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Dissimulidinium lobispinosum
Dissimulidinium lobispinosum May et al., 1987, p.201-203, figs.2A-D,3A-N,4A-I.
Holotype: May et al., 1987, figs.4A-C; Fensome et al., 1996, figs.1-3 - p.2201.
Locus typicus: Canning Basin, W Australia
Age: Berriasian.
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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.
Dissimulidinium lobispinosum May et al., 1987. This is trilobate with the dorsal lobe sometimes longer. Periphragm is punctoreticulate. Processes are solid, 5-10 µm long with distally expanded and recurved tips and concentrated on the lobes. Operculum usually free but sometimes adherent. Short accessory archeopyle sutures developed. Size: cyst length 50-60 µm, length increased by 5-8 µm when operculum present, hypocyst width 50-60 µm, epicyst width 22-36 µm, equatorial constriction 22-36 µm wide.
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Original description: May et al., 1987, p. 201-203
Cysts trilobate in lateral view with one epicystal and two hypocystal lobes. Hypocystal lobes broadly rounded in outline, more or less equal in size, or with the dorsal lobe somewhat longer (Fig.4G,I). Epicystal lobe commonly expanded apically, rounded to truncate margin may be inclined posteroventrally. Cysts elongate ellipsoidal in dorsoventral view. Endophragm and periphragm appressed and total 1-1.5 Ám in thickness (Fig.2C), the former being smooth and the latter punctoreticulate with uniformly distributed punctae, less than 1 Ám in diameter. Solid slender processes 5-10 Ám long and less than 1 Ám in diameter (Fig. 2C,D) with distally expanded and recurved tips concentrated on the lobes. Archeopyle apical type [tA], with a zigzag principal suture and posteroventrally sloping lateral margins. Operculum free and typically missing, adherent opercula sometimes present (Fig.4A-C). No isolated opercula observed. Paratabulation evident only from the archeopyIe a margin and short accessory parasutures; 6 precingular plates indicated. Paracingulum not indicated, snterior end of the parasulcus inferred from the ofiset position of the sulcal notch. Measurements for 15 of 40 studied specimens: cyst length (dehisced) 50(58.5)60 Ám, length increased by 5-8 Ám when operculum present, hypocyst width 50(56)60 Ám, epicyst width 22(28)36 Ám, equatorial constriction 22(28)36 Ám wide.
Variability. Cyst size and shape in lateral view vary considerably as a result of the development of longer hypocystal lobes, a larger dorsal hypocystal lobe and a flared epicystal lobe (Fig.3). Cysts are generally observed in lateral view, though some specimens are seen in apical/antapical view, allowing the lateral compression of the cyst and archeopyle to be noted (Fig.2B), and in oblique view, showing the ventral surface with the sulcal notch located at the anterior margin (Fig.4D-F). Process tips are expanded and are slightly to strongly recurved (Fig.2D). Opercula are generally free and only 5% to 10% of the species population display opercula in place (Fig.4A-C).
Affinities:
May et al., 1987, p. 203: Dissimulidinium lobispinosum is superficially similar to a number of species having quadrilobate or hourglass outlines, but differs from all these species by being compressed laterally and having a well-defined apical archeopyle with the principal suture often showing accessory sutures as well as a clear sulcal notch. Stenopyxinium grassei Deflandre 1968 differs also by having a combination [tAtP] archeopyle and an annular equatorial band; Quadrina pallida Bujak 1980 differs by having a smooth thin wall and ribbon-like processes with acuminate or rounded tips rather than expanded and recurved process tips; and Horologinella spinosigibberosa Brideaux & Fischer 1976 differs in having a uniformly distributed low relief ornament. In the Western Australian sedimentary basins there are at least two other superficially similar but as yet undescribed species which overlap in stratigraphic range with D. Iobispinosum. One has been described by Wiseman (1980) under the name Stenopyxinium s p. A. Both differ from D. Iobispinosum by being compressed dorsoventrally and having a more distinct quadrilobate outline, with a finer, denser and more evenly distributed ornament of hairs or spines with acuminate tips.
Holotype: May et al., 1987, figs.4A-C; Fensome et al., 1996, figs.1-3 - p.2201.
Locus typicus: Canning Basin, W Australia
Age: Berriasian.
--------------------------------------------------
G.L. Williams short notes on species, Mesozoic-Cenozoic dinocyst course, Urbino, Italy, May 17-22, 1999 - LPP VIEWER CD-ROM 99.5.
Dissimulidinium lobispinosum May et al., 1987. This is trilobate with the dorsal lobe sometimes longer. Periphragm is punctoreticulate. Processes are solid, 5-10 µm long with distally expanded and recurved tips and concentrated on the lobes. Operculum usually free but sometimes adherent. Short accessory archeopyle sutures developed. Size: cyst length 50-60 µm, length increased by 5-8 µm when operculum present, hypocyst width 50-60 µm, epicyst width 22-36 µm, equatorial constriction 22-36 µm wide.
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Original description: May et al., 1987, p. 201-203
Cysts trilobate in lateral view with one epicystal and two hypocystal lobes. Hypocystal lobes broadly rounded in outline, more or less equal in size, or with the dorsal lobe somewhat longer (Fig.4G,I). Epicystal lobe commonly expanded apically, rounded to truncate margin may be inclined posteroventrally. Cysts elongate ellipsoidal in dorsoventral view. Endophragm and periphragm appressed and total 1-1.5 Ám in thickness (Fig.2C), the former being smooth and the latter punctoreticulate with uniformly distributed punctae, less than 1 Ám in diameter. Solid slender processes 5-10 Ám long and less than 1 Ám in diameter (Fig. 2C,D) with distally expanded and recurved tips concentrated on the lobes. Archeopyle apical type [tA], with a zigzag principal suture and posteroventrally sloping lateral margins. Operculum free and typically missing, adherent opercula sometimes present (Fig.4A-C). No isolated opercula observed. Paratabulation evident only from the archeopyIe a margin and short accessory parasutures; 6 precingular plates indicated. Paracingulum not indicated, snterior end of the parasulcus inferred from the ofiset position of the sulcal notch. Measurements for 15 of 40 studied specimens: cyst length (dehisced) 50(58.5)60 Ám, length increased by 5-8 Ám when operculum present, hypocyst width 50(56)60 Ám, epicyst width 22(28)36 Ám, equatorial constriction 22(28)36 Ám wide.
Variability. Cyst size and shape in lateral view vary considerably as a result of the development of longer hypocystal lobes, a larger dorsal hypocystal lobe and a flared epicystal lobe (Fig.3). Cysts are generally observed in lateral view, though some specimens are seen in apical/antapical view, allowing the lateral compression of the cyst and archeopyle to be noted (Fig.2B), and in oblique view, showing the ventral surface with the sulcal notch located at the anterior margin (Fig.4D-F). Process tips are expanded and are slightly to strongly recurved (Fig.2D). Opercula are generally free and only 5% to 10% of the species population display opercula in place (Fig.4A-C).
Affinities:
May et al., 1987, p. 203: Dissimulidinium lobispinosum is superficially similar to a number of species having quadrilobate or hourglass outlines, but differs from all these species by being compressed laterally and having a well-defined apical archeopyle with the principal suture often showing accessory sutures as well as a clear sulcal notch. Stenopyxinium grassei Deflandre 1968 differs also by having a combination [tAtP] archeopyle and an annular equatorial band; Quadrina pallida Bujak 1980 differs by having a smooth thin wall and ribbon-like processes with acuminate or rounded tips rather than expanded and recurved process tips; and Horologinella spinosigibberosa Brideaux & Fischer 1976 differs in having a uniformly distributed low relief ornament. In the Western Australian sedimentary basins there are at least two other superficially similar but as yet undescribed species which overlap in stratigraphic range with D. Iobispinosum. One has been described by Wiseman (1980) under the name Stenopyxinium s p. A. Both differ from D. Iobispinosum by being compressed dorsoventrally and having a more distinct quadrilobate outline, with a finer, denser and more evenly distributed ornament of hairs or spines with acuminate tips.