Cassidulinidae (Foraminiferida) from the Uppermost Cenozoic of Japan (Part 1)
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概要
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The family Cassidulinidae from late Cenozoic sediments of Japan is examined by means of optical and electron microscopes. Among the total of 76 taxa including species and subspecies, 24 species and 2 subspecies are described as new. Three new genera Takayanagia, Paracassidulina and Hastilina are also proposed. For the taxonomic classification, various external and internal characters including wall microstructure, internal structure, aperture, perforation, and test ornamentation are re-evaluated with particular emphasis placed on problems concerning the formation and function of these features. In considering these features, family Islandiellidae Loeblich and Tappan belonging to the superfamily Buliminacea is abandoned. Many genera which have been included in that family are now transferred to the family Cassidulinidae. The test walls of the Cassidulinidae are composed of three calcitic structural components, outer veneer, crystalline structure, and inner veneer. Four major types of pores are recognized; the shape of pores on the external test surface is regulated by the outer veneer and successive growth lamellae. External and internal apertural modifications such as toothplate, lip, and plate are examined in detail, which necessitated the redefinition of their structural features. Nine basic apertural forms are recognized, which are important to the determination of generic relationship. Based on the differences in structure of crystal units, four types of basic test structure can be recognized in the optically radial and granular textures. These are fibrous crystalline structure, bundle-shaped crystalline structure, intricate crystalline structure, and clumpy crystalline structure. The first two types correspond to the distinctly radial and indistinctly radial textures, respectively, and the remaining two to the optically jagged-granular and mosaic-granular textures. The main factors which cause these types involve undoubtedly genetical and possibly environmental effects. A slight difference in the shape of crystal units is ascribed to specific difference and dramatic difference in radial-granular texture is considered as generic importance. These ultrastructures seem to have resulted from intrinsically similar calcification processes; the fundamental structure of crystal elements is similar to each other, but the difference exists in their inclination. This observation indicates that the radial-granular texture has no taxonomic significance in the suprageneric classification.
- 東北大学の論文
- 1983-02-25
著者
関連論文
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- Cassidulinidae (Foraminiferida) from the Uppermost Cenozoic of Japan (Part 2)
- Cassidulinidae (Foraminiferida) from the Uppermost Cenozoic of Japan (Part 1)