@article{oai:tohoku.repo.nii.ac.jp:00012002,
 author = {Takayanagi, Yokichi and Niitsuma, Nobuaki and Sakai, Toyosaburo},
 issue = {2},
 journal = {The science reports of the Tohoku University. Second series, Geology  = 東北大学理科報告. 地質学},
 month = {Nov},
 note = {application/pdf, Current studies on planktonic Foraminifera indicate that the external morphology of the test and the structure of the wall are of prime importance for taxonomy, ecology and studies on their evolution. Investigations on the spatial variation of the morphology and on the microstructure of the shell wall provides sound basis for the evaluation of the chronologic morphogenesis of the planktonic Foraminifera. In the present study the well known planktonic species, Globorotalia truncalulinoides (d'Orbigny), was analysed as to the geographic variation of its external morphology, and the wall structure was examined with the electron microscopes. Statistical analyses demonstrate that : 1) highly conical forms are seemingly concentrated in the lower latitudinal regions and the lower conical ones in the higher latitudes; 2) individuals with umbilical teeth and dextrally coiled shells dominate in the lower latitudes; the categories are independent of one another. Two methods of electron microscopy were employed for the study of the wall microstructure, namely, the transmitted type and the scanning type. A complete electron micrograph of a vertical section of the test was reconstructed, and a schematic diagram showing the fundamental wall structure constructed. The wall of G. truncatulinoides is basically divided into the lamellar layer and crust; these are different from each other in microstructure. The lamellar layer in each chamber is distinguished into the inner and outer lamellae by structure and texture. The inner lamella, limited in each chamber, consists of minute interlocking calcite grains and is lined by basal sublamella. The outer lamella is composed of interlocking columns and wedges perpendicular to the surface and finely bumpy in texture. The boundary between these lamellae is not defined by a sharp line or "canal" in contrast to those between the consecutive outer lamellae. Textural differentiation in the bilamellar layer is considered to be related to the contact with the protoplasmic mass. The crust composed of elongate, prismatic calcite units is a layer formed after the completion of the ultimate chamber. These calcite units exhibit a microstructure supposed to be cleavage. Pore concentration in the wall is usually 7 to 9 per 25×25μ square. Protuberances developed in and on the wall are classified into punctae and pustules on the basis of site of occurrence, structure, and external morphology. Keels, umbilical teeth, and inner margins of the umbilical walls are essentially identical in structure with the usual type of the wall, though each of them assumes a peculiar feature in some respects. The characteristic features of the keel are mostly due to the thickening of the basal suite of the lamellae formed by an inflection at the periphery., 紀要類(bulletin), 14031646 bytes},
 pages = {141--A27},
 title = {Wall Microstructure of Globorotalia truncatulinoides (d'Orbigny)},
 volume = {40},
 year = {1968}
}