Morphostructure and systematics of Linderina brugesi Schlumberger, 1893 (Foraminifera, Eocene)

Abstract

Abstract The morphostructure of the genus Linderina Schlumberger , 1893 is revised relying on a structural studyof the type species L. bruguesi, Schlumberger . Its test is lamellar-involute, with annular-cyclic growth of ornitoidal type. It has only one kind of stolons which are crosswise-oblique, alternately arranged in axial rows, and correspond with the apertures in the last chamber. The lateral thickenings of the test are formed by the superposition of the successive involute outer lamellae of the different chambers, lacking piles and granules, and the irregularity of the lateral surfaces is due to the lateral rounded reliefs of the alternate chamberlets. The embryonic apparatus is quadrilocular, with three subspherical initial chambers forming a triconch, and a fourth larger, arcuate chamber with rows of apertures in both sides from which the orbitoidal growth starts. An explanation is given for the morphogenesis of embryos in triconch, observed in a number of foraminiferal genera. L. brugesi shows a close similarity to American Eocene species Caudriella ospinae ( Caudri ), which differs from Linderina in that it has lateral chamberlets. Because of this affinity, Caudriella is included in the Linderinidae. A redefinition of the genus Linderina and of the family Linderinidae is performed. The genera Eoannularia and Epiannularia, previously classified into the Linderinidae, do not fit into the new characterization of the family and are thus grouped into a new family, named Eoannularidae.