Fig. 1. The folium and its apertures. All specimens from the Gulf of Aqaba, Red Sea, Recent. SEM graphs. A-D: Rosalina bradyi (Cushman); A: detail of dissected specimen, oblique-ventral view. The approximate position of the breakage surface (arrows A-A) is indicated by the line A-A in Fig. B. B: ventral view showing the folium at its maximum development, with anterior and posterior apertures. C-D: peripheral and dorsal views. Note the restriction of the perforation to the dorsal surface of the shell, an indication that the face extends from the umbilical side of the shell over its periphery. E-H: Asterorotalia gaimardi (d'Orbigny). E-F: dissected specimens showing details of advanced umbilical architecture covered by the folia: foraminal and coverplates. G: oblique-ventral view showing the folia that cover the ventral part of the interlocular space. H: dorsal view showing the spiral arrangement of the chambers. a: aperture; ch: chamber lumen; cp: cover plate; f: foramen; fo: folium; foa: foliar aperture; fochl: foliar chamberlet lumen; fp: foraminal plate; is: interlocular space; li: lip (of foramen); n: notch; sf: septal flap; u: umbilicus; (Hottinger, 2006; fig. 53) 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):
SEPTAL FLAP - (paries proximus, pars auct.); that part of the inner lamella that covers the preceding septal face. By its adherence to the septal face, the septal flap produces a trilamellar septum in a primarily bilamellar foraminifer. It may extend into an umbilical plate, a foramenal plate, a bipartitor, a cover plate or a toothplate (Fig. 1F; Fig. 2I-J).
Remarks: The term septal flap was used earlier for all parts of the proximal chamber wall, Lévy's paries proximus (Lévy et alii, 1979). Here we restrict it to those areas of the proximal chamber wall that are glued to the face of the previous frontal chamber wall. This area may be minimized to a narrow hemicircular band around an interiomarginal foramen or reduced to sectors extending from the foramen over the face of the previous chamber either in equatorial or in dorsal direction. Free parts of the proximal chamber wall are covered by outer lamellas like all free outer surfaces of the lamellar shell. The open space between frontal and proximal walls of subsequent chambers is called intraseptal interlocular space. The line of adherence of the septal flap on the previous frontal chamber wall delimits the intraseptal interlocular space in proximal direction and is in fact a deeply sunken cameral suture.
Lévy, Mathieu, Poignant, Rosset-Moulinier & Rouvillois, (1979), Révision de quelques genres de la famille Discorbidae (Foraminiferida) fondée sur l'observation de leur architecture interne, Revue de Micropaléontologie, Paris, vol. 32, N° 2, p. 66-88.
Hottinger (2006), Illustrated glossary of terms used in foraminiferal research. Carnets de Géologie, Memoir 2, ISSN 1634-0744
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