Counterseptum

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Fig. 1. Countersepta. A-D: Amphistegina tuberculata Bermudez, Dominican Republic, Upper Miocene, SEM stereographs showing the split halves of a megalospheric shell. A: dorsal side in ventral view, B: ventral side in dorsal view, with details in C and D. E-G: Amphistegina lopeztrigoi Palmer, thin slides in transmitted light micrographs, Eocene, Florida. Generic and specific name are unclear and need revision. E: centered section perpendicular to the coiling axis; F: section perpendicular to the coiling axis located below the megalosphere; G: poorly centered axial section. cs: counterseptum; egh: eggholder; f: main foramen; pust: pustules covering successive faces; s: septum of main chambers; stc: stellar chamberlet; (Hottinger, 2006; fig. 33 [1] CC/BY-NC-SA)

Definition

  • according to Hottinger (2006):

COUNTERSEPTUM - a kind of lower lip of an interiomarginal - basal aperture appearing in appropriate sections as a forward directed hook below the foramen and glued to the previous shell whorl, as in Eulinderina guayabalensis (Nuttall) or Amphistegina lopeztrigoi Palmer (Butterlin, 1987). The hook is said to develop into "complete septal walls" in Helicostegina.


Remarks: The term was introduced by Barker and Grimsdale (1936) for proximal portions of the main chamber septum below the main foramen in A. lopeztrigoi. The hook may be identical with the gutter in Old World amphisteginids. The nature of the "complete", helicosteginid countersepta remains to be analysed the more so as the relation between "countersepta" and stellar septula in the New World amphisteginids is not clear.

References

Hottinger (2006), Illustrated glossary of terms used in foraminiferal research. Carnets de Géologie, Memoir 2, ISSN 1634-0744

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