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Microdinium opacum
Microdinium opacum Brideaux, 1971
Originally (and now) Microdinium, subsequently Phanerodinium.
Questionable tax. jr. synonym of Microdinium (as Phanerodinium) distinctum Davey, 1969, according to Below, 1987.
Tax. sr. synonym of Microdinium spinosum Brideaux and McIntyre, 1975, according to Below, 1987.
Below, 1987, transferred this species to Phanerodinium Deflandre, 1937. Lentin and Williams, 1989, retained it in Microdinium.
Holotype: Brideaux, 1971, pl.21, figs.21-22, text-fig.7d-e
Locus typicus: Alberta, Canada
Stratum typicum: Middle-Late Albian
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G.L. Williams short notes on species, Mesozoic-Cenozoic dinocyst course, Urbino, Italy, May 17-22, 1999 - LPP VIEWER CD-ROM 99.5.
Microdinium opacum Brideaux, 1971, has a somewhat pentagonal shape, with the epicyst smaller than the hypocyst. Apical archeopyle formed by the loss of one or more apical plates. Plates outlined by low simple ridges. The cyst bears a circular darkened ?thickened region at and just below the level of the cingulum, the diameter of which is about one-half that of the cyst. Size: length 19-36 µm, width 22-33 µm, width of darkened spot 7-17 µm.
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Original description (Holotype): Brideaux, 1971, p.76-77
Size Holotype: Length, 28 Ám, width, 25 Ám; diameter of darkened region, 13 Ám. Tabulation: 1'?, 6", 6c, 6''', 1p, 1''''. Outline somewhat pentagonal with corners rounded. Low, narrow ridges about 1--1¢ Ám high outline reflected tabulation. Cingulum nearly circular, slightly sinistral, the plates nearly rectangular with plate 3c somewhat larger; sulcus extends from near the antapex onto the epitract, widest at the antapex and narrowing on the epitract, terminated by the apical plate series. Precingular plate series nearly equal in size with plate 3" somewhat wider; in the post-cingular series, plate 1''' trianguloid, plate 6''' larger than the others. Antapical plate displaced to the left of the vertical axis; plate I p extending only slightly onto the dorsal surface. The darkened region at the mid-cyst line is nearly circular. Operculum present. irregularly shaped, outline not clearly defined and tabulation not determinable; detached from the main cyst body but clearly associated with it. Cyst wall dark brown colour.
Description: Brideaux, 1971, p.77
Dinoflagellate cyst, pentagonal shape, corners rounded; epitract smaller than hypotract. Apical archeopyle formed by the loss of one or more apical plates; operculum diffuse in outline, appearing somewhat degraded in all cases observed; tabulation not observed, but interpreted as 1'. Reflected tabulation of the remaining cyst determined as 1'?, 6", 6 c, 6''', 1p and 1'''', the plating outlined by low, simple, straight ridges. The cyst bears a circular, darkened, ?thickened region at and just below the level of the cingulum, the diameter of which is approximately one-half the total cyst diameter. The slightly sinistral cingulum is provided with six plates, the outlines not always completely defined and not co-inciding in emplacement with more than one or two plates of the pre-cingular or post-cingular series. Sulcus somewhat flask-shaped with a rounded to angular outline, extending onto the epitract adjacent to the apical plate series and terminated antapically by plate 1''''. Plates 6", 1" and 6''', 1''' often encroach, making the sulcus narrow in this region. Plate 1''' smaller than other post-cingular plates; plate 6''' somewhat trapezoidal in outline. The antapical plate is placed slightly asymmetrically with respect to the longitudinal axis. All specimens encountered have a light to dark brown colour.
Dimensions: Length on 40 measured specimens, 19-36 Ám; width on 12 measured specimens, 22-33 Ám; width of darkened spot, 7-17 Ám.
Affinities:
Brideaux, 1971, p.77: Glyphanodinium facetum Drugg, 1967 is similar in many respects to Microdinium opacum but differs in the tabulation pattern.
Originally (and now) Microdinium, subsequently Phanerodinium.
Questionable tax. jr. synonym of Microdinium (as Phanerodinium) distinctum Davey, 1969, according to Below, 1987.
Tax. sr. synonym of Microdinium spinosum Brideaux and McIntyre, 1975, according to Below, 1987.
Below, 1987, transferred this species to Phanerodinium Deflandre, 1937. Lentin and Williams, 1989, retained it in Microdinium.
Holotype: Brideaux, 1971, pl.21, figs.21-22, text-fig.7d-e
Locus typicus: Alberta, Canada
Stratum typicum: Middle-Late Albian
--------------------------------------------------
G.L. Williams short notes on species, Mesozoic-Cenozoic dinocyst course, Urbino, Italy, May 17-22, 1999 - LPP VIEWER CD-ROM 99.5.
Microdinium opacum Brideaux, 1971, has a somewhat pentagonal shape, with the epicyst smaller than the hypocyst. Apical archeopyle formed by the loss of one or more apical plates. Plates outlined by low simple ridges. The cyst bears a circular darkened ?thickened region at and just below the level of the cingulum, the diameter of which is about one-half that of the cyst. Size: length 19-36 µm, width 22-33 µm, width of darkened spot 7-17 µm.
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Original description (Holotype): Brideaux, 1971, p.76-77
Size Holotype: Length, 28 Ám, width, 25 Ám; diameter of darkened region, 13 Ám. Tabulation: 1'?, 6", 6c, 6''', 1p, 1''''. Outline somewhat pentagonal with corners rounded. Low, narrow ridges about 1--1¢ Ám high outline reflected tabulation. Cingulum nearly circular, slightly sinistral, the plates nearly rectangular with plate 3c somewhat larger; sulcus extends from near the antapex onto the epitract, widest at the antapex and narrowing on the epitract, terminated by the apical plate series. Precingular plate series nearly equal in size with plate 3" somewhat wider; in the post-cingular series, plate 1''' trianguloid, plate 6''' larger than the others. Antapical plate displaced to the left of the vertical axis; plate I p extending only slightly onto the dorsal surface. The darkened region at the mid-cyst line is nearly circular. Operculum present. irregularly shaped, outline not clearly defined and tabulation not determinable; detached from the main cyst body but clearly associated with it. Cyst wall dark brown colour.
Description: Brideaux, 1971, p.77
Dinoflagellate cyst, pentagonal shape, corners rounded; epitract smaller than hypotract. Apical archeopyle formed by the loss of one or more apical plates; operculum diffuse in outline, appearing somewhat degraded in all cases observed; tabulation not observed, but interpreted as 1'. Reflected tabulation of the remaining cyst determined as 1'?, 6", 6 c, 6''', 1p and 1'''', the plating outlined by low, simple, straight ridges. The cyst bears a circular, darkened, ?thickened region at and just below the level of the cingulum, the diameter of which is approximately one-half the total cyst diameter. The slightly sinistral cingulum is provided with six plates, the outlines not always completely defined and not co-inciding in emplacement with more than one or two plates of the pre-cingular or post-cingular series. Sulcus somewhat flask-shaped with a rounded to angular outline, extending onto the epitract adjacent to the apical plate series and terminated antapically by plate 1''''. Plates 6", 1" and 6''', 1''' often encroach, making the sulcus narrow in this region. Plate 1''' smaller than other post-cingular plates; plate 6''' somewhat trapezoidal in outline. The antapical plate is placed slightly asymmetrically with respect to the longitudinal axis. All specimens encountered have a light to dark brown colour.
Dimensions: Length on 40 measured specimens, 19-36 Ám; width on 12 measured specimens, 22-33 Ám; width of darkened spot, 7-17 Ám.
Affinities:
Brideaux, 1971, p.77: Glyphanodinium facetum Drugg, 1967 is similar in many respects to Microdinium opacum but differs in the tabulation pattern.