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Cribroperidinium undoryense
Cribroperidinium undoryense Smith and Harding, 2004, p.374-375, pl.3, figs.1-6; pl.6, figs.7-9; text-fig.6.
Holotype: Smith and Harding, 2004, pl.3, figs.1-3.
Age: Mid Volgian.
Holotype: Slide U24/2, England Finder coordinates J47/1. Sedgwick Museum number X.39369 ( Plate III, 1–3).
Paratype: Slide U24/2, England Finder coordinates J40/2. Sedgwick Museum number X.39370 ( Plate III, 4–6).
Type locality: Gorodische section, Volga Basin.
Type horizon: Bed 16 conglomerate (sample U24), Middle Volgian, Virgatites virgatus Zone.
Range: Mid-Volgian (see Fig. 8).
Etymology: named after the town of Undory, close to the Gorodische section.
Diagnosis: elongate, proximate acavate cribroperidinioid cyst with a narrow diamond-shaped ambitus and long robust, distally tapering apical horn. Differentiated autophragm is densely pitted or spongy, and sculpted into high fenestrate sutural septa which are highest at the cingulum. Distal edges of the septa are smooth to undulose or occasionally irregular. Tabulation is cribroperidinioid, with cingular, sulcal, first postcingular and posterior intercalary plates being suppressed.
Description: elongate, prolate diamond-shaped ambitus, both episome and hyposome are narrowly conical to bell-shaped with rounded apical extremities, and of approximately equal size (the cingulum descends from dorsal to ventral surfaces, so that the hypocyst is larger than the epicyst on the dorsal surface). Cyst proximate, acavate. Differentiated autophragm appears densely pitted on the surface and micro-vacuolate in section. The apex bears a long, robust, distally-tapering solid horn. The autophragm is sculpted into fenestrate sutural septa. The height of these septa is variable, but cingular septa are always the highest (9.1–15 μm). Height of the pre- and post-cingular septa is greatest adjacent to the cingulum and in regions close to the apices. Sutural septa at the antapex (6.5–13 μm) tend to be higher than those at the apex. Distal margins of the sutural septa are generally smooth to undulose, but may be irregular in poorly preserved specimens. Spine-like projections are often apparent at gonal areas, typically at junctions of the post-cingular plate homologues with plate 1⁗, and pre-cingular series with the apical plate homologues. These projections result from the fusion of sutural septa, the height of which may also be enlarged at such plate junctions.
Tabulation formula: 4′, 6″, ?c, ?s, 5‴, ?1p, 1⁗, with a cribroperidinioidean arrangement, showing dextral torsion and an L-type ventral organisation (Fig. 6). The first and fourth (*1′ and *4′) apical plate homologues are narrow and elongate: both are approximately parallel-sided near the sulcus, but broaden towards the apex. Plate 6″ is of reduced size in comparison to the other precingular plates, and is approximately deltoidal in shape with a geniculate anterior margin. The boundary of this plate with *1′ is narrow and indistinct. The archeopyle is Type P, formed from the complete loss of plate 3″. The archeopyle is pentagonal to ovoidal, generally with a rounded anterior margin, the operculum being somewhat reduced.
The cingulum is narrow and helicoid, descends to a variable extent from posterior to anterior surfaces, and is offset at the sulcus by 4–5 cingular widths. Cingular plates have not been determined. The anterior part of the sulcal region extends a short way above the apical edge of the cingulum. Cingular, sulcal, first postcingular and posterior intercalary tabulation is suppressed.
Postcingular plate homologues *2‴ and *6‴ are quadrate or broadly triangular, taper towards the antapex, and are of reduced but approximately equal size. By contrast plate homologues *3‴ to *5‴ are much larger, with *4‴ and *5‴ being the largest plates on the hypocyst. The antapical plate is displaced ventrally so that only its boundary with plate homologue *4‴ meets the antapex. It is bounded by the sulcus and postcingular plate homologues *3‴ to *6‴, and is thus asymmetrical on the ventral surface.
Dimensions: length (antapex to base of horn): (55) 60 (70) μm; width at cingulum (36) 40 (49) μm; horn length (5) 14 (18) μm. 6 specimens measured from samples U21 and U24.
Remarks: this taxon is closely comparable to Cribroperidinium magnificum. However, it differs in having more angular and conical episomal and hyposomal regions, by the much longer apical horn, and to a lesser extent by the more strongly offset cingulum. In addition, the septa are more ‘solid’ and fenestrate in appearance rather than truly erymnate. C. undoryensis also differs from C. sepimentum Neale and Sarjeant 1962 and C. boreas Davey emend. Helenes 1985b, by its more angular and biconical ambitus, and from C. cornutum Davey 1974, as the apical horn of the latter is hollow and formed by an extreme separation of the layers in the differentiated autophragm. Although C. murochoratum Dűrr 1987 possesses high sutural septa, it differs from C. undoryensis in its low episome and very reduced apical horn. The ambitus of C. undoryensis is quite different from those of C. granulatum Klement emend. Stover and Evitt 1978, C. granuligerum (Klement) Stover and Evitt 1978 and C. globatum Gitmez and Sarjeant emend. Helenes 1984b in being much more axially elongate and angular. C. martonense Bailey et al., 1997 differs in having a prominent but hollow apical horn and less regularly developed sutural crests.
Cribroperidinium undoryensis further differs from Rhychodiniopsis fimbriata Duxbury emend. Jan du Chêne et al., 1985 by having a solid apical horn formed as an extension from the autophragm, rather than a hollow conical horn formed from tapering of the autophragm at the apex. Also by having a more strongly helical cingulum, and by the suppression of the posterior intercalary plate in C. undoryensis. The new taxon also contrasts with R. pennata Riley in Fisher and Riley, 1980 emend. Jan du Chêne et al., 1985 in having a much less rounded cyst outline, much longer and more robust apical horn, and in the development of higher, more elaborate sutural septa, particularly at the cingulum. C. undoryensis further differs from species of Rhynchodiniopsis Deflandre emend. Jan du Chêne et al., 1985 as the antapical plate is not quadrate and is ‘displaced’ onto the ventral surface.
Holotype: Smith and Harding, 2004, pl.3, figs.1-3.
Age: Mid Volgian.
Holotype: Slide U24/2, England Finder coordinates J47/1. Sedgwick Museum number X.39369 ( Plate III, 1–3).
Paratype: Slide U24/2, England Finder coordinates J40/2. Sedgwick Museum number X.39370 ( Plate III, 4–6).
Type locality: Gorodische section, Volga Basin.
Type horizon: Bed 16 conglomerate (sample U24), Middle Volgian, Virgatites virgatus Zone.
Range: Mid-Volgian (see Fig. 8).
Etymology: named after the town of Undory, close to the Gorodische section.
Diagnosis: elongate, proximate acavate cribroperidinioid cyst with a narrow diamond-shaped ambitus and long robust, distally tapering apical horn. Differentiated autophragm is densely pitted or spongy, and sculpted into high fenestrate sutural septa which are highest at the cingulum. Distal edges of the septa are smooth to undulose or occasionally irregular. Tabulation is cribroperidinioid, with cingular, sulcal, first postcingular and posterior intercalary plates being suppressed.
Description: elongate, prolate diamond-shaped ambitus, both episome and hyposome are narrowly conical to bell-shaped with rounded apical extremities, and of approximately equal size (the cingulum descends from dorsal to ventral surfaces, so that the hypocyst is larger than the epicyst on the dorsal surface). Cyst proximate, acavate. Differentiated autophragm appears densely pitted on the surface and micro-vacuolate in section. The apex bears a long, robust, distally-tapering solid horn. The autophragm is sculpted into fenestrate sutural septa. The height of these septa is variable, but cingular septa are always the highest (9.1–15 μm). Height of the pre- and post-cingular septa is greatest adjacent to the cingulum and in regions close to the apices. Sutural septa at the antapex (6.5–13 μm) tend to be higher than those at the apex. Distal margins of the sutural septa are generally smooth to undulose, but may be irregular in poorly preserved specimens. Spine-like projections are often apparent at gonal areas, typically at junctions of the post-cingular plate homologues with plate 1⁗, and pre-cingular series with the apical plate homologues. These projections result from the fusion of sutural septa, the height of which may also be enlarged at such plate junctions.
Tabulation formula: 4′, 6″, ?c, ?s, 5‴, ?1p, 1⁗, with a cribroperidinioidean arrangement, showing dextral torsion and an L-type ventral organisation (Fig. 6). The first and fourth (*1′ and *4′) apical plate homologues are narrow and elongate: both are approximately parallel-sided near the sulcus, but broaden towards the apex. Plate 6″ is of reduced size in comparison to the other precingular plates, and is approximately deltoidal in shape with a geniculate anterior margin. The boundary of this plate with *1′ is narrow and indistinct. The archeopyle is Type P, formed from the complete loss of plate 3″. The archeopyle is pentagonal to ovoidal, generally with a rounded anterior margin, the operculum being somewhat reduced.
The cingulum is narrow and helicoid, descends to a variable extent from posterior to anterior surfaces, and is offset at the sulcus by 4–5 cingular widths. Cingular plates have not been determined. The anterior part of the sulcal region extends a short way above the apical edge of the cingulum. Cingular, sulcal, first postcingular and posterior intercalary tabulation is suppressed.
Postcingular plate homologues *2‴ and *6‴ are quadrate or broadly triangular, taper towards the antapex, and are of reduced but approximately equal size. By contrast plate homologues *3‴ to *5‴ are much larger, with *4‴ and *5‴ being the largest plates on the hypocyst. The antapical plate is displaced ventrally so that only its boundary with plate homologue *4‴ meets the antapex. It is bounded by the sulcus and postcingular plate homologues *3‴ to *6‴, and is thus asymmetrical on the ventral surface.
Dimensions: length (antapex to base of horn): (55) 60 (70) μm; width at cingulum (36) 40 (49) μm; horn length (5) 14 (18) μm. 6 specimens measured from samples U21 and U24.
Remarks: this taxon is closely comparable to Cribroperidinium magnificum. However, it differs in having more angular and conical episomal and hyposomal regions, by the much longer apical horn, and to a lesser extent by the more strongly offset cingulum. In addition, the septa are more ‘solid’ and fenestrate in appearance rather than truly erymnate. C. undoryensis also differs from C. sepimentum Neale and Sarjeant 1962 and C. boreas Davey emend. Helenes 1985b, by its more angular and biconical ambitus, and from C. cornutum Davey 1974, as the apical horn of the latter is hollow and formed by an extreme separation of the layers in the differentiated autophragm. Although C. murochoratum Dűrr 1987 possesses high sutural septa, it differs from C. undoryensis in its low episome and very reduced apical horn. The ambitus of C. undoryensis is quite different from those of C. granulatum Klement emend. Stover and Evitt 1978, C. granuligerum (Klement) Stover and Evitt 1978 and C. globatum Gitmez and Sarjeant emend. Helenes 1984b in being much more axially elongate and angular. C. martonense Bailey et al., 1997 differs in having a prominent but hollow apical horn and less regularly developed sutural crests.
Cribroperidinium undoryensis further differs from Rhychodiniopsis fimbriata Duxbury emend. Jan du Chêne et al., 1985 by having a solid apical horn formed as an extension from the autophragm, rather than a hollow conical horn formed from tapering of the autophragm at the apex. Also by having a more strongly helical cingulum, and by the suppression of the posterior intercalary plate in C. undoryensis. The new taxon also contrasts with R. pennata Riley in Fisher and Riley, 1980 emend. Jan du Chêne et al., 1985 in having a much less rounded cyst outline, much longer and more robust apical horn, and in the development of higher, more elaborate sutural septa, particularly at the cingulum. C. undoryensis further differs from species of Rhynchodiniopsis Deflandre emend. Jan du Chêne et al., 1985 as the antapical plate is not quadrate and is ‘displaced’ onto the ventral surface.