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Charlesdowniea
From Fensome et al., 2019:
Charlesdowniea, Lentin and Vozzhennikova, 1989, p.225,227.
Emendation: Williams et al., 2015, p.302.
Type: Williams and Downie, 1966b, pl.18, fig.8; text-fig.47, as Wetzeliella coleothrypta.
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Original description: [Lentin and Vozzhennikova, 1989]:
Diagnosis:
Dorso-ventrally compressed peridinioid cysts with one apical, two lateral and two antapical horns, the right of which may be reduced; circumcavate to cornucavate; endocyst broadly elliptical to round in outline; ectophragm incomplete, present over some or all intratabular areas and consistently absent over pandasutural areas. Endophragm smooth or lightly ornamented with features of low relief; periphragm ornamented with smooth tubular or solid processes arranged in intratabular clusters; processes may be reduced or absent on the mid-dorsal and/or mid-ventral surfaces. Pandasutural areas smooth to faintly ornamented. Ectophragm smooth, perforate, faintly ornamented or consisting of an open reticulum of trabeculae.
Paratabulation indicated on the periphragm by intratabular processes and pandasutural zones without processes and by the shape of the ectophragm pieces whose outline tends to approximate the shape of the underlying paraplate; peridiniacean, formula 4`, 3a, 7``, Xc or 5c, 5````, 2````, 0s or 2-4s.
Archeopyle Type I/I (quadra 2a only), operculum free or attached.
Paracingulum indicated by the location of the lateral horns and/or transverse alignment of processes on the dorsal and ventral surfaces, and/or fine rectilinear intratabular groups of processes.
Parasulcus not indicated or indicated by a shallow depression which may or may not have intratabular clusters of processes.
Affinities:
All of the species included in Charlesdowniea were previously assigned to the genus Kisselovia sensu Lentin and Williams and bear little resemblance to Kisselovia sensu stricto. Charlesdowneia differs from Kisselovia in the presence of processes on the periphragm which are connected distally to form an ectophragm. It is considered that the presence or absence of a soleiform archeopyle in this group of fossils is not a generic characteristic and is indeed variable even within the species.
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Emended description:
Williams et al., 2015:
Diagnosis:
Wetzelielloidean cysts with an equiepeliform archeopyle and pericyst with processes distally united by ectophragmal membranes.
Description:
Shape: Dorso-ventral outline of pericyst rhomboidal, horns moderately well developed. Dorso-ventral outline of endocyst rounded to quadrate.
Wall structure: Periphragm thin, with penitabular processes or clusters of intratabular processes; processes distally connected by an ectophragm. Endophragm thin, smooth to granular.
Pericoels: Cysts circumcavate to cornucavate.
Tabulation: Partially to completely delineated by processes and an ectophragm that is generally intratabular, but that can be restricted to penitabular areas.
Archeopyle: Equiepeliform, Periarcheopyle with no or minimal extension into apical pericoel, operculum free. Endoarcheopyle of same size or smaller than periarcheopyle, operculum free.
Furrows. Cingulum and sulcus variably to completely expressed by membranes supported by processes, or not delineated at all. Where developed, processes delineating cingulum are confined to a single row.
Dimensions:
Size: Large.
The holotype of Charlesdowniea coleothrypta has a pericyst length of 122 μm and a width of 110 μm; the endocyst length is 69 μm and the width is 62 μm.
Affinities and Discussion:
The membranous ectophragm uniting the processes distally is extremely variable in its distribution. In some species, such as Charlesdowniea coleothrypta, the membrane is clearly intratabular but mirrors plate boundaries. In others, such as Charlesdowniea edwardsii, the processes and the interconnected membranes are largely restricted to the ambital region. Other genera besides Charlesdowniea possessing an equiepeliform archeopyle are Apectodinium, Axiodinium, Epelidinium, Sophismatia and Vallodinium. Apectodinium and Axiodinium have processes that are distally free; Epelidinium has a pericyst surface that is smooth or ornamented with features of low relief; Sophismatia is characterised by processes joined by trabecula; and Vallodinium has sutural to penitabular ornamentation on the pericyst. Piladinium and Talladinium also have a membranous ectophragm, but have latiepeliform and soleiform archeopyles respectively.
Charlesdowniea, Lentin and Vozzhennikova, 1989, p.225,227.
Emendation: Williams et al., 2015, p.302.
Type: Williams and Downie, 1966b, pl.18, fig.8; text-fig.47, as Wetzeliella coleothrypta.
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Lentin and Vozzhennikova, 1989]:
Diagnosis:
Dorso-ventrally compressed peridinioid cysts with one apical, two lateral and two antapical horns, the right of which may be reduced; circumcavate to cornucavate; endocyst broadly elliptical to round in outline; ectophragm incomplete, present over some or all intratabular areas and consistently absent over pandasutural areas. Endophragm smooth or lightly ornamented with features of low relief; periphragm ornamented with smooth tubular or solid processes arranged in intratabular clusters; processes may be reduced or absent on the mid-dorsal and/or mid-ventral surfaces. Pandasutural areas smooth to faintly ornamented. Ectophragm smooth, perforate, faintly ornamented or consisting of an open reticulum of trabeculae.
Paratabulation indicated on the periphragm by intratabular processes and pandasutural zones without processes and by the shape of the ectophragm pieces whose outline tends to approximate the shape of the underlying paraplate; peridiniacean, formula 4`, 3a, 7``, Xc or 5c, 5````, 2````, 0s or 2-4s.
Archeopyle Type I/I (quadra 2a only), operculum free or attached.
Paracingulum indicated by the location of the lateral horns and/or transverse alignment of processes on the dorsal and ventral surfaces, and/or fine rectilinear intratabular groups of processes.
Parasulcus not indicated or indicated by a shallow depression which may or may not have intratabular clusters of processes.
Affinities:
All of the species included in Charlesdowniea were previously assigned to the genus Kisselovia sensu Lentin and Williams and bear little resemblance to Kisselovia sensu stricto. Charlesdowneia differs from Kisselovia in the presence of processes on the periphragm which are connected distally to form an ectophragm. It is considered that the presence or absence of a soleiform archeopyle in this group of fossils is not a generic characteristic and is indeed variable even within the species.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Emended description:
Williams et al., 2015:
Diagnosis:
Wetzelielloidean cysts with an equiepeliform archeopyle and pericyst with processes distally united by ectophragmal membranes.
Description:
Shape: Dorso-ventral outline of pericyst rhomboidal, horns moderately well developed. Dorso-ventral outline of endocyst rounded to quadrate.
Wall structure: Periphragm thin, with penitabular processes or clusters of intratabular processes; processes distally connected by an ectophragm. Endophragm thin, smooth to granular.
Pericoels: Cysts circumcavate to cornucavate.
Tabulation: Partially to completely delineated by processes and an ectophragm that is generally intratabular, but that can be restricted to penitabular areas.
Archeopyle: Equiepeliform, Periarcheopyle with no or minimal extension into apical pericoel, operculum free. Endoarcheopyle of same size or smaller than periarcheopyle, operculum free.
Furrows. Cingulum and sulcus variably to completely expressed by membranes supported by processes, or not delineated at all. Where developed, processes delineating cingulum are confined to a single row.
Dimensions:
Size: Large.
The holotype of Charlesdowniea coleothrypta has a pericyst length of 122 μm and a width of 110 μm; the endocyst length is 69 μm and the width is 62 μm.
Affinities and Discussion:
The membranous ectophragm uniting the processes distally is extremely variable in its distribution. In some species, such as Charlesdowniea coleothrypta, the membrane is clearly intratabular but mirrors plate boundaries. In others, such as Charlesdowniea edwardsii, the processes and the interconnected membranes are largely restricted to the ambital region. Other genera besides Charlesdowniea possessing an equiepeliform archeopyle are Apectodinium, Axiodinium, Epelidinium, Sophismatia and Vallodinium. Apectodinium and Axiodinium have processes that are distally free; Epelidinium has a pericyst surface that is smooth or ornamented with features of low relief; Sophismatia is characterised by processes joined by trabecula; and Vallodinium has sutural to penitabular ornamentation on the pericyst. Piladinium and Talladinium also have a membranous ectophragm, but have latiepeliform and soleiform archeopyles respectively.