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Oligosphaeridium tubulatum
Oligosphaeridium ?tubulatum (Menéndez, 1965, p.13, pl.2, fig.7; pl.3, fig.17) Sarjeant and Stancliffe, 1994, p.56. Holotype: Menéndez, 1965, pl.2, fig.7.
Originally Micrhystridium (Appendix A), subsequently (and now) Oligosphaeridium?. Questionable assignment: Sarjeant and Stancliffe (1994, p.56); and Fauconnier and Cornu in Fauconnier and Masure (2004, p.404) as a problematic species.
Age: Oligocene.
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Original description: [Menéndez, 1965] (translated from Spanish):
Micrhystridium tubulatum
(Plate II, fig. 7, and Plate III, fig. 17)
DIAGNOSIS. Central body ellipsoidal, with smooth membrane; appendages arranged radially, widened at the base and at the apex, forming flattened, wide funnels with irregular margins; the membrane of the same is longitudinally striated.
HOLOTYPE. Prep. 1121(1) BA PB coord. 19.6-93, microse. Watson 90.128.
DIMENSIONS. Total diameter, 24.5 by 29.5 μ; central body, 13 by 18 μ; membrane thickness, 0.4 μ; length of appendages, 6.5 to 8 μ, and 1 to 2.5 μ wide.
DISTRIBUTION. 1121 m depth.
DESCRIPTION. - The holotype presents an elliptical central body measuring 13 by 18 μ, with a smooth membrane 0.4 μ thick; it has around 20 appendages, radially arranged, 6.5 to 8 μ long and 1 to 2.5 μ wide; these gradually become narrower toward their insertion point, but more noticeably toward the apex or free end, forming a wide, flat funnel with an irregular, somewhat frayed margin. The wall of the appendages is longitudinally striated.
Other specimens found at the same level do not provide further details, as their state of preservation is poor; it could only be added that some of them have thinner appendages.
COMPARISONS. - There is quite a similarity between this specimen from Tierra del Fuego and those from the Eocene and Oligocene of Australia determined by Cookson and Deflandre as M. cf ambiguum Defl. (Deflandre and Cookson, 1955: p. 281; plate 8, fig. 2, and Cookson, 1953: p. 116, plate 2, fig. 33), although they do not exactly agree, since the central body is granular, the ends of the appendages are not as expanded, and their width is narrower.
The edges of the appendages are very close to each other, and in some cases they appear to connect; but this is only a matter of overlapping. If such a possible connection existed, this species should be placed in the genus Cannosphaeropsis. Since the existence of such a connection cannot be confirmed in any of the observed specimens, I prefer to provisionally place the species in Micrhystridium.
Cannosphaeropsis urnaformis Cookson (1953: p. 118, plate II, fig. 42), from the Oligocene of Australia, has a general appearance similar to M. tubulatum; but it differs, first of all, in the generic character, not observed in the Tierra del Fuego specimen, of presenting connections between the appendages, in its larger size, and in having proportionally shorter and wider perforated appendages.
Originally Micrhystridium (Appendix A), subsequently (and now) Oligosphaeridium?. Questionable assignment: Sarjeant and Stancliffe (1994, p.56); and Fauconnier and Cornu in Fauconnier and Masure (2004, p.404) as a problematic species.
Age: Oligocene.
--------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Menéndez, 1965] (translated from Spanish):
Micrhystridium tubulatum
(Plate II, fig. 7, and Plate III, fig. 17)
DIAGNOSIS. Central body ellipsoidal, with smooth membrane; appendages arranged radially, widened at the base and at the apex, forming flattened, wide funnels with irregular margins; the membrane of the same is longitudinally striated.
HOLOTYPE. Prep. 1121(1) BA PB coord. 19.6-93, microse. Watson 90.128.
DIMENSIONS. Total diameter, 24.5 by 29.5 μ; central body, 13 by 18 μ; membrane thickness, 0.4 μ; length of appendages, 6.5 to 8 μ, and 1 to 2.5 μ wide.
DISTRIBUTION. 1121 m depth.
DESCRIPTION. - The holotype presents an elliptical central body measuring 13 by 18 μ, with a smooth membrane 0.4 μ thick; it has around 20 appendages, radially arranged, 6.5 to 8 μ long and 1 to 2.5 μ wide; these gradually become narrower toward their insertion point, but more noticeably toward the apex or free end, forming a wide, flat funnel with an irregular, somewhat frayed margin. The wall of the appendages is longitudinally striated.
Other specimens found at the same level do not provide further details, as their state of preservation is poor; it could only be added that some of them have thinner appendages.
COMPARISONS. - There is quite a similarity between this specimen from Tierra del Fuego and those from the Eocene and Oligocene of Australia determined by Cookson and Deflandre as M. cf ambiguum Defl. (Deflandre and Cookson, 1955: p. 281; plate 8, fig. 2, and Cookson, 1953: p. 116, plate 2, fig. 33), although they do not exactly agree, since the central body is granular, the ends of the appendages are not as expanded, and their width is narrower.
The edges of the appendages are very close to each other, and in some cases they appear to connect; but this is only a matter of overlapping. If such a possible connection existed, this species should be placed in the genus Cannosphaeropsis. Since the existence of such a connection cannot be confirmed in any of the observed specimens, I prefer to provisionally place the species in Micrhystridium.
Cannosphaeropsis urnaformis Cookson (1953: p. 118, plate II, fig. 42), from the Oligocene of Australia, has a general appearance similar to M. tubulatum; but it differs, first of all, in the generic character, not observed in the Tierra del Fuego specimen, of presenting connections between the appendages, in its larger size, and in having proportionally shorter and wider perforated appendages.