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Microdinium spinosum
Microdinium spinosum Brideaux and McIntyre, 1975
Taxonomic senior synonym: Microdinium (as Phanerodinium) opacum, according to Below (1987b, p.38).
Holotype: Brideaux and McIntyre, 1975, pl.6, figs.3-4
Age: Middle Albian
Original description (Brideaux & McIntre, 1975):
Microdinium spinosum sp. nov. Plate 6, figures 3-5
Holotype. GSC No. 34148; Slide 6884-2, 13.4 x 133.2; Horton River Formation, Section CR15A-68, 30 to 37 feet (9.1 to 11. m), GSC loc. C- 8534; Middle Albian. Length, 28μ (archeopyle present); width, 28μ.
Diagnosis . Proximate dinoflagellate cyst; thin walled; tabulation, ?4', 6", 6c, 5'",_ lp, 1’’’’, l-4s; low sutural crests bearing spinulose processes, or sutural rows of ·coni or pila outline the reflected tabulation. Cingulum slightly sinistral; sulcus S-shaped. A nearly circular darkened spot always present at latitude of reflected plate 3"' .
Description. The preferred orientation of the cyst is always dorso-ventral. The outline is roughly hexagonal, but not strongly angular; the antapex is gently rounded. The epitract length is always distinctly less than the hypotract length. The overall length to width ratio is very close to 1.0 with the greatest width occurring just below the latitude of the cingulum. The wall is about 1.0 µm thick in optical section. Intartabular crests bearing small spinulose processes, about 0.5 to 1.0μ high, or rows of coni or pila, 0.5 to 1.5μ high, outline the reflected tabulation. The intratabular wall surface is generally scabrate, although well-preserved specimens possess a fine microgranulate design of great complexity on some reflected plates. A central darkened region is present on all specimens encountered, lying in the latitude of reflected plate 3"' and extending into the cingular region. The wall does not appear to be thicker in this darkened area. All specimens are dark brown to brownish yellow in colour. The archeopyle is apical and possibly composed of four apical reflected plates. It is difficult, however, to confirm this from the Horton Rvier specimens. The operculum is absent or, when present, is detached but lies in the archeopyle. It is never well preserved and appears to have undergone chemical degradation. The tabulation pattern has been determined as ?4', 6", 6c, 5"', lp, 1’’’’ , l-4s. Four reflected sulcul plates, the anterior, left, right, and posterior, are distinguishable. Precingular reflected plates 3" and 4" are quite small and nearly rectangular. The postcingular reflected plates 1’’’ to 5"' and reflected plates lp and l"" are quite large compared to the precingular series. Cingular reflected plates are defined by very low, fine ridges and are somewhat rectangular . The anterior sulcal reflected plate may or may not be delimited from the rest of the sulcus, and is harp-shaped, the narrower end towards the antapex. The cingulum is slightly sinistral. The sulcus is S-shaped, widest at the boundary with reflected plate l"", narrowing at the base of the anterior sulcal reflected plate and widening slightly before reaching the edge of the archeopyle.
Dimensions. (18 measured specimens) - Length, 25 - 32μ; width, 25 -34μ.
Comparison. Microdinium spinosum sp. nov . differs from M. ornatum Cookson and Eisenack (1960a, p. 5) in its reflected tabulation pattern and possession of a circular darkened area, from M. sp. cf . M. ornatum Cookson and Eisenack (in Sarjeant, 1966a, p . 149) in its reflected tabulation and possession of a darkened patch, and from M. setosiun Sarjeant (1966a, p. 151) in details of reflected tabulation and the possession of smaller sutural crests or spine rows and a central darkened region.
Microdinium opacum Brideaux (197lb, p. 76) most closely resembles M. spinosum sp. nov. Both
species have a central darkened patch, similar reflected sulcal tabulation, archeopyle and operculum structure. But M. spinosum possesses reflected tabulation delimited by rows of coni, pila, or spinulose crests, whereas M. opacum shows smooth low ridges or crests. Furthermore, M. spinosum possesses only five reflected postcingular plates, in contrast to six for M. opacum, and differs in the shapes of the six reflected precingular plates. Glyphanodiniun facetum Drugg (1964, p. 238) possesses a faint central darkened area but differs from M. spinosum in several respects, notably in its markedly pentagonal outline and possession of six postcingular reflected plates .
Occurrence. Horton River Formation (Middle Albian).
Taxonomic senior synonym: Microdinium (as Phanerodinium) opacum, according to Below (1987b, p.38).
Holotype: Brideaux and McIntyre, 1975, pl.6, figs.3-4
Age: Middle Albian
Original description (Brideaux & McIntre, 1975):
Microdinium spinosum sp. nov. Plate 6, figures 3-5
Holotype. GSC No. 34148; Slide 6884-2, 13.4 x 133.2; Horton River Formation, Section CR15A-68, 30 to 37 feet (9.1 to 11. m), GSC loc. C- 8534; Middle Albian. Length, 28μ (archeopyle present); width, 28μ.
Diagnosis . Proximate dinoflagellate cyst; thin walled; tabulation, ?4', 6", 6c, 5'",_ lp, 1’’’’, l-4s; low sutural crests bearing spinulose processes, or sutural rows of ·coni or pila outline the reflected tabulation. Cingulum slightly sinistral; sulcus S-shaped. A nearly circular darkened spot always present at latitude of reflected plate 3"' .
Description. The preferred orientation of the cyst is always dorso-ventral. The outline is roughly hexagonal, but not strongly angular; the antapex is gently rounded. The epitract length is always distinctly less than the hypotract length. The overall length to width ratio is very close to 1.0 with the greatest width occurring just below the latitude of the cingulum. The wall is about 1.0 µm thick in optical section. Intartabular crests bearing small spinulose processes, about 0.5 to 1.0μ high, or rows of coni or pila, 0.5 to 1.5μ high, outline the reflected tabulation. The intratabular wall surface is generally scabrate, although well-preserved specimens possess a fine microgranulate design of great complexity on some reflected plates. A central darkened region is present on all specimens encountered, lying in the latitude of reflected plate 3"' and extending into the cingular region. The wall does not appear to be thicker in this darkened area. All specimens are dark brown to brownish yellow in colour. The archeopyle is apical and possibly composed of four apical reflected plates. It is difficult, however, to confirm this from the Horton Rvier specimens. The operculum is absent or, when present, is detached but lies in the archeopyle. It is never well preserved and appears to have undergone chemical degradation. The tabulation pattern has been determined as ?4', 6", 6c, 5"', lp, 1’’’’ , l-4s. Four reflected sulcul plates, the anterior, left, right, and posterior, are distinguishable. Precingular reflected plates 3" and 4" are quite small and nearly rectangular. The postcingular reflected plates 1’’’ to 5"' and reflected plates lp and l"" are quite large compared to the precingular series. Cingular reflected plates are defined by very low, fine ridges and are somewhat rectangular . The anterior sulcal reflected plate may or may not be delimited from the rest of the sulcus, and is harp-shaped, the narrower end towards the antapex. The cingulum is slightly sinistral. The sulcus is S-shaped, widest at the boundary with reflected plate l"", narrowing at the base of the anterior sulcal reflected plate and widening slightly before reaching the edge of the archeopyle.
Dimensions. (18 measured specimens) - Length, 25 - 32μ; width, 25 -34μ.
Comparison. Microdinium spinosum sp. nov . differs from M. ornatum Cookson and Eisenack (1960a, p. 5) in its reflected tabulation pattern and possession of a circular darkened area, from M. sp. cf . M. ornatum Cookson and Eisenack (in Sarjeant, 1966a, p . 149) in its reflected tabulation and possession of a darkened patch, and from M. setosiun Sarjeant (1966a, p. 151) in details of reflected tabulation and the possession of smaller sutural crests or spine rows and a central darkened region.
Microdinium opacum Brideaux (197lb, p. 76) most closely resembles M. spinosum sp. nov. Both
species have a central darkened patch, similar reflected sulcal tabulation, archeopyle and operculum structure. But M. spinosum possesses reflected tabulation delimited by rows of coni, pila, or spinulose crests, whereas M. opacum shows smooth low ridges or crests. Furthermore, M. spinosum possesses only five reflected postcingular plates, in contrast to six for M. opacum, and differs in the shapes of the six reflected precingular plates. Glyphanodiniun facetum Drugg (1964, p. 238) possesses a faint central darkened area but differs from M. spinosum in several respects, notably in its markedly pentagonal outline and possession of six postcingular reflected plates .
Occurrence. Horton River Formation (Middle Albian).