Back
Operculodinium severinii
Operculodinium severinii (Cookson and Cranwell, 1967) Islam, 1983
Originally Baltisphaeridium, subsequently Impletosphaeridium, thirdly (and now) Operculodinium.
Holotype: Cookson and Cranwell, 1967, pl.3, fig.1
Locus typicus:
Stratum typicum: Eocene-Oligocene
Original description (Cookson & Cranwell, 1967):
Baltisphaeridium severinii Cookson & Cranwell, new speices (Pl. 3, figs. 1-2)
Description: Shell relatively large, approximately circular to ellipsoidal in outline, covered with densely arranged, tapering, unbranched processes which gradually decrease I width from broad t, somewhat conical bases to over half their length, and then narrow rapidly to end I fine, frequently curved, very sender, apparently closed apices. Wall thin, usually obscured by the processes.
Dimensipons of the Leña Dura material: Holotype – overall diameter ca. 99 µm, shell diameter ca. 76 µm, wall, thickness ca. 2 µm, processes mainly 10-16 µm long. Range in size of 20 speicemns: overall diameter ca. 75-114 µm, shell diameter ca. 55-85 µm, length of processes 10-25 µm.
Age and occurance: Lower tertiary, Lenña dura Formation near Punta Arenas, Chile.
Olotype: Plate 3, fig. 1; slide JSB-56:20 – single mount (Wild M20 99.5/36), at present I collections of L. M. Cranwell.
Comments: B. severinii appears to be closely related to B. whitei (Deflandre and Courville, 1939), a Senonian species first described from French flints at Marong, and to B. nanum Cookson (1965a) from Upper Eocene deposits from Browns Creek, southwest Victoria. It differs from both species, however, in 1) the larger size of the shell which. Which is 60-85 µm as compared with 23-34 µm in B. nanum and 56-60 µm in B. whitei, and in 2) the size and shape of the processes , particularly in respect to their broad-based appearance. Furthermore, the small opening occasionally seen in B.nanum has not been found in B. severinii.
Katz (1961) has reported redeposited B. pilosum (Ehrenberg) from the Agua Fresca Formation in Chile, which is of Eocene age, but this species has not been seen by us in the Leña Dura preparations.
Emended diagnosis: Islam, 1983, p. 342:
Cyst subspherical to ellipsoidal, proximochorate to skolochorate and biphragmal; periphragm chagrinate, granulate or reticulate; numerous nontabular solid processes proximally conical, tapering to mid-length and continuing as thin slender forms to acuminate tips; processes sometimes flexible; archeopyle precingular type P but frequently indistinguishable.
Remarks. The present generic reallocation and emendation of the diagnosis of the species comes about because of the presence of a precingular type P archeopyle in some specimens. It differs from other species of the genus in process morphology by which it resembles Eocladopyxis Morgenroth 1966 which possesses an epicystal archeopyle. Liengjarern et al. (1980) mentioned the possible presence of such archeopyle sutures and hence projected the possibility of a "retransfer" to Eocladopyxis. However, in the present study and also in Goodman (1979), the precingular archeopyle of the species is quite clearly shown (pl. 4, fig. 1 shows some mechanical damage).
Originally Baltisphaeridium, subsequently Impletosphaeridium, thirdly (and now) Operculodinium.
Holotype: Cookson and Cranwell, 1967, pl.3, fig.1
Locus typicus:
Stratum typicum: Eocene-Oligocene
Original description (Cookson & Cranwell, 1967):
Baltisphaeridium severinii Cookson & Cranwell, new speices (Pl. 3, figs. 1-2)
Description: Shell relatively large, approximately circular to ellipsoidal in outline, covered with densely arranged, tapering, unbranched processes which gradually decrease I width from broad t, somewhat conical bases to over half their length, and then narrow rapidly to end I fine, frequently curved, very sender, apparently closed apices. Wall thin, usually obscured by the processes.
Dimensipons of the Leña Dura material: Holotype – overall diameter ca. 99 µm, shell diameter ca. 76 µm, wall, thickness ca. 2 µm, processes mainly 10-16 µm long. Range in size of 20 speicemns: overall diameter ca. 75-114 µm, shell diameter ca. 55-85 µm, length of processes 10-25 µm.
Age and occurance: Lower tertiary, Lenña dura Formation near Punta Arenas, Chile.
Olotype: Plate 3, fig. 1; slide JSB-56:20 – single mount (Wild M20 99.5/36), at present I collections of L. M. Cranwell.
Comments: B. severinii appears to be closely related to B. whitei (Deflandre and Courville, 1939), a Senonian species first described from French flints at Marong, and to B. nanum Cookson (1965a) from Upper Eocene deposits from Browns Creek, southwest Victoria. It differs from both species, however, in 1) the larger size of the shell which. Which is 60-85 µm as compared with 23-34 µm in B. nanum and 56-60 µm in B. whitei, and in 2) the size and shape of the processes , particularly in respect to their broad-based appearance. Furthermore, the small opening occasionally seen in B.nanum has not been found in B. severinii.
Katz (1961) has reported redeposited B. pilosum (Ehrenberg) from the Agua Fresca Formation in Chile, which is of Eocene age, but this species has not been seen by us in the Leña Dura preparations.
Emended diagnosis: Islam, 1983, p. 342:
Cyst subspherical to ellipsoidal, proximochorate to skolochorate and biphragmal; periphragm chagrinate, granulate or reticulate; numerous nontabular solid processes proximally conical, tapering to mid-length and continuing as thin slender forms to acuminate tips; processes sometimes flexible; archeopyle precingular type P but frequently indistinguishable.
Remarks. The present generic reallocation and emendation of the diagnosis of the species comes about because of the presence of a precingular type P archeopyle in some specimens. It differs from other species of the genus in process morphology by which it resembles Eocladopyxis Morgenroth 1966 which possesses an epicystal archeopyle. Liengjarern et al. (1980) mentioned the possible presence of such archeopyle sutures and hence projected the possibility of a "retransfer" to Eocladopyxis. However, in the present study and also in Goodman (1979), the precingular archeopyle of the species is quite clearly shown (pl. 4, fig. 1 shows some mechanical damage).