A knowledge of the process of chamber formation in foraminifera is important for understanding growth and development, and provides evidence about taxonomic relationships. Significant differences in the processes of chamber formation and calcification are known between species with porcelaneous tests and those with calcareous hyaline tests.

For this study, a video camera with a microscope attachment was used to record chamber formation in Archaias angulatus. Detailed study of the recording revealed previously undescribed transitional stages prior to calcification of the test wall. Chamber morphogenesis in Archaias angulatus was also compared to published descriptions of growth in other species of foraminifera. The formation of an anlage in Archaias angulatus, prior to membrane secretion and calcification of the test wall, is unlike other Milioliina that have been studied, and similar to the anlage formation in species of Rotaliina and Globorotaliina. This suggests a possible route for evolution of calcareous hyaline tests from the Milioliina.

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