Sphaeroidinella dehiscens dehiscens immatura Cushman 1919 from: Quilty, P.G.. (1976): Planctonic foraminifera DSDP Leg 34- Nazca Plata . DSDP initial reports Vol. 34 | . |
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Forma Sphaeroidinella dehiscens dehiscens immatura Cushman 1919 |
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| Discussion / Comments: |
Quilty (1976):
Remarks: Morphotypes identifiable as this form were recorded onboard ship from Sample 319-1, CC. This identification now seems invalid although the age assigned is still correct. It now seems probable that the 5". d. d. immatura morphotypes in this fauna are dissolution artifacts formed by preferential dissolution at the triple chamber junction on the dorsal side of specimens of
Sphaeroidinellopsis subdehiscens paenedehiscens, leading to a synthetic dorsal sutural supplementary aperture.
Brönnimann and Resig (1969) suggested that to identify S. d. d. immatura, the specimen should have an obvious elevated border to this aperture. This is an excellent criterion to use where there is doubt concerning the identification of the dorsal sutural supplementary aperture,
for example, in the case cited here. In many circumstances, for example, in shallower water sediments, the difference between Sphaeroidinella and Sphaeroidinellopsis, is distinct and the evolution of Sphaeroidinella can be taken as "instantaneous" (Brönnimann and Resig, 1969, p. 1237).
Sphaeroidinella dehiscens dehiscens forma immatura is thus not recorded in this work. |
| Synonym list: |
Quilty (1976):
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| References: |
Cushman,J.A. (1919):
Fossil foraminifera from the West Indies . Carnegie Institute, Washington Publ. Vol. 291 p. 21-71
Quilty,P.G.. (1976):
Planctonic foraminifera DSDP Leg 34- Nazca Plata . DSDP initial reports Vol. 34
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