Foramenal disposition

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Fig. 1. Endoskeletal patterns in discoidal shells. A-D: disposition of apertural axes. A: radial axes alternating in radial position from one stolon layer to the next. This is the most common disposition in imperforate forms with annular stages of growth. B: radial axes superposed in radial position on all stolon planes. C: crosswise-oblique stolon axes alternating in radial position from one stolon plane to the next. D: crosswise-oblique stolon axes superposed on all stolon planes. This pattern characterizes all members of the orbitolitid family. Schematic, not to scale. E-H: all endoskeletal elements are disposed in accordance with the basic patterns of the foraminal axes: E corresponds to pattern A, F to pattern B, G to pattern C and H to pattern D. Stereographs after Hottinger, 1967. Schematic, not to scale. In reality, the patterns are often disturbed by intercalary elements generated as the diameter of the annuli increases during growth. This maintains on the apertural face the mean distances between apertures and their mean diameter constant during ontogeny. Examples: E1-2: Pseudotaberina malabarica, megalospheric generation, from Iran. Middle Miocene. E1: oblique-centered section of spiral-involute stage showing radial disposition of pillars. Laterally, there is a layer of short septula. E2: a transverse section tangential to a septum shows the alternating disposition of the foramina and the pillars. F1-2: New genus (possibly related to Pastrikella) from the Pyrenean Upper Cretaceous in Northern Spain. The endoskeleton consists only of septula. There is but one median annular preseptal passage and it occupies the total radial extension of the annular chamber. There are only two planes of stolons. F1: an oblique section at a low angles with respect to the equatorial plane shows the radial disposition of the apertural axes and of the septula. F2: a transverse section parallel to the shell axis shows that the stolon axes on the two stolon planes are superposed. G1-3: Amphisorus from Rottnest Island near Perth, Australia. Recent. G1: the detail of an equatorial section demonstrates the crosswise-oblique disposition of the pillars on neighboring stolon planes. G2, an equatorial section, demonstrates that pillars are restricted to the equatorial zone of the disc. G3: a transverse section parallel to the shell axis and tangential to an annular septum shows the disposition of the median foramina and pillars altermating in radial position on successive stolon planes. They are flanked by two annular preseptal passages separating them from a lateral layer of septula subdividing the annular chamber. H1-2: Orbitolites spp. from the region of Tremp, Lerida prov., Northern Spain. Pyrenean Lower Eocene (Ilerdian). H1: the comparatively regular disposition of the ramps in sections parallel to the equatorial plane reveals their superposition in consecutive stolon planes. H2: in the transverse section parallel to the axis of the shell this superposition is clearly visible where the section is tangential to an annular septum. Abbreviations: b: beam; f: foramen; pi: pillar; prp: preseptal space; ra: ramp; s: septum; sl: septulum; (Hottinger, 2006; fig. 47)[1] CC/BY-NC-SA)
Fig. 2. Stolon planes and foramenal axes in discoidal-annular and conical-uniserial shells. Schematic, not to scale; A: Discoidal shell with a broadening periphery. Green and blue stolon planes are added step by step to the equatorial plane (E) as the shell margin thickens during ontogeny. The sector cut from the disc is cut in its turn in a transverse direction. B: A cone composed of a single series of discoidal chambers of which the marginal and axial areas are differentiated by colour. Note the distribution of the marginal area, the emplacement of the exoskeleton, and of the axial area housing the endoskeleton, in axial, horizontal (basal) and transverse sections. The axis of the shell is indicated by a vertical arrow. The surface of the cone is called the cone mantle, its horizontal termination is the cone base. A vertical line on the slanting surface of the cone is called a cone mantle line. The cone radius is indicated by a double arrow. C: The stolon axes are distributed on cone mantles in conical- uniserial foraminifera. If the cones increase their radial dimension markedly during growth, additional cone mantles are added in order to maintain the radial distances between the cone mantles relatively constant. This addition of cone mantles disturbes the regularity of the endoskeletal structures. In the models D-G, the addition of cone mantles during ontogeny is not taken into account. D-G: arrangement of stolon axes on cone mantles in the so-called radial zone of the cone is in accordance with the four basic patterns that govern discoidal structures. In conical shells, however, the stolon planes are replaced by cone mantles. As the cone increases in radius during growth, new stolon axes are intercalated in the cone mantles (arrows). D: stolon axes in the cone mantles alternate in radial position as a mantle is added, e.g. Dictyoconus. E: arrangement of stolon axes on cone mantle lines aligned on a cone radius. F: crosswise-oblique arrangement of stolon axes alternating in radial position on successive cone mantles. G: crosswise-oblique arrangement of stolon axes in line on a shell radius on subsequent cone mantles. This structure is a characteristic of Orbitolina; (Hottinger, 2006; fig. 80 [2] CC/BY-NC-SA)

Definition

  • according to Hottinger (2006):

FORAMENAL DISPOSITION - the pattern generated by a regular spacial disposition of foramina on septal faces.







See also


References

Hottinger (1967), Foraminifères imperforés du Mésozoïque marocain, Notes et Mémoires du Service géologique, Rabat, N° 209, p. 5-168

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

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