Marginal canal system

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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: loop-hole; 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 [1] CC/BY-NC-SA)


Definition

  • according to Hottinger (2006):

MARGINAL CANAL SYSTEM - enveloping canals grouped at the periphery of the shell, often extended in radial direction, as in Pseudosiderolites, in contrast to cords, where the peripheral orientation of the canals is emphasized.


Remarks: Hottinger (1978) used this term as a synonym of marginal cord. It seems preferable now to distinguish between predominantly radial and peripheral systems. The latter are never modified to include canaliculate spines.



See also



References

Hottinger (1978), Comparative anatomy of elementary shell structures in selected larger Foraminifera. In: Hedley R.H. & Adams C.G. (eds.), Foraminifera, Volume 3, Academic Press, London, p. 203-266.

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

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