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Ascodinium diversum
Ascodinium diversum, (Davey, 1979), Helenes, 1983
Now Ovoidinium. Originally (and now) Ovoidinium, subsequently Ascodinium. Lentin and Williams, 1989, retained this species in Ovoidinium Davey, 1970.
Holotype: Davey, 1979, pl.6, fig.9
Locus typicus: Northern Bay of Biscay
Stratum typicum: Late Aptian-Early Albian
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Original description as Ovoidinium diversum: [Davey 1979, p. 558]:
Diagnosis:
The cyst is subspherical in shape and composed of a very thick, intraperforate endophragm and a variably developed, thin periphragm. The latter may closely adhere to the endophragm or it may be quite distinct and sometimes forms irregularly shaped protuberances; in the latter case the pericoel is also irregularly developed.
The combination archeopyle, of type 4A3I, is always developed and the operculum often remains attached; endophragm and periphragm always remain attached in the operculum.
Description:
The endophragm is very thick, usually about 4 µm, and is strongly intraperforate which gives the wall a spongy appearance. Rarely, very poorly developed lines on the wall surface partly define a tabulation. Only occasionally does the periphragm adhere so closely to the endophragm
that no pericoel is formed (see Paratype 2). The holotype represents an average specimen in the range of variation in that the thin, wrinkled, hyaline periphragm appears to form a loose enveloping cover around the endocyst. Paratype 2 is an extreme example where the periphragm is well developed but not irregularly, as is normally the case, but forms high extensions over the pre-, postcingular, and antapical paraplates areas. The archeopyle is that typical for the genus and includes the removal of four apical and three intercalary plates as a single unit (Evitt, 1967). The most distinctive characteristic of the archeopyle, which could be mistaken for a simple apical archeopyle (type A), is the straight paraplate boundary parallel to the cingulum on the dorsal surface. This is the boundary between paraplate 2a, included with the operculum, and paraplate 4"".
Dimensions:
Range: Length of endocyst (with operculum): 49-68 µm; Length of endocyst (without operculum): 38-49 µm; Width of endocyst: 38-74 µm; Height of periphragm: 0-14 µm.
Affinities:
The thickness of the endophragm and particularly the irregular development of the periphragm distinguishes O. diversum from all previously described species. In most other species of Ovoidinium the periphragm is relatively consistent in its development and regular apical and antapical pericoels are present. Hence the original concept of Ovoidinium has been modified and more emphasis is now placed on the presence of the unique 4A3I archeopyle type. The most similar species to O. diversum is O.indistinctum (Cookson and Eisenack) Lentin and Williams, 1975, from the Apto-?Albian of Western Australia, which, however, apparently does not have a thick, intraperforate endophragm. The Australian species is also considerably larger - overall length 86-104 µm, overall width 66-96 µm. All other members of this genus are also of mid Cretraceous age.
Now Ovoidinium. Originally (and now) Ovoidinium, subsequently Ascodinium. Lentin and Williams, 1989, retained this species in Ovoidinium Davey, 1970.
Holotype: Davey, 1979, pl.6, fig.9
Locus typicus: Northern Bay of Biscay
Stratum typicum: Late Aptian-Early Albian
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description as Ovoidinium diversum: [Davey 1979, p. 558]:
Diagnosis:
The cyst is subspherical in shape and composed of a very thick, intraperforate endophragm and a variably developed, thin periphragm. The latter may closely adhere to the endophragm or it may be quite distinct and sometimes forms irregularly shaped protuberances; in the latter case the pericoel is also irregularly developed.
The combination archeopyle, of type 4A3I, is always developed and the operculum often remains attached; endophragm and periphragm always remain attached in the operculum.
Description:
The endophragm is very thick, usually about 4 µm, and is strongly intraperforate which gives the wall a spongy appearance. Rarely, very poorly developed lines on the wall surface partly define a tabulation. Only occasionally does the periphragm adhere so closely to the endophragm
that no pericoel is formed (see Paratype 2). The holotype represents an average specimen in the range of variation in that the thin, wrinkled, hyaline periphragm appears to form a loose enveloping cover around the endocyst. Paratype 2 is an extreme example where the periphragm is well developed but not irregularly, as is normally the case, but forms high extensions over the pre-, postcingular, and antapical paraplates areas. The archeopyle is that typical for the genus and includes the removal of four apical and three intercalary plates as a single unit (Evitt, 1967). The most distinctive characteristic of the archeopyle, which could be mistaken for a simple apical archeopyle (type A), is the straight paraplate boundary parallel to the cingulum on the dorsal surface. This is the boundary between paraplate 2a, included with the operculum, and paraplate 4"".
Dimensions:
Range: Length of endocyst (with operculum): 49-68 µm; Length of endocyst (without operculum): 38-49 µm; Width of endocyst: 38-74 µm; Height of periphragm: 0-14 µm.
Affinities:
The thickness of the endophragm and particularly the irregular development of the periphragm distinguishes O. diversum from all previously described species. In most other species of Ovoidinium the periphragm is relatively consistent in its development and regular apical and antapical pericoels are present. Hence the original concept of Ovoidinium has been modified and more emphasis is now placed on the presence of the unique 4A3I archeopyle type. The most similar species to O. diversum is O.indistinctum (Cookson and Eisenack) Lentin and Williams, 1975, from the Apto-?Albian of Western Australia, which, however, apparently does not have a thick, intraperforate endophragm. The Australian species is also considerably larger - overall length 86-104 µm, overall width 66-96 µm. All other members of this genus are also of mid Cretraceous age.