Fig. 1. Supplemental skeletons including marginal crests. A-G: Pellatispira group provalei Yabe. H: P. fulgeria Whipple. Both species from Kalimantan, Borneo, Indonesia. Middle-Upper Eocene. I-J: Calcarina sp., Kutei basin, Kalimantan. Pleistocene. A-D: SEM micrographs. G-J: transmitted light micrographs of oriented thin sections of free specimens. A: the free nepiont shows early spiral chambers not yet covered by a supplemental skeleton. An uncovered open interlocular space remains between the ultimate and penultimate chambers. B: detail of lateral view of a free nepiont revealing the early presence of canaliculate spines in the first volution of the spiral chambers and the modest extent of the marginal crest at this stage of growth. C: peripheral view of the margin of the second whorl. Note the strong radial spikes that support the thin imperforate walls of the marginal crest. D: septal face in oblique-peripheral view: the septal flap is reduced to a small area above the foramen. E: a lateral, flying cover of the interlocular space, with canal orifices at its margins, is produced by a free fold of an outer lamella and represents thus a primary element of the supplemental skeleton. F: in later growth stages, a first imperforate cover of the interlocular space may be bridged by supplementary chamberlets with a perforate, bilamellar wall. G: equatorial section. The primary bilamellar walls of the spiral chambers are coloured. All uncoloured constituents of the shell are part of the supplemental skeleton. H: Extreme development of the supplemental skeleton as a broad marginal crest covered with piles that are flanked by the canals of an enveloping system. I: the axial section of a trochospiral shell demonstrates the complex pattern of the umbilical cavities between umbilical piles of lamellae. The primary bilamellar walls of the spiral chambers are coloured. J: a section perpendicular to this axis of coiling shows that canalicular spines grow outward from the supplemental skeleton that envelops the primary bilamellar (coloured) wall of the spiral chambers. Abbreviations: a: aperture; c: canals, canal orifices; ch: (spiral) chamber; chl: (supplemental) chamberlet; csp: canaliculate (pseudo)spine; f: foramen; is: intraseptal interlocular space; lh: loophole; mcr: marginal crest; p: pore; pil: pile (of lamellae); pr: proloculus; s: septum; schl: supplemental chamberlet; sf: septal flap; sk: supplemental skeleton; spi: spike; uc: umbilical cavity system; up: umbilical plate; (Hottinger, 2006; fig. 65  CC/BY-NC-SA)
- according to Hottinger (2006):
SUPPLEMENTAL SKELETON - the imperforate refolds and flying covers produced by outer lamellae that cover and/or restrict interlocular spaces to form enveloping canal systems, canaliculate spines, marginal crests and marginal cords and the perforate chamberlets that are fed exclusively by canal orifices and that overgrow in more or less regular layers or tires the canalicular structures. The cavities of the supplemental skeleton can not be assigned to particular stages of growth because there is no direct connection with the orderly cameral system of shell cavities. In shells with an extensive supplementary skeleton, the cameral cavity system is reduced to neanic or even nepionic stages.
Remarks: Introduced by Carpenter (1862) long before lamellar theory was developed, and as now refined here, the term is a welcome complement to the terms exoskeleton and endoskeleton. Both of these terms subdivide the chamber lumen while "supplemental skeleton" structurizes extralocular, "outer" space. It is meant to be used as generic term regrouping all forms that have canaliferous enveloping, marginal and pseudospinose structures like Siderolites, Pellatispira, Calcarina and their allies along with all types of marginal cords (linked to a single sulcus) as in Sulcoperculina and their derivatives, Ranikothalia and all nummulitids s.str.
Carpenter, Parker & Jones, (1862). Introduction to the study of Foraminifera. Ray Society, London, 319 p. + 22 pls.
Hottinger (2006), Illustrated glossary of terms used in foraminiferal research. Carnets de Géologie, Memoir 2, ISSN 1634-0744
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