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Oligosphaeridium intermedium
Oligosphaeridium intermedium Corradini, 1973
Holotype: Corradini, 1973, pl.21, fig.7, text-fig.6
Locus typicus: Mt. Aldone, Piacenza, Italy
Stratum typicum: Late Cretaceous-?Palaeocene
Original diagnosis: Corradini, 1973, p. 143
Chorate cyst with subspherical to ovoidal central body composed of thin, smooth endophragm and periphragm. Length of processes like or exceeding the diameter of the central body. Tubiform processes slightly constricted near their apex and expanded distally in aculeate margins.
Apical archeopyle tetratabular.
Dimensions--Holotype: diameter of the central body 32x34 µm, length of the processes 25-36 µm. Range: diameter of the central body 30-(37)-42 µm, length of the processes 20(30)38 µm, length of the distal spines 4-6 µm.
Original description: Corradini, 1973, p. 143
From the thin, smooth periphragm arise hollow, tubiform processes, one per plate area, slightly tapering distally. Distal margin terminating in a rosette of orthogonal short spines which are 5 to 8 in number. The processes on a specimen do not vary a great deal in their length or width. Sulcal processes not ptesent. Reflected tabulation 4", 6", 6""", 1p, 1"""".
Affinities:
Corradini, 1973, p. 143: The new species may be regarded as an intermediate species between O. buciniferum and O. complex. These chiefly differ in the distal structure of the processes. The first one is characterized by having an entire margin, the second by the numerous and complex appendages. Another intermediate species may be O. asterigerum (Gocht) but the distal spines of its processes are longer than by O. intermedium and occur around the processes more irregularly. Furthermore they are not so complex as shown by the appendages of O. complex. Slight differences occur also between the processes of O. complex and O. pulcherrimum. It is quite evident that just one character (shape of terminal spines) cannot be taken into account to differentiate so many species.
The study of my material clearly shows that transitional forms exist which may be erected to a specific level. Pending a revision on such group of forms, I prefer to follow the majority of the authors, who consider all these species as valid, also for the stratigraphical value they apparently have. O. prolixispinosum Davey & Williams is distinghuished from O. intermedium by a very elongated central body, thinner processes, and by having one or more sulcal processes. Taking into account the number of processes, it seems that some forms, previously related to other genera, belong to the new species. This is the case for some specimens reported by Valensi (1955) as Hystrichosphaeridium tubiferum and for that illustrated by Gorka (1963) as H. asterigerum. These forms, in fact, don"t have the high number of processes typical of Ilystrichosphaeridium, and lack the cingular ones.
Holotype: Corradini, 1973, pl.21, fig.7, text-fig.6
Locus typicus: Mt. Aldone, Piacenza, Italy
Stratum typicum: Late Cretaceous-?Palaeocene
Original diagnosis: Corradini, 1973, p. 143
Chorate cyst with subspherical to ovoidal central body composed of thin, smooth endophragm and periphragm. Length of processes like or exceeding the diameter of the central body. Tubiform processes slightly constricted near their apex and expanded distally in aculeate margins.
Apical archeopyle tetratabular.
Dimensions--Holotype: diameter of the central body 32x34 µm, length of the processes 25-36 µm. Range: diameter of the central body 30-(37)-42 µm, length of the processes 20(30)38 µm, length of the distal spines 4-6 µm.
Original description: Corradini, 1973, p. 143
From the thin, smooth periphragm arise hollow, tubiform processes, one per plate area, slightly tapering distally. Distal margin terminating in a rosette of orthogonal short spines which are 5 to 8 in number. The processes on a specimen do not vary a great deal in their length or width. Sulcal processes not ptesent. Reflected tabulation 4", 6", 6""", 1p, 1"""".
Affinities:
Corradini, 1973, p. 143: The new species may be regarded as an intermediate species between O. buciniferum and O. complex. These chiefly differ in the distal structure of the processes. The first one is characterized by having an entire margin, the second by the numerous and complex appendages. Another intermediate species may be O. asterigerum (Gocht) but the distal spines of its processes are longer than by O. intermedium and occur around the processes more irregularly. Furthermore they are not so complex as shown by the appendages of O. complex. Slight differences occur also between the processes of O. complex and O. pulcherrimum. It is quite evident that just one character (shape of terminal spines) cannot be taken into account to differentiate so many species.
The study of my material clearly shows that transitional forms exist which may be erected to a specific level. Pending a revision on such group of forms, I prefer to follow the majority of the authors, who consider all these species as valid, also for the stratigraphical value they apparently have. O. prolixispinosum Davey & Williams is distinghuished from O. intermedium by a very elongated central body, thinner processes, and by having one or more sulcal processes. Taking into account the number of processes, it seems that some forms, previously related to other genera, belong to the new species. This is the case for some specimens reported by Valensi (1955) as Hystrichosphaeridium tubiferum and for that illustrated by Gorka (1963) as H. asterigerum. These forms, in fact, don"t have the high number of processes typical of Ilystrichosphaeridium, and lack the cingular ones.