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Impagidinium alectrolophum
Impagidinium alectrolophum (Sarjeant, 1966) Stover and Evitt, 1978
Originally Leptodinium, subsequently (and now) Impagidinium, thirdly Pterodinium.
Below, 1982, transferred this species to Pterodinium Eisenack, 1958. Lentin and Williams, 1985, retained it in Impagidinium.
Holotype: Sarjeant, 1966, pl.15, figs.5-6; Jan du Chene et al., 1986, pl.54, fig.15-16
Locus typicus: Heslerton, England
Stratum typicum: Middle Barremian
Original diagnosis: Sarjeant, 1966, p.134: Leptodinium alectrolophum
A Leptodinium having an ovoidal theca, without apical horn. Tabulation 4", 6", 7c, 5""", 1p, 1""""; plate boundaries bearing high, delicate crests which form slight projections at their points of junction. Sulcus and cingulum both of moderate breadth: sulcus relatively long, extending almost from apex to antapex. Cingular plate 7c roughly diamond-shaped. Apical prominence formed by junction of crests of apical plates.
Dimensions: holotype: overall length 56 µm, breadth 50 µm; shell length 47.5 µm, breadth 42.5 µm; width of cingulum c.5.5 µm. Paratype: overall length 61.5 µm, breadth 54-51 µm; shell length 50 µm, breadth 46 µm; width of cingulum c.6 µm. Other specimens observed were of intermediate dimensions.
Original description: Sarjeant, 1966, p. 135: Leptodinium alectrolophum
Theca ovoidal, an appearance of polygonality being imparted by the crests. The pericoel surface bears a coarse granulation, granules being rather regularly spaced. The crests are thin and high, with minute, inconspicuous perforations. Their distal edge is usually smooth, occasionally finely denticulate; crests of a single individual may in part have smooth, in part denticulate, edges.
The apical prominence appears to be formed solely by the junction of crests bounding the four apical plates; there appears to be no apical horn as such. Apical plate 1" occupies the anterior extension of the sulcus; since the sulcus is long and approaches the apex, plate 1" is proportionately small. The six precingular plates are all quite large. Presence of an anterior intercalary plate was suspected but not confirmed; if present, this plate is relatively small. Five well-developed postcingular plates are present; plate 1""" is reduced to accommodate a quadrate posterior intercalary plate. The antapex is occupied by a single, large plate.
The cingulum forms a strong laevorotatory spiral such that its two ends differ in antero-posterior position by roughly twice its width. There are six clear cingular plates, plus a seventh, diamond-shaped plate, here designated 7c, which lies between the posterior end of the cingulum and the sulcus. The sulcus is narrow and long, extending almost from apex to antapex.
An archaeopyle is not present in the holotype; however, the paratype has a well-developed precingular archaeopyle formed by loss of plate 3".
Affinities:
Sarjeant, 1966, p.135: Leptodinium alectrolophum:
Leptodinium alectrolophum differs from all described species in its combination of crest and thecal morphology and tabulation. It resembles Gonyaulacysta gorngylos in having a seventh polygonal plate at the posterior end of the cingulum, but differs in tabulation and crest form and shape. Heslertonia heslertonense has even higher crests; the surface lacks similar granulation and the tabulation is again different.
In certain orientations, the high crests of this species produce a misleading resemblance to Scriniodinium: however, detailed study shows that no pericoel is present.
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Addition to diagnosis: Heilmann-Clausen and Thomson 1995, p. 300: The cyst is partially suturocavate.
Remarks: Heilmann-Clausen and Thomson 1995, p. 300
The presence of a pericoel at the parasutures is clearly seen in the paratype figured by SARJEANT (1966b, Pl. 15, fig. 3) and in the holotype, as refigured in JAN DU CHENE et al. (1986a, Pl. 54, fig. 16). The cavities are best developed in gonal positions.
The specimens examined in the present study show variable degrees of cavation, ranging from essentially non-cavate specimens, to forms with wall-separation over entire paraplates (Pl. 9, fig. 20). The latter specimens are probably transitional to Pentadinium omasum HARDING, 1990.
The structure and sculpture of the endophragm is variable. Thus the endophragm may contain fine internal vesicles, giving the cysts a characteristic blackish appearance (Pl. 9, fig. 18). Other specimens are non-vesiclar and some of these may be granular.
See also remarks to Pentadinium omasum.
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Originally Leptodinium, subsequently (and now) Impagidinium, thirdly Pterodinium.
Below, 1982, transferred this species to Pterodinium Eisenack, 1958. Lentin and Williams, 1985, retained it in Impagidinium.
Holotype: Sarjeant, 1966, pl.15, figs.5-6; Jan du Chene et al., 1986, pl.54, fig.15-16
Locus typicus: Heslerton, England
Stratum typicum: Middle Barremian
Original diagnosis: Sarjeant, 1966, p.134: Leptodinium alectrolophum
A Leptodinium having an ovoidal theca, without apical horn. Tabulation 4", 6", 7c, 5""", 1p, 1""""; plate boundaries bearing high, delicate crests which form slight projections at their points of junction. Sulcus and cingulum both of moderate breadth: sulcus relatively long, extending almost from apex to antapex. Cingular plate 7c roughly diamond-shaped. Apical prominence formed by junction of crests of apical plates.
Dimensions: holotype: overall length 56 µm, breadth 50 µm; shell length 47.5 µm, breadth 42.5 µm; width of cingulum c.5.5 µm. Paratype: overall length 61.5 µm, breadth 54-51 µm; shell length 50 µm, breadth 46 µm; width of cingulum c.6 µm. Other specimens observed were of intermediate dimensions.
Original description: Sarjeant, 1966, p. 135: Leptodinium alectrolophum
Theca ovoidal, an appearance of polygonality being imparted by the crests. The pericoel surface bears a coarse granulation, granules being rather regularly spaced. The crests are thin and high, with minute, inconspicuous perforations. Their distal edge is usually smooth, occasionally finely denticulate; crests of a single individual may in part have smooth, in part denticulate, edges.
The apical prominence appears to be formed solely by the junction of crests bounding the four apical plates; there appears to be no apical horn as such. Apical plate 1" occupies the anterior extension of the sulcus; since the sulcus is long and approaches the apex, plate 1" is proportionately small. The six precingular plates are all quite large. Presence of an anterior intercalary plate was suspected but not confirmed; if present, this plate is relatively small. Five well-developed postcingular plates are present; plate 1""" is reduced to accommodate a quadrate posterior intercalary plate. The antapex is occupied by a single, large plate.
The cingulum forms a strong laevorotatory spiral such that its two ends differ in antero-posterior position by roughly twice its width. There are six clear cingular plates, plus a seventh, diamond-shaped plate, here designated 7c, which lies between the posterior end of the cingulum and the sulcus. The sulcus is narrow and long, extending almost from apex to antapex.
An archaeopyle is not present in the holotype; however, the paratype has a well-developed precingular archaeopyle formed by loss of plate 3".
Affinities:
Sarjeant, 1966, p.135: Leptodinium alectrolophum:
Leptodinium alectrolophum differs from all described species in its combination of crest and thecal morphology and tabulation. It resembles Gonyaulacysta gorngylos in having a seventh polygonal plate at the posterior end of the cingulum, but differs in tabulation and crest form and shape. Heslertonia heslertonense has even higher crests; the surface lacks similar granulation and the tabulation is again different.
In certain orientations, the high crests of this species produce a misleading resemblance to Scriniodinium: however, detailed study shows that no pericoel is present.
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Addition to diagnosis: Heilmann-Clausen and Thomson 1995, p. 300: The cyst is partially suturocavate.
Remarks: Heilmann-Clausen and Thomson 1995, p. 300
The presence of a pericoel at the parasutures is clearly seen in the paratype figured by SARJEANT (1966b, Pl. 15, fig. 3) and in the holotype, as refigured in JAN DU CHENE et al. (1986a, Pl. 54, fig. 16). The cavities are best developed in gonal positions.
The specimens examined in the present study show variable degrees of cavation, ranging from essentially non-cavate specimens, to forms with wall-separation over entire paraplates (Pl. 9, fig. 20). The latter specimens are probably transitional to Pentadinium omasum HARDING, 1990.
The structure and sculpture of the endophragm is variable. Thus the endophragm may contain fine internal vesicles, giving the cysts a characteristic blackish appearance (Pl. 9, fig. 18). Other specimens are non-vesiclar and some of these may be granular.
See also remarks to Pentadinium omasum.
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