Back
Ellipsoidictyum imperfectum
Ellipsoidictyum imperfectum (Brideaux and McIntyre, 1975) Lentin and Williams, 1977
Originally Dictyopyxidia, subsequently (and now) Ellipsoidictyum.
Holotype: Brideaux and McIntyre, 1975, pl.7, figs.1-3
Locus typicus: Horton River, District of Mackenzie, Canada
Stratum typicum: Early-Middle Albian
--------------------------------------------------
G.L. Williams short notes on species, Mesozoic-Cenozoic dinocyst course, Urbino, Italy, May 17-22, 1999 - LPP VIEWER CD-ROM 99.5.
Ellipsoidictyum imperfectum (Brideaux and McIntyre, 1975) Lentin and Williams, 1977b, is subcircular to oval proximate cyst. Wall two-layered, endophragm simple; periphragm forming a low, perfect to imperfect reticulate network, the lumina highly variable in shape and size; a sinistral cingulum, and sulcal region, outlined respectively by a transverse, elongate pair of low ridges and an absence or reduction of the reticulum. Apical archeopyle with free operculum. Size: length 45-68 µm, width 40-62 µm.
--------------------------------------------------
Original diagnosis: Brideaux and McIntyre, 1975, p. 25: Dictyopyxidia imperfecta
Subcircular to oval proximate dinoflagellate cyst. Wall two-layered; endophragm simple; periphragm forming a low, perfect to imperfect, reticulate network, the lumina highly variable in size and shape; a sinistral cingulum, and sulcal region, outlined respectively by a transverse, elongate pair of low ridges and an absence or reduction of the reticulum. Archeopyle apical, operculum simple and free, polygonal; tabulation not determinable.
Original description: Brideaux and McIntyre, 1975, p. 25-26: Dictyopyxidia imperfecta
The proximate cyst generally is oriented dorsoventrally on the slide. The overall outline of the cyst is subcircular to oval, although some specimens may be slightly angular. The apex and antapex are gently rounded and possess no prominences. The length of the epitract is equal to or slightly less than the hypotract. The greatest width of the cyst occurs at or near the latitude of the cingulum.
The wall is two layered. The endophragm is about 1.0 Ám thick in optical section. The periphragm forms a very low, perfect to imperfect reticulum. The muri are 0.5 to 1.0 Ám high and from 1.0 to 1.5 Ám wide and enclose ovoid to polygonal lumina of variable maximum diameter. On rare specimens, the muri become partly detached and may be up to 4 Ám high. The structure of the muri appears to be somewhat fibrous.
A curious condition occurs in many specimens from Section CR14A-68 (Horton River Formation). The reticulate layer is severely reduced over the whole of the cyst so that only low, flattened, papillate-like processes, alone, or in combination with patchy remnants of reticulum remain.
The cingulum is distinct on most specimens, sinistral, displaced from one to two cingulum widths and 5 to 8 Ám wide. It is formed by a pair of slightly more prominent, transversely oriented low sutures, interconnected with the main reticulum. This pair of ridges is interrupted on the ventral surface by the sulcal region, defined by a marked reduction or complete absence of a reticulum. Rare, low ridges connect the main cingular ridges, but no angular reflected tabulation is evident. The sulcus is terminated at the antapex by the reticulum and on the epitract by a prominent sulcul notch. The position of the notch and the course of the sulcus indicate that the sulcus is not offset.
The archeopyle is apical and formed by the loss of the reflected plates of the apical series. The outline is variably zig-zag and includes the distinct sulcal notch. The operculum is simple, free, and is rarely found in place or partially attached. It is visible in a few instances and is five sided and angular in outline suggesting four reflected apical plates, and bears a similar low reticulum to that of the main cyst body. Individual reflected plates are not determinable.
The tabulation of the species, with the exception of the apical series, is not determinable; the low reticulum does not appear sufficiently differentiated to permit the recognition of a reflected tabulation pattern.
Dimensions: Length, 45-68 Ám; width, 40-62 Ám.
Affinities:
Brideaux and McIntyre, 1975, p.26: Dictyopyxidia imperfecta
Dictyopyxidia imperfecta differs from D. circulata Clarke and Verdier (1967, p. 67) in the presence of a relatively pronounced cingulum and distinct sulcal region, in having an imperfect to severely reduced reticulum, and in being of generally larger size. Dictyopyxidia imperfecta differs from the type species D. aerolata (Cookson and Eisenack) Eisenack in being more or less equidimensional rather than distinctly elongate, in having a low, imperfect, rather than regular, distinct reticulum, in having a defined rather than indistinct cingulum, and in being of generally smaller size.
Originally Dictyopyxidia, subsequently (and now) Ellipsoidictyum.
Holotype: Brideaux and McIntyre, 1975, pl.7, figs.1-3
Locus typicus: Horton River, District of Mackenzie, Canada
Stratum typicum: Early-Middle Albian
--------------------------------------------------
G.L. Williams short notes on species, Mesozoic-Cenozoic dinocyst course, Urbino, Italy, May 17-22, 1999 - LPP VIEWER CD-ROM 99.5.
Ellipsoidictyum imperfectum (Brideaux and McIntyre, 1975) Lentin and Williams, 1977b, is subcircular to oval proximate cyst. Wall two-layered, endophragm simple; periphragm forming a low, perfect to imperfect reticulate network, the lumina highly variable in shape and size; a sinistral cingulum, and sulcal region, outlined respectively by a transverse, elongate pair of low ridges and an absence or reduction of the reticulum. Apical archeopyle with free operculum. Size: length 45-68 µm, width 40-62 µm.
--------------------------------------------------
Original diagnosis: Brideaux and McIntyre, 1975, p. 25: Dictyopyxidia imperfecta
Subcircular to oval proximate dinoflagellate cyst. Wall two-layered; endophragm simple; periphragm forming a low, perfect to imperfect, reticulate network, the lumina highly variable in size and shape; a sinistral cingulum, and sulcal region, outlined respectively by a transverse, elongate pair of low ridges and an absence or reduction of the reticulum. Archeopyle apical, operculum simple and free, polygonal; tabulation not determinable.
Original description: Brideaux and McIntyre, 1975, p. 25-26: Dictyopyxidia imperfecta
The proximate cyst generally is oriented dorsoventrally on the slide. The overall outline of the cyst is subcircular to oval, although some specimens may be slightly angular. The apex and antapex are gently rounded and possess no prominences. The length of the epitract is equal to or slightly less than the hypotract. The greatest width of the cyst occurs at or near the latitude of the cingulum.
The wall is two layered. The endophragm is about 1.0 Ám thick in optical section. The periphragm forms a very low, perfect to imperfect reticulum. The muri are 0.5 to 1.0 Ám high and from 1.0 to 1.5 Ám wide and enclose ovoid to polygonal lumina of variable maximum diameter. On rare specimens, the muri become partly detached and may be up to 4 Ám high. The structure of the muri appears to be somewhat fibrous.
A curious condition occurs in many specimens from Section CR14A-68 (Horton River Formation). The reticulate layer is severely reduced over the whole of the cyst so that only low, flattened, papillate-like processes, alone, or in combination with patchy remnants of reticulum remain.
The cingulum is distinct on most specimens, sinistral, displaced from one to two cingulum widths and 5 to 8 Ám wide. It is formed by a pair of slightly more prominent, transversely oriented low sutures, interconnected with the main reticulum. This pair of ridges is interrupted on the ventral surface by the sulcal region, defined by a marked reduction or complete absence of a reticulum. Rare, low ridges connect the main cingular ridges, but no angular reflected tabulation is evident. The sulcus is terminated at the antapex by the reticulum and on the epitract by a prominent sulcul notch. The position of the notch and the course of the sulcus indicate that the sulcus is not offset.
The archeopyle is apical and formed by the loss of the reflected plates of the apical series. The outline is variably zig-zag and includes the distinct sulcal notch. The operculum is simple, free, and is rarely found in place or partially attached. It is visible in a few instances and is five sided and angular in outline suggesting four reflected apical plates, and bears a similar low reticulum to that of the main cyst body. Individual reflected plates are not determinable.
The tabulation of the species, with the exception of the apical series, is not determinable; the low reticulum does not appear sufficiently differentiated to permit the recognition of a reflected tabulation pattern.
Dimensions: Length, 45-68 Ám; width, 40-62 Ám.
Affinities:
Brideaux and McIntyre, 1975, p.26: Dictyopyxidia imperfecta
Dictyopyxidia imperfecta differs from D. circulata Clarke and Verdier (1967, p. 67) in the presence of a relatively pronounced cingulum and distinct sulcal region, in having an imperfect to severely reduced reticulum, and in being of generally larger size. Dictyopyxidia imperfecta differs from the type species D. aerolata (Cookson and Eisenack) Eisenack in being more or less equidimensional rather than distinctly elongate, in having a low, imperfect, rather than regular, distinct reticulum, in having a defined rather than indistinct cingulum, and in being of generally smaller size.