Fig. 1. Comparison of foraminiferal skeletons. Schematic, not to scale. Lamellation, perforation and canal orifices omitted. A: a planispiral-evolute shell without skeletal structures, composed of simple primary chamber walls with multiple apertures, such as that of Peneroplis. B: a planispiral-evolute shell with an alveolar exoskeleton, such as Pseudocyclammina. C: a planispiral shell with a pillared endoskeleton such as Archaias. Note that in the axial sections of shells with peneropliform, flaring chambers the periphery of the shell and the apertural face are on opposite sides. Consequently, the pillars extending from chamber bottom to chamber roof appear in the axial plane on the side cutting the apertural face as longitudinal and on the other side cutting the periphery as more or less perpendicular sections. D: a spiral shell with a supplemental skeleton restricted to the periphery of the shell, as in nummulitids with a marginal cord. E: a spiral shell with an enveloping canal system and a marginal crest as in Pellatispira. Note the primary lateral chamber walls "emerging" from the supplemental skeleton. These primary chamber walls are covered by secondary lamellae but are perforated in continuation of the primary bilamellar wall. Therefore they are not a part of the supplemental skeleton. The supplemental chamberlets have perforate lateral walls but do not communicate directly with the spiral chambers by retral stolons. They are fed by canal orifices. a: aperture; af: apertural face; alv: alveole; bl: basal layer; ch: chamber; chsut: chamber suture; f: foramen; lh: loophole; mc: marginal cord; mcr: marginal crest; per: periphery; pi: pillar; pr: proloculus; s: septum; schl: supplemental chamberlet; spc: spiral canal; spsut: spiral suture; sulc: sulcus; t: tunnel; up: umbilical plate; (Hottinger, 2006; fig. 63) CC/BY-NC-SA)
Fig. 2. 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):
SUPPLEMENTARY CHAMBERLET - a cavity in the supplementary skeleton that is bounded by a bilamellar, perforate wall in the direction of the ambient environment of the shell when it forms. It may be overgrown in later ontogenetic stages by subsequent outer lamellas or by additional elements of the supplementary skeleton.
Hottinger (2006), Illustrated glossary of terms used in foraminiferal research. Carnets de Géologie, Memoir 2, ISSN 1634-0744
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