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Ovoidinium incomptum
Ovoidinium incomptum Duxbury 1983
Originally (and now) Ovoidinium, subsequently Ascodinium.
Lentin and Williams, 1985, transferred this species to Ascodinium Cookson and Eisenack, 1960. Lentin and Williams, 1989, retained it in Ovoidinium.
Holotype: Duxbury, 1983, pl.10, figs.5,9, text-fig.30
Locus typicus: Redcliff section, Isle of Wight, England
Stratum typicum: Aptian
Original diagnosis: Duxbury, 1983, p. 64
A small, thin-walled peridiniacean cyst species which is ovoidal and dorso-ventrally flattened. A low, distally rounded and closed apical projection is present and a small apical horn, composed entirely of periphragm may be superimposed on this. A similar, small left antapical horn is invariably present and this small scale posterior cornucavation may be extended so that slight separation of the whole posterior portion of the cyst into two layers may occur. A tAtI archeopyle is observed and the operculum only rarely remains attached. The paracingulum is usually indicated by surface folding, as are some parasutures. Observed Dimensions: Holotype - 52 x 58 Ám. Overall - 61 (49) 38 x 61 (49) 41 µm.
Affinities:
Duxbury, 1983, p. 64: This species is similar to Ovoidinium incorporeum Duxbury but differs in lacking any overt cavation.
O. incomptum differs from O. diversum Davey, 1979 in having a thin endophragm. The latter was described by Davey (1979a, p. 558) as possessing "a very thick, intraperforate endophragm". Also, the maximum development of pericoels in O. incomptum is confined to slight antapical separation of the body layers. There is no indication of the usual situation in O. diversum where the periphragm is "quite distinct and sometimes forms irregularly shaped protuberances."
Originally (and now) Ovoidinium, subsequently Ascodinium.
Lentin and Williams, 1985, transferred this species to Ascodinium Cookson and Eisenack, 1960. Lentin and Williams, 1989, retained it in Ovoidinium.
Holotype: Duxbury, 1983, pl.10, figs.5,9, text-fig.30
Locus typicus: Redcliff section, Isle of Wight, England
Stratum typicum: Aptian
Original diagnosis: Duxbury, 1983, p. 64
A small, thin-walled peridiniacean cyst species which is ovoidal and dorso-ventrally flattened. A low, distally rounded and closed apical projection is present and a small apical horn, composed entirely of periphragm may be superimposed on this. A similar, small left antapical horn is invariably present and this small scale posterior cornucavation may be extended so that slight separation of the whole posterior portion of the cyst into two layers may occur. A tAtI archeopyle is observed and the operculum only rarely remains attached. The paracingulum is usually indicated by surface folding, as are some parasutures. Observed Dimensions: Holotype - 52 x 58 Ám. Overall - 61 (49) 38 x 61 (49) 41 µm.
Affinities:
Duxbury, 1983, p. 64: This species is similar to Ovoidinium incorporeum Duxbury but differs in lacking any overt cavation.
O. incomptum differs from O. diversum Davey, 1979 in having a thin endophragm. The latter was described by Davey (1979a, p. 558) as possessing "a very thick, intraperforate endophragm". Also, the maximum development of pericoels in O. incomptum is confined to slight antapical separation of the body layers. There is no indication of the usual situation in O. diversum where the periphragm is "quite distinct and sometimes forms irregularly shaped protuberances."