Pore

From Foraminifera
Jump to: navigation, search
Fig. 1. The pore and its organic constituents; A: a pore in an inner chamber covered by an outer whorl, according to Leutenegger (1977), schematic, not to scale. B: Accumulation of mitochondria below a pore mouth in Bolivina sp., thus indicating the pores' main function: gas exchange. TEM micrograph of a section oblique to the surface ot the wall that exaggerates the thickness of the pore discs. The detachment of the outer lamella 2 (ouL 2) is an artifact of preparation. x 24,000. Courtesy S. Reber-Leutenegger. C: Resin cast of pores in the lateral chamber wall of Nummulites partschi De La Harpe with trabeculae. The carbonates of the shell are dissolved with HCl. SEM graph x 1,000. D: Outer pore mouths in the lateral suface of chamber wall of Assilina. Note the annular attachment of the interlamellar discs. SEM graph x 5,000. E: Inner pore mouths in the lateral chamber wall of Assilina shaped as eggholders (in order to keep the symbionts below their breathing chimneys). Note the annular suture of the pore plug. SEM graph x 5,000. C-E: from Hottinger, 1977. F: Perforation pattern on the dorsal surface of Challengerella persica (Recent, Persian Gulf): densely perforated porefields between imperforate ornamentation. SEM: oblique dorsal view of shell, x 30, and detail of porefield, x 500. G: Perforation pattern in Ammonia reyi Marie (Pliocene, Dar bel Hamri, Northern Morocco): densely perforated porefields between loosely perforated ornaments. SEM graphs of dorsal shell view (x 30) with detail (x 500). F-G: from Billman et alii, 1980; Abbreviations: bD: basal (pore) disc; Cy: cytoplasm; iL: inner lamella; ilD: interlamellar disc; iol: interlamellar organic lining; ls: lacunar system (in the cytoplasm); M: mitochondria; ML: median layer separating inner from outer lamellas; OL: Organic lining (here difficult to separate from plasmalemma of host); ouL 1: primary outer lamella; ouL 2, ouL3: subsequent outer lamellas; P: pore; Pc: organic pore coat; Pl: plasmalemma; ppl: pore plug (note its porosity); Spl: (biomineralized) sieveplate; V: vacuole; (Hottinger, 2006; fig. 75)[1] CC/BY-NC-SA)


Definition

  • according to Hottinger (2006):

PORE is a minute tubular perforation traversing a lamellar chamber wall, coated internally by an organic sheathe. Subdivided by organic discs ("pore plate" auct.) and closed off internally by the inner organic lining. The latter may fuse with the basal disc corresponding to the median layer and form an organic pore plug. The size and shape of the external and internal pore openings may be identical (rounded to elongated) or dissimilar, when symbionts are positioned in egg-holders below the pore mouths for gas exchange. Ultrathinsections of living benthic foraminifera that show in the TEM some cytoplasm in pores are considered to be artefacts due to imperfect preparation. Compare: parapores; pits.


See also


References

Billman, Hottinger & Oesterle (1980), Neogene to Recent Rotaliid Foraminifera from the Indopacific Ocean; their canal system, their classification and their stratigraphic use, Schweizerische Paläontologische Abhandlungen, Basel, N° 101, p. 71-113.

Hottinger (1997), Shallow benthic foraminiferal assemblages as signals for depth of their deposition and their limitations, Bulletin de la Société géologique de France, Paris, vol. 168, N° 4, p. 491-505.

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

Leutenegger (1977), Ultrastructure de Foraminifères perforés et imperforés ainsi que de leur symbiotes, Cahiers de Micropaléontologie, Paris, fasc. 3-1977, 52 p. + 54 pls.


                      | Foraminifera  |  FORAM-Links | Contributors |