Revision as of 14:53, 10 May 2019
Fig. 1. Marginal cord in nummulitids. A-B: Assilina ammonoides (Gronovius), Recent, Gulf of Aqaba, Red Sea. SEM graphs after Hottinger, 1977. A: Detail of marginal cord in a shell broken in the axial plane. Double arrow B - B indicates the approximate position of the cut in the cast of Fig. B. B: Detail of marginal cord in an epoxy resin cast that was cut approximately in the equatorial plane (as indicated in Fig. A), showing canal and chamber lumina after dissolution of shell. White arrows indicate direction of growth. C: Nummulitic limestone from Steinbach, Einsiedeln, Swiss Helvetic Alps, Lower Eocene (Cuisian). Transparent light micrograph of section perpendicular to bedding plane. 1: Assilina sp. of A. ammonea- praespira phyletic line, with particularly large and prominent marginal cord; 2: Nummulites spp.; 3: Assilina sp. of A. spira phyletic line; 4: Assilina sp. of A. exponens phyletic line; 5: Asterigerina cf. rotula (Kaufmann): no marginal cord; ch: chamber lumen; isc: intraseptal canal system; mc: marginal cord; mcc: marginal cord canals; sf: septal flap; st: stolon; sulc:sulcus canal; (Hottinger, 2006; fig. 64  CC/BY-NC-SA)
Fig. 2. Alar prolongations and involuteness in lamellar foraminifers; A-B: Involuteness and evoluteness in lamellar foraminifers: an accurate definition is whether or not perforate walls (double arrow) cover the next whorl. Axial section, schematic, not to scale. Note the numerous, outer lamellas (green) enveloping the total exposed surface of the previous shell (compare "lamellation"). The distribution of the inner lamella (red) covering the previous whorl hasno significance in the definition of involuteness. Red: lumen of alar prolongation, yellow: lumen of equatorial chamber. alp: alar prolongation; il: inner lamella; mc: marginal cord; ol: (numerous) outer lamellas; p: pore; sulc: sulcus; (Hottinger, 2006; fig. 7  CC/BY-NC-SA)
- according to Hottinger (2006):
SULCUS - a peripheral infold of primary chamber-wall, always imperforate. May or may not have radial passages between the underlying chamber-lumen and the ambient environment or the interlocular space. May or may not be covered by additional marginal structures, such as a marginal cord.
Remarks: Revets (1989, 1993) uses the term sulcus for the adapertural depression between the apertural rim and the attached part of the toothplate. This depression is positioned near or in the axis, not at the periphery of the spiral shell, and should therefore be distinguished from the nummulitid sulcus by a separate term, the "adapertural depression".
Hottinger (1977), Foraminifères operculiniformes, Mémoires du Muséum National d'Histoire Naturelle, Paris, (Série C, Sciences de la terre), t. XL, 159 p. + 66 pls.
Hottinger (2006), Illustrated glossary of terms used in foraminiferal research. Carnets de Géologie, Memoir 2, ISSN 1634-0744
Revets (1989), Structure and comparative anatomy of the toothplate in the Buliminacea (Foraminiferida), Journal of Micropaleontology, London, vol. 8, part 1, p. 23-36.
Revets (1993), The foraminiferal toothplate, a review, Journal of Micropaleontology, London, vol. 12, part 2, p. 155-168.
| Foraminifera | FORAM-Links | Contributors