-ventral flattening, no reduction of sculpture in the central regions, and the sulcal notch is not displaced toward the left. It is not clear why Sarjeant and Stover (1978) ignored the genus Circulodinium and its type species.
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Emended diagnosis Fensome et al., 2019a:
Type species. Circulodinium colliveri (Cookson & Eisenack, 1960, pl. 38, figs 3, 4) Helby, 1987.
Emended diagnosis. Areoligeracean cysts that are proximate, with circular to lenticular ambitus. Rounded to asymmetrical antapex and apical horn present. Acavate. Low-relief ornamentation of unit type, uniformly distributed,
granulate, denticulate, or vermiculate. Tabulation indicated by archaeopyle only. Archaeopyle apical, with formula A (1–4’) , operculum free; sulcal notch offset to the left.
Remarks. Most proximate to proximochorate acavate areoligeraceans are currently accommodated in the genera
Circulodinium and Cyclonephelium, the former generally with free-standing ornament and the latter with linear or
connected ornament. Circulodinium has also been used to encompass forms with no or low relief (Helby 1987), as
reflected in specimens from Hornby Island. As a concept, Circulodinium can be regarded as distinct based on limited
development and projection of surface ornament. The original type species, Circulodinium hirtellum, has since been
reinterpreted as a junior synonym of Cyclonephelium distinctum (Fensome et al. 2009). Therefore, we propose
Circulodinium colliveri as the type species in order to maintain validity of the genus.
Comparison. Circulodinium differs from Cyclonephelium in having surface features limited to granulate and denticulate
ornamentation and the absence of arranged process formation and trabecular connections. Circulodinium can also
be distinguished from Canninginopsis in lacking sutural alignment of granules and verrucae as well as possessing a uniform distribution of nontabulate sculptural elements on the autophragm.
Circulodinium, Alberti, 1961, p.28.
Emendations: McLachlan et al., 2018, p.681–682; Fensome et al., 2019a, p.36.
Taxonomic senior synonyms: Canningia, according to Eisenack (1964, p.322) (not Millioud 1969, p.425 as indicated in Fensome and Williams 2004 -- see Fensome et al., 2019a, p.3 for discussion) -- however, Jansonius (1986, p.204) retained Circulodinium; Cyclonephelium, according to Davey (1978, p.894) and Fensome et al. (2009, p.24) -- however, Jansonius (1986, p.204) and McLachlan et al. (2018, p.681–682) retained Circulodinium. Duxbury (2002, p.78) considered that Circulodinium may be a taxonomic junior synonym of Tenua Eisenack.
Type: Alberti, 1961, pl.4, fig.20, as Circulodinium hirtellum.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Alberti, 1961]: (Translation: LPP):
Diagnosis:
Shell flattened to flat, in outline more or less circular to irregularly rounded. With a small, distally slightly blunted apical projection. Hypotheca indented antapically, producing two antapical bulges, one of which may be more or less reduced. Shell without transverse furrow, untabulated. Its surface, except for the dorsal and ventral centre and the antapical indentation, set with short, solid, partially distally widened in a paddle-shaped fashion, rarely furcate thorns.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Emended description:
Jansonius, 1986
Diagnosis:
Proximate cysts, more or less dorso-ventrally flattened (lenticular or concavo-convex); outline subcircular to polygonal, commonly with a small apical prominence and one, or two unequal, antapical prominence(s), although the antapex may be rounded. Wall apparently single-layered, ornamented with free elements of varying length and shape, usually spines with capitate or bifurcate tips, in part distally broadened to a paddle shape, generally more strongly developed in peripheral regions, more or less strongly reduced in size and density in central ventral and dorsal regions.
Archeopyle apical, principal suture angled, accessory sutures lacking or short, operculum free or attached.
Paratabulation or cingulum generally not indicated; sulcal notch off-set to left.
Remarks:
When Cyclonephelium was proposed, Deflandre and Cookson (1955) assigned four species; of these, two were later transferred to Glaphyrocysta. C. compactum remains the nomenclatural type of the genus in a strict sense; C. distinctum is here transferred to Circulodinium. Since Sarjeant (1985) concluded that Tenua is a senior synonym of Cerbia, the genus Circulodinium now is the preferred receptacle for cysts of the general type of C. hirtellum, its nomenclatural type. In Sentusidinium there is no dorso-ventral flattening, no reduction of sculpture in the central regions, and the sulcal notch is not displaced toward the left. It is not clear why Sarjeant and Stover (1978) ignored the genus Circulodinium and its type species.
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Emended diagnosis Fensome et al., 2019a:
Type species. Circulodinium colliveri (Cookson & Eisenack, 1960, pl. 38, figs 3, 4) Helby, 1987.
Emended diagnosis. Areoligeracean cysts that are proximate, with circular to lenticular ambitus. Rounded to asymmetrical antapex and apical horn present. Acavate. Low-relief ornamentation of unit type, uniformly distributed,
granulate, denticulate, or vermiculate. Tabulation indicated by archaeopyle only. Archaeopyle apical, with formula A (1–4’) , operculum free; sulcal notch offset to the left.
Remarks. Most proximate to proximochorate acavate areoligeraceans are currently accommodated in the genera
Circulodinium and Cyclonephelium, the former generally with free-standing ornament and the latter with linear or
connected ornament. Circulodinium has also been used to encompass forms with no or low relief (Helby 1987), as
reflected in specimens from Hornby Island. As a concept, Circulodinium can be regarded as distinct based on limited
development and projection of surface ornament. The original type species, Circulodinium hirtellum, has since been
reinterpreted as a junior synonym of Cyclonephelium distinctum (Fensome et al. 2009). Therefore, we propose
Circulodinium colliveri as the type species in order to maintain validity of the genus.
Comparison. Circulodinium differs from Cyclonephelium in having surface features limited to granulate and denticulate
ornamentation and the absence of arranged process formation and trabecular connections. Circulodinium can also
be distinguished from Canninginopsis in lacking sutural alignment of granules and verrucae as well as possessing a uniform distribution of nontabulate sculptural elements on the autophragm.