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Oligosphaeridium prolixispinosum
Oligosphaeridium prolixispinosum Davey and Williams, 1966
Originally (and now) Oligosphaeridium, subsequently Tanyosphaeridium.
Duxbury, 1980, transferred this species to Tanyosphaeridium Davey and Williams, 1966. Lentin and Williams, 1981, p.201) retained it in Oligosphaeridium.
Holotype: Davey and Williams, 1966, pl.8, fig.3
Locus typicus: Fetcham Mill, Surrey, England
Stratum typicum: Cenomanian
Original description: Davey and Williams, 1966, p. 76
The periphragm of the central body and of the processes is smooth. The processes are thin-walled and have a fairly broad base up to 8 µm, with characteristic basal wrinkles. There are noticeable circles beneath the processes where only endophragm is present. The processes are about 3 µm in width for most of their length tapering to 2 µm distally before giving rise to the filiform spines. The spines are extremely delicate, 5 to 8 in number, and up to 15 µm in length. The number of processes varies from 16 to 18, the variation probably due to the number of sulcal processes present. In all specimens there is an obvious apical archaeopyle. Surrounding the archaeopyle are 6 precingular processes, then a diastema before the postcingular processes are reached. This diastema marks the position of the cingulum. The processes on the hypotract are difficult to assign to any dinoflagellate tabulation. There is no obvious antapical process, in fact 3 antapical processes usually seem to be present. The reflected tabulation appears to be (4"), 6", 6""", 3"""" and 1-3s.
Dimensions: holotype: overall width 64 µm, diameter of central body 40 by 20 µm, length of processes 18-24 µm, number of processes 17. Range: Length of central body, 33-43 µm, width 20-29 µm, length of processes 18-29 µm.
Supplemental description: Hultberg, 1985, p. 137-138
Chorate cyst, composed of endophragm and periphragm, closely appressed between processes. The surface of both endophragm and periphragm is smooth. The shape of the cyst is subspherical to elongate. Paratabulation is expressed by intratabular processes, formed by the periphragm. The processes are cylindrical in cross-section, hollow, and open distally. The process-tips are trumpet-shaped, with digitate margins. The paratabulation is of gonyaulacacean type, process-formula:
4", 6", 1p, 6""", 1"""". The process, reflecting paraplate 1p, is very small and slender. The paracingular area is devoid of processes. The archeopyle is apical, type tA. Operculum free. Paracingulum and parasulcus are not indicated. Size - 82-125 µm (diameter).
Affinities:
Davey and Williams, 1966, p. 77: O. prolixispinosum sp. nov. is easily distinguishable from other species by its elongate form and small number of processes with very characteristic distal terminations. It should be noted that the basal wrinkles recorded in this species have also been seen in Hystrichosphaeridium bowerbanki.
At the base of the Cenomanian there have been found, together with normal examples of 0. prolixispinosum, two specimens, which possess exactly the same elongate central body and type of processes but there are present 22 and 25 processes. This unusual number is caused by the presence of 6 cingular processes. It would thus appear that 0. prolixispinosum is, in the Lower Cenomanian, rather an unstable species and not until later in the Cenomanian does it settle down, the cingular processes being absent.
Because of the above variation this species is rather difficult to classify since although the cingular processes are absent, it seems to be related to, or maybe even evolved from, a type possessing these processes. Two other factors are that the processes strongly resemble those found in H. bowerbanki and there may be 3 antapical processes present although this is uncertain. Until further information is available this species has been tentatively placed in the genus Oligosphaeridium because of the absence of cingular processes.
Originally (and now) Oligosphaeridium, subsequently Tanyosphaeridium.
Duxbury, 1980, transferred this species to Tanyosphaeridium Davey and Williams, 1966. Lentin and Williams, 1981, p.201) retained it in Oligosphaeridium.
Holotype: Davey and Williams, 1966, pl.8, fig.3
Locus typicus: Fetcham Mill, Surrey, England
Stratum typicum: Cenomanian
Original description: Davey and Williams, 1966, p. 76
The periphragm of the central body and of the processes is smooth. The processes are thin-walled and have a fairly broad base up to 8 µm, with characteristic basal wrinkles. There are noticeable circles beneath the processes where only endophragm is present. The processes are about 3 µm in width for most of their length tapering to 2 µm distally before giving rise to the filiform spines. The spines are extremely delicate, 5 to 8 in number, and up to 15 µm in length. The number of processes varies from 16 to 18, the variation probably due to the number of sulcal processes present. In all specimens there is an obvious apical archaeopyle. Surrounding the archaeopyle are 6 precingular processes, then a diastema before the postcingular processes are reached. This diastema marks the position of the cingulum. The processes on the hypotract are difficult to assign to any dinoflagellate tabulation. There is no obvious antapical process, in fact 3 antapical processes usually seem to be present. The reflected tabulation appears to be (4"), 6", 6""", 3"""" and 1-3s.
Dimensions: holotype: overall width 64 µm, diameter of central body 40 by 20 µm, length of processes 18-24 µm, number of processes 17. Range: Length of central body, 33-43 µm, width 20-29 µm, length of processes 18-29 µm.
Supplemental description: Hultberg, 1985, p. 137-138
Chorate cyst, composed of endophragm and periphragm, closely appressed between processes. The surface of both endophragm and periphragm is smooth. The shape of the cyst is subspherical to elongate. Paratabulation is expressed by intratabular processes, formed by the periphragm. The processes are cylindrical in cross-section, hollow, and open distally. The process-tips are trumpet-shaped, with digitate margins. The paratabulation is of gonyaulacacean type, process-formula:
4", 6", 1p, 6""", 1"""". The process, reflecting paraplate 1p, is very small and slender. The paracingular area is devoid of processes. The archeopyle is apical, type tA. Operculum free. Paracingulum and parasulcus are not indicated. Size - 82-125 µm (diameter).
Affinities:
Davey and Williams, 1966, p. 77: O. prolixispinosum sp. nov. is easily distinguishable from other species by its elongate form and small number of processes with very characteristic distal terminations. It should be noted that the basal wrinkles recorded in this species have also been seen in Hystrichosphaeridium bowerbanki.
At the base of the Cenomanian there have been found, together with normal examples of 0. prolixispinosum, two specimens, which possess exactly the same elongate central body and type of processes but there are present 22 and 25 processes. This unusual number is caused by the presence of 6 cingular processes. It would thus appear that 0. prolixispinosum is, in the Lower Cenomanian, rather an unstable species and not until later in the Cenomanian does it settle down, the cingular processes being absent.
Because of the above variation this species is rather difficult to classify since although the cingular processes are absent, it seems to be related to, or maybe even evolved from, a type possessing these processes. Two other factors are that the processes strongly resemble those found in H. bowerbanki and there may be 3 antapical processes present although this is uncertain. Until further information is available this species has been tentatively placed in the genus Oligosphaeridium because of the absence of cingular processes.