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)
- according to Hottinger (2006):
FOLIUM - (lip; tenon; umbilical flap; astral lobe, pars auct.); in spiral lamellar foraminifera an axial-umbilical portion of the lateral chamber wall, generally triangular in outline and often texturally differentiated (porosity). The limit between the main lateral chamber wall and the folium may be marked by a short, posterior indentation or "notch" and/or by an umbilical plate-suture. An opening (foliar aperture) is always present between the anterior margin of a folium and the adjacent previous coil. In addition, umbilical and/or posterior openings may be present, depending upon whether the folia are free or attached by their tips or along their posterior margin. In some genera such as Asterorotalia, the folia may extend onto the preceding chamber and be attached to it, partially covering intraseptal interlocular spaces wherever present. A folium is composed of the same layers as those forming the wall of the main chamber.
Hottinger (2006), Illustrated glossary of terms used in foraminiferal research. Carnets de Géologie, Memoir 2, ISSN 1634-0744
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