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Limbodinium absidatum
Limbodinium absidatum (Drugg, 1978, p.66–67, pl.4, figs.7–9) Riding, 1987b, p.60. Emendation: Riding, 1987b, p.60,62, as Limbodinium absidatum.
Originally Dinopterygium, subsequently Dinopterygium?, thirdly (and now) Limbodinium.
Holotype: Drugg, 1978, pl. 4, fig. 7; Riding, 1987, pl.1, fig.7
Paratypes: Drugg, 1978
Locus typicus: Warboys Brick pit, Huntingdonshire, England
Stratum typicum: Late Callovian-Middle Oxfordian
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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.
Limbodinium absidatum (Drugg, 1978) Riding, 1987b, emend. Riding, 1987b. According to Riding (1987b), this species is suturocavate at the antapical parasutures, both paracingular flanges and occasionally at the pre- and postcingular parasutures. Endophragm and periphragm smooth to faintly ornamented. Epicyst nontabulate except for low, smooth, precingular parasutural ridges. Hypocyst partly to fully tabulate. The postcingular parasutures may be denticulate. At and immediately adjacent to the antapical paraplate, the parasutural ridges become distinct crests which may bear small denticles. The posterior paracingular flange is strongly denticulate and often slightly wider than the distally smooth anterior counterpart, which is also cavate. The claustra in the anterior layer of the posterior paracingular flange are subtriangular in outline and extend to the outer rim of the flange, where the outwardly convex sides converge to form a sharply pointed tip. The ventral organization is L-type, with the hypocyst being sexiform. The archeopyle is hemicystal, with the archeopyle suture running along the cingulum and with the operculum attached ventrally. Size: cyst diameter 73-112 µm.
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Original description: Drugg, 1978, p.66-67
Diagnosis: In polar view the cyst is more or less circular in outline with a parasulcal depression. The paracingular flages are absent in the region of the parasulcal re-entrant. The exact shape of the epicyst is unknown but is probably a very low cone. The hypocyst is a modified cone in shape and bears antapical extensions formed from the periphragm. The ventral side of the hypocyst is apparently quite flat in view of the fact that the cysts almost invariably assume a preferred orientation the slide. Theis planar surface is sloped towards the antapex. The mode of archeopyle formation is epicystal. The paracingulum is prominent and is delineated ledges from 8 to 113 Ám in width. The outline of the epicystal paracingular flange is somewhat angular and outer edges are slightly ragged. The hypocystal flange is more rounded in outline and the edges are deticulate in varying degrees. The periphragm of the hypocystal paracingular flange exhibits five arch-like openings which are convex outward. Often there are subsidiary elliptical openings of varying size and distribution. The endophragm is intact underneath. Both endophragm and periphragm are thin and shagreen to finely granulate. Paratabuation is present but is obscure. Low denticulate parasutural crests extend part way down the hypocyst, then disappear for aways, and then re-appear near the antapex. Those on the epicyst are onlyu visisble in the vicinity of the paracingular ledges. The paratabulation is apperently ?4', 6'', xc, 6''', ?1p, 1''''. The cyst diameter, including the paracingular flanges, ranges from 73 to 112 Ám with most being about 85 Ám. Size range based on measurements of 33 species.
Emended diagnosis: Riding, 1987, p. 60, 62
A species of Limbodinium which is suturocavate at the antapical parasutures, both paracingular flanges and occasionally at the pre- and postcingular parasutures. Endophragm and periphragm smooth to faintly ornamented. Epicyst nonparatabulate except for low, smooth precingular parasutural ridges, discontinuous toward the apex. These ridges extend for one-third to one-half the radius of the epicyst and form tips at the margin of the anterior paracingular flange. Hypocyst partially to fully paratabulate, the postcingular paraplates are delineated by discontinuous to continuous parasutural ridges. The postcingular parasutures may be interrupted in the center of the hypocyst for up to one third of the hypocystal length and may be denticulate. These ridges form tips at the margins of the posterior paracingular flange. At, and immediately adjacent to the antapical paraplate, the parasutural ridges become distinct crests which may bear small, irregular denticles. The posterior paracingular flange is strongly denticulate and often slightly wider than the distally smooth anterior counterpart which is also cavate. Both paracingular flanges exhibit a relatively narrow acavate area at the distal flange edge. The calustra in the anterior layer of the posterior paracingular flange are subtriangular in outline and extend to the outer rim of the flange where the outwardly convex sides converge to form a sharply pointed tip. The anterior layer of the posterior paracingular flange may also exhibit small, irregular subcircular to elongate ovoidal perforations. Parasulcus relatively wide, in a shallow depression, not subdivided into paraplates. Paracingular flanges absent over the parasulcal area.
Dimensions (annotated): 43 specimens measured. Length: 71-88 µm. Overall width: 67-105 µm. Width of cyst excl. paracing.: 43-69 µm. Maximum posterior paracingular flange: 6-16 µm. Maximum width of anterior paracingular flange: 5-14 µm. Diameter of claustra: 6-14 µm.
Affinities:
Drugg, 1978, p. 66-67
Interpretation of the species is rendered difficult by the monotonous preferred orientation. The arch-like openings in the periphragm of the hypocystal paracingular flanges are highly distinctive and make identification easy even in fragmented examples. The allocation of this species to the genus Dinopterygium seems reasonable although the morphology aso suggests affinities with Ctenidodinium and Wanea. This species appears to be a good marker for the Callovian and basal Oxfordian.
Riding, 1987, p. 62
Limbodinium absidatum is distinguished from other forms of Limbodinium (Limbodinium sp., L. cf. L. absidatum), by the often discontinuous nature of the precingular parasutures and the wide, strongly denticulate posterior paracingular flange.
Originally Dinopterygium, subsequently Dinopterygium?, thirdly (and now) Limbodinium.
Holotype: Drugg, 1978, pl. 4, fig. 7; Riding, 1987, pl.1, fig.7
Paratypes: Drugg, 1978
Locus typicus: Warboys Brick pit, Huntingdonshire, England
Stratum typicum: Late Callovian-Middle Oxfordian
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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.
Limbodinium absidatum (Drugg, 1978) Riding, 1987b, emend. Riding, 1987b. According to Riding (1987b), this species is suturocavate at the antapical parasutures, both paracingular flanges and occasionally at the pre- and postcingular parasutures. Endophragm and periphragm smooth to faintly ornamented. Epicyst nontabulate except for low, smooth, precingular parasutural ridges. Hypocyst partly to fully tabulate. The postcingular parasutures may be denticulate. At and immediately adjacent to the antapical paraplate, the parasutural ridges become distinct crests which may bear small denticles. The posterior paracingular flange is strongly denticulate and often slightly wider than the distally smooth anterior counterpart, which is also cavate. The claustra in the anterior layer of the posterior paracingular flange are subtriangular in outline and extend to the outer rim of the flange, where the outwardly convex sides converge to form a sharply pointed tip. The ventral organization is L-type, with the hypocyst being sexiform. The archeopyle is hemicystal, with the archeopyle suture running along the cingulum and with the operculum attached ventrally. Size: cyst diameter 73-112 µm.
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Original description: Drugg, 1978, p.66-67
Diagnosis: In polar view the cyst is more or less circular in outline with a parasulcal depression. The paracingular flages are absent in the region of the parasulcal re-entrant. The exact shape of the epicyst is unknown but is probably a very low cone. The hypocyst is a modified cone in shape and bears antapical extensions formed from the periphragm. The ventral side of the hypocyst is apparently quite flat in view of the fact that the cysts almost invariably assume a preferred orientation the slide. Theis planar surface is sloped towards the antapex. The mode of archeopyle formation is epicystal. The paracingulum is prominent and is delineated ledges from 8 to 113 Ám in width. The outline of the epicystal paracingular flange is somewhat angular and outer edges are slightly ragged. The hypocystal flange is more rounded in outline and the edges are deticulate in varying degrees. The periphragm of the hypocystal paracingular flange exhibits five arch-like openings which are convex outward. Often there are subsidiary elliptical openings of varying size and distribution. The endophragm is intact underneath. Both endophragm and periphragm are thin and shagreen to finely granulate. Paratabuation is present but is obscure. Low denticulate parasutural crests extend part way down the hypocyst, then disappear for aways, and then re-appear near the antapex. Those on the epicyst are onlyu visisble in the vicinity of the paracingular ledges. The paratabulation is apperently ?4', 6'', xc, 6''', ?1p, 1''''. The cyst diameter, including the paracingular flanges, ranges from 73 to 112 Ám with most being about 85 Ám. Size range based on measurements of 33 species.
Emended diagnosis: Riding, 1987, p. 60, 62
A species of Limbodinium which is suturocavate at the antapical parasutures, both paracingular flanges and occasionally at the pre- and postcingular parasutures. Endophragm and periphragm smooth to faintly ornamented. Epicyst nonparatabulate except for low, smooth precingular parasutural ridges, discontinuous toward the apex. These ridges extend for one-third to one-half the radius of the epicyst and form tips at the margin of the anterior paracingular flange. Hypocyst partially to fully paratabulate, the postcingular paraplates are delineated by discontinuous to continuous parasutural ridges. The postcingular parasutures may be interrupted in the center of the hypocyst for up to one third of the hypocystal length and may be denticulate. These ridges form tips at the margins of the posterior paracingular flange. At, and immediately adjacent to the antapical paraplate, the parasutural ridges become distinct crests which may bear small, irregular denticles. The posterior paracingular flange is strongly denticulate and often slightly wider than the distally smooth anterior counterpart which is also cavate. Both paracingular flanges exhibit a relatively narrow acavate area at the distal flange edge. The calustra in the anterior layer of the posterior paracingular flange are subtriangular in outline and extend to the outer rim of the flange where the outwardly convex sides converge to form a sharply pointed tip. The anterior layer of the posterior paracingular flange may also exhibit small, irregular subcircular to elongate ovoidal perforations. Parasulcus relatively wide, in a shallow depression, not subdivided into paraplates. Paracingular flanges absent over the parasulcal area.
Dimensions (annotated): 43 specimens measured. Length: 71-88 µm. Overall width: 67-105 µm. Width of cyst excl. paracing.: 43-69 µm. Maximum posterior paracingular flange: 6-16 µm. Maximum width of anterior paracingular flange: 5-14 µm. Diameter of claustra: 6-14 µm.
Affinities:
Drugg, 1978, p. 66-67
Interpretation of the species is rendered difficult by the monotonous preferred orientation. The arch-like openings in the periphragm of the hypocystal paracingular flanges are highly distinctive and make identification easy even in fragmented examples. The allocation of this species to the genus Dinopterygium seems reasonable although the morphology aso suggests affinities with Ctenidodinium and Wanea. This species appears to be a good marker for the Callovian and basal Oxfordian.
Riding, 1987, p. 62
Limbodinium absidatum is distinguished from other forms of Limbodinium (Limbodinium sp., L. cf. L. absidatum), by the often discontinuous nature of the precingular parasutures and the wide, strongly denticulate posterior paracingular flange.