Elongation index

From Foraminifera
Revision as of 14:31, 15 April 2019 by Aspadlo (talk | contribs)
(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)
Jump to: navigation, search
Fig. 1. Regeneration in fusiform-elongate shells: A-D: Alveolina gigantea Checchia-Rispoli. Microspheric generation. Palermo, Sicily, Middle Eocene. E: Pseudoschwagerina sp., megalospheric specimen, from Palazzo Adriano, Sicily, Permian. A: a fragment of the polar realm of the shell cut in the axial direction shows two periods of regeneration (red lines designated by arrows) during late ontogeny. B: a similar fragment cut in a direction perpendicular to the shell axis, with one broken surface, that has been regenerated in an attempt to restore the cylindrical shape of the shell. At such a late ontogenetic stage the original shape of the shell can not be regained through regenerative growth. Incident light micrographs. C-D: regeneration at an early stage of ontogeny: C. the rate of elongation was higher in the regenerated half of the shell (red curve) than in the undisturbed half, until the range of elongation that is characteristic for the species was attained again. Note the absence of elongation index increase in the early whorls broken away (arrow). Data from Hottinger, 1962. D. Compare the camera lucida drawing of an axial section: broken early shell in gray, regenerated shell in black. E: in a fusulinid the regeneration of the broken whorls 3-6 produces an almost perfect equatorial spiral after only two more whorls of growth; (Hottinger, 2006; fig. 78 [1] CC/BY-NC-SA)

Definition

  • according to Hottinger (2006):

ELONGATION INDEX - in alveolinids and other fusiform or otherwise elongate shells, the ratio of the length of the axis of coiling to the diameter at the equator.


References

Hottinger (1962), Recherches sur les Alvéolines du Paléocène et de l'Éocène, Schweizerische Paläontologische Abhandlungen, Basel, N° 75/76, 243 p. + 18 pls.

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

                          | Foraminifera  |  FORAM-Links | Contributors |