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Cepadinium variabile
Cepadinium variabilis, Duxbury, 1983
This species, the original type of the genus Cepadinium, was considered to be a tax. synonym of Cepadinium ventriosum (Alberti, 1959) Lister and Batten, 1988, by Lister and Batten, 1988. Since Cepadinium ventriosum is the taxonomic senior synonym, it is the correct name for the type species of Cepadinium, but the nomenclatural type of the genus remains the holotype of Cepadinium variabile.
Holotype: Duxbury, 1983, pl.9, fig.8, text-figs.27A-E
Locus typicus: Atherfield section, Isle of Wight, England
Stratum typicum: Early Aptian
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Original description: [Duxbury, 1983, p. 58-59]:
Diagnosis:
A proximo-cavate dinoflagellate cyst possessing well-developed apical and left-antapical horns and a right-antapical horn which is reduced to varying degrees. Four body layers are present in the most completely preserved specimens but more commonly only three are observed. In each of these cases, a granular and/or conical body ornament is present on the second layer in. Two body layers may be observed in extreme cases, in which event the ornament is observed on the outer layer. A laevorotatory paracingulum is always present, as is a ventral depression which may contain a poorly-defined rostrum.
The archeopyle is of a 3A(2"-4")3I type and the operculum usually remains attached ventrally.
No paratabulation other that that reflected by the paracingulum and archeopyle margin has been observed.
Observed Dimensions:
Holotype (four-layered) - 73 x 58 µm.
Overall - 87 (67) 46 x 64 (49) 42 µm.
Affinities:
This species is most distinctive and easily recognisable. The variation in the number of body layers is remarkable and, as noted above, results in specimens possessing anything from two to four body layers (see Text-Figs. 27 and 28). As is shown in Text-Fig. 27, the outline of the four body layers becomes more pronouncedly peridiniacean towards the exterior of the cyst. Specimens possessing four body layers are rare but those with three are fairly abundant and it is noteworthy that in both the four-layered and the three-layered forms, the granular/conical body ornament is observed on the second layer in (designated Mesophragm 2 in Text-Fig. 27). The two layered specimens possess ornament on the outer layer. On the evidence afforded by the very ornamented layer in C. variabilis, it may be inferred that the three-layered specimens differ from the four-layered ones in lacking the endophragm (as defined in Text-Fig. 27) whilst the two-layered forms also lack the periphragm (again as defined in Text-Fig. 27).
"Canningia" turrita Brideaux, 1977 is most reminiscent of the two-layered forms of C. variabilis, particularly in the archeopyle type. Brideaux states (1977, p. 13), "Archeopyle interpreted as being formed by the loss of at least three apical paraplates (probably 2"-4") and one or three intercalary paraplates (la or la-3a)", and this is very similar to that inferred for C. variabilis (3A(2"-4")3I). From his further remarks on "C." turrita, Brideaux may be seen to consider his species as possibly related to the peridinoid lineage and again this suggests some comparability with C. variabilis. Brideaux has, however, stated (pers. comm.) that he has not observed "C." turrita other than in the type area (Richardson Mountains, District of Mackenzie, Canada) and that "C." turrita never exhibited any wall layers other than those discussed in Brideaux, 1977 (thin, smooth endophragm and thin periphragm with scattered grana or coni). C. variabilis is here considered a new species but the similarity between it and "C." turrita must be recognised, particularly in the mode of archeopyle formation.
This species, the original type of the genus Cepadinium, was considered to be a tax. synonym of Cepadinium ventriosum (Alberti, 1959) Lister and Batten, 1988, by Lister and Batten, 1988. Since Cepadinium ventriosum is the taxonomic senior synonym, it is the correct name for the type species of Cepadinium, but the nomenclatural type of the genus remains the holotype of Cepadinium variabile.
Holotype: Duxbury, 1983, pl.9, fig.8, text-figs.27A-E
Locus typicus: Atherfield section, Isle of Wight, England
Stratum typicum: Early Aptian
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Duxbury, 1983, p. 58-59]:
Diagnosis:
A proximo-cavate dinoflagellate cyst possessing well-developed apical and left-antapical horns and a right-antapical horn which is reduced to varying degrees. Four body layers are present in the most completely preserved specimens but more commonly only three are observed. In each of these cases, a granular and/or conical body ornament is present on the second layer in. Two body layers may be observed in extreme cases, in which event the ornament is observed on the outer layer. A laevorotatory paracingulum is always present, as is a ventral depression which may contain a poorly-defined rostrum.
The archeopyle is of a 3A(2"-4")3I type and the operculum usually remains attached ventrally.
No paratabulation other that that reflected by the paracingulum and archeopyle margin has been observed.
Observed Dimensions:
Holotype (four-layered) - 73 x 58 µm.
Overall - 87 (67) 46 x 64 (49) 42 µm.
Affinities:
This species is most distinctive and easily recognisable. The variation in the number of body layers is remarkable and, as noted above, results in specimens possessing anything from two to four body layers (see Text-Figs. 27 and 28). As is shown in Text-Fig. 27, the outline of the four body layers becomes more pronouncedly peridiniacean towards the exterior of the cyst. Specimens possessing four body layers are rare but those with three are fairly abundant and it is noteworthy that in both the four-layered and the three-layered forms, the granular/conical body ornament is observed on the second layer in (designated Mesophragm 2 in Text-Fig. 27). The two layered specimens possess ornament on the outer layer. On the evidence afforded by the very ornamented layer in C. variabilis, it may be inferred that the three-layered specimens differ from the four-layered ones in lacking the endophragm (as defined in Text-Fig. 27) whilst the two-layered forms also lack the periphragm (again as defined in Text-Fig. 27).
"Canningia" turrita Brideaux, 1977 is most reminiscent of the two-layered forms of C. variabilis, particularly in the archeopyle type. Brideaux states (1977, p. 13), "Archeopyle interpreted as being formed by the loss of at least three apical paraplates (probably 2"-4") and one or three intercalary paraplates (la or la-3a)", and this is very similar to that inferred for C. variabilis (3A(2"-4")3I). From his further remarks on "C." turrita, Brideaux may be seen to consider his species as possibly related to the peridinoid lineage and again this suggests some comparability with C. variabilis. Brideaux has, however, stated (pers. comm.) that he has not observed "C." turrita other than in the type area (Richardson Mountains, District of Mackenzie, Canada) and that "C." turrita never exhibited any wall layers other than those discussed in Brideaux, 1977 (thin, smooth endophragm and thin periphragm with scattered grana or coni). C. variabilis is here considered a new species but the similarity between it and "C." turrita must be recognised, particularly in the mode of archeopyle formation.