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Yalkalpodinium elangianum
Yalkalpodinium elangianum Riding and Helby, 2001d, p.101–102
Holotype: Riding and Helby, 2001d, figs.20I–K.
Age: late Callovian–Oxfordian.
Original description: Riding & Helby, 2001d:
A species of Yalkalpodinium, which is slightly dorsoventrally flattened, intermediate in size and ellipsoidal to subcircular in outline. Endophragm relatively thick, psilate, occasionally sporadically granulate to baculate where the endophragm and periphragm are separated. The endophragm may or may not bear rare slender, solid processes which connect to the interior of the periphragm at the cyst periphery. Periphragm thin, microreticulate; rarely microscabrate. One or two ovoidal claustra may be present in the periphragm at the antapex. Standard sexiform gonyaulacalean paratabulation indicated by low smooth folds or ridges in the periphragm. The periphragm at the paracingulum is sometimes indented and the longitudinal parasulcus is narrow and deeply indented. The operculum is compound.
Dimensions (µm; n=38) Min. (Mean) Max.
Length of pericyst (incl. operculum): 67 (73) 80
Length of pericyst (excl. operculum): 56 (66) 75
Length of endocyst (incl. operculum): 63 (67) 74
Length of endocyst (excl. operculum): 46 (58) 68
Width of pericyst: 56 (68) 79
Width of endocyst: 47 (60) 72
Affinities/Comparison:
Yalkalpodinium elangiana differs from the genotype, Y. scutum Morgan 1980, in not exhibiting paracingular protrusions and in having sporadically ornamented endophragm, microreticulate periphragm, being paratabulate, of intermediate size and having a compound operculum. Yalkalpodinium indicum (Jain & Taugourdeau-Lanz 1973) Morgan 1980 is similar in morphology to Y. scutum, but has a small apical horn. The species Ambonosphaera hemicavata Prauss 1989 is similar in overall morphology and size to Yalkalpodinium elangiana. However, A. hemicavata is bicavate and significantly more longitudinally elongate. The parasulcus in A. hemicavata is relatively wide and prominent, with several small claustra inserted around the antapical parasulcal paraplate. Furthermore, Prauss (1989) described the endophragm of A. hemicavata as being 'fossulate, alveolate as well as rugulate to baculate' (translation). The endophragm of Y. elangiana is never fossulate (grooved) or alveolate (punctoreticulate). Morgan (1980) transfereed the Tithonian Cyclonephelium areolatum Cookson & Eisenack 1960 to Yalkalpodinium. However, this was rejected by Stover & Williams (1987, p. 231) as, in their opinion, this taxon is questionably cavate and lenticular. We disagree with Stover & Williams (1987) as the holotype and our topotype material show indisputable cavation. However, we suggest a provisional transfer to Yalkalpodinium on the basis that we have seen no evidence of claustra. Furthermore, in Y? areolatum the endophragm bears many more periphragm support structures than in Y. elangiana, and the condition approaches holocavation. .The other two unequivocal species of Yalkalpodinium, Y. indicum and Y. scutum are both Early Cretaceous (Neocomian-Albian) Indo-Pacific species and may be conspecific.
Comments. The apical archaeopyle in this species has normally operated and the resulting prominent midventral parasulcal notch, formed by the loss of the relatively large 1' paraplate, is a characteristc feature. The operculum appears to be compound; the 1' paraplate frequently is observed detached from both the loisthocyst and the other apical paraplates. Specimens of Yalkalpodinium elangiana may rarely have thin, solid processes inserted between the cyst wall layers in the peripheral regions in both hemispheres. These processes are not consistently and/or extensively developed and therefore the species is deemed to be circumcavate and not holocavate. The periphragm is microreticulate to occasionally microscabrate; it encloses a pericoel which is usually best developed on the hypocyst and is typically 5-6 µm wide. The lacunae in the periphragm have widely differing concentrations, for example they are often relatively sparse in the middorsal and midventral areas. They are also virtually absent in the paracingulum and parasulcus. By contrast, they may be relatively densely inserted in the peripheral areas of the cyst. The lacunae are normally between 1 and 2 µm in diameter. One, occasionally two, ovoidal claustra may penetrate the periphragm at the antapex. Claustra are also present in the genotype, Yalkalpodinium scutum (see Morgan, 1980. pl31, figs 15-18). The two cyst layers are in contact over most of the dorsal and ventral areas, and there is a distinct border marking wall separation approaching the cyst periphery. The species may exhibit one or more dark, subspherical accumulation bodies within the endocoel of the cyst, normally close to the paracingular area. The paracingulum is essentially equatorial in position, however the hypocyst may be slightly longer than the epicyst.
Holotype: Riding and Helby, 2001d, figs.20I–K.
Age: late Callovian–Oxfordian.
Original description: Riding & Helby, 2001d:
A species of Yalkalpodinium, which is slightly dorsoventrally flattened, intermediate in size and ellipsoidal to subcircular in outline. Endophragm relatively thick, psilate, occasionally sporadically granulate to baculate where the endophragm and periphragm are separated. The endophragm may or may not bear rare slender, solid processes which connect to the interior of the periphragm at the cyst periphery. Periphragm thin, microreticulate; rarely microscabrate. One or two ovoidal claustra may be present in the periphragm at the antapex. Standard sexiform gonyaulacalean paratabulation indicated by low smooth folds or ridges in the periphragm. The periphragm at the paracingulum is sometimes indented and the longitudinal parasulcus is narrow and deeply indented. The operculum is compound.
Dimensions (µm; n=38) Min. (Mean) Max.
Length of pericyst (incl. operculum): 67 (73) 80
Length of pericyst (excl. operculum): 56 (66) 75
Length of endocyst (incl. operculum): 63 (67) 74
Length of endocyst (excl. operculum): 46 (58) 68
Width of pericyst: 56 (68) 79
Width of endocyst: 47 (60) 72
Affinities/Comparison:
Yalkalpodinium elangiana differs from the genotype, Y. scutum Morgan 1980, in not exhibiting paracingular protrusions and in having sporadically ornamented endophragm, microreticulate periphragm, being paratabulate, of intermediate size and having a compound operculum. Yalkalpodinium indicum (Jain & Taugourdeau-Lanz 1973) Morgan 1980 is similar in morphology to Y. scutum, but has a small apical horn. The species Ambonosphaera hemicavata Prauss 1989 is similar in overall morphology and size to Yalkalpodinium elangiana. However, A. hemicavata is bicavate and significantly more longitudinally elongate. The parasulcus in A. hemicavata is relatively wide and prominent, with several small claustra inserted around the antapical parasulcal paraplate. Furthermore, Prauss (1989) described the endophragm of A. hemicavata as being 'fossulate, alveolate as well as rugulate to baculate' (translation). The endophragm of Y. elangiana is never fossulate (grooved) or alveolate (punctoreticulate). Morgan (1980) transfereed the Tithonian Cyclonephelium areolatum Cookson & Eisenack 1960 to Yalkalpodinium. However, this was rejected by Stover & Williams (1987, p. 231) as, in their opinion, this taxon is questionably cavate and lenticular. We disagree with Stover & Williams (1987) as the holotype and our topotype material show indisputable cavation. However, we suggest a provisional transfer to Yalkalpodinium on the basis that we have seen no evidence of claustra. Furthermore, in Y? areolatum the endophragm bears many more periphragm support structures than in Y. elangiana, and the condition approaches holocavation. .The other two unequivocal species of Yalkalpodinium, Y. indicum and Y. scutum are both Early Cretaceous (Neocomian-Albian) Indo-Pacific species and may be conspecific.
Comments. The apical archaeopyle in this species has normally operated and the resulting prominent midventral parasulcal notch, formed by the loss of the relatively large 1' paraplate, is a characteristc feature. The operculum appears to be compound; the 1' paraplate frequently is observed detached from both the loisthocyst and the other apical paraplates. Specimens of Yalkalpodinium elangiana may rarely have thin, solid processes inserted between the cyst wall layers in the peripheral regions in both hemispheres. These processes are not consistently and/or extensively developed and therefore the species is deemed to be circumcavate and not holocavate. The periphragm is microreticulate to occasionally microscabrate; it encloses a pericoel which is usually best developed on the hypocyst and is typically 5-6 µm wide. The lacunae in the periphragm have widely differing concentrations, for example they are often relatively sparse in the middorsal and midventral areas. They are also virtually absent in the paracingulum and parasulcus. By contrast, they may be relatively densely inserted in the peripheral areas of the cyst. The lacunae are normally between 1 and 2 µm in diameter. One, occasionally two, ovoidal claustra may penetrate the periphragm at the antapex. Claustra are also present in the genotype, Yalkalpodinium scutum (see Morgan, 1980. pl31, figs 15-18). The two cyst layers are in contact over most of the dorsal and ventral areas, and there is a distinct border marking wall separation approaching the cyst periphery. The species may exhibit one or more dark, subspherical accumulation bodies within the endocoel of the cyst, normally close to the paracingular area. The paracingulum is essentially equatorial in position, however the hypocyst may be slightly longer than the epicyst.