ABSTRACT: The morphological similarities of the outer and inner test structure of primitive and advanced Fusulinoida (Tournayellida, Endothyrida, Fusulinida) and primitive and advanced Miliolata (Baisalinidae, Ophthalmidiidae, Miliolidae, Alveolinina, Soritinida) have been traditionally viewed as a result of convergent evolution.Adetailed comparison of the test and apertural shape, of the inner supplementary deposits of the test material (mounds, nodes, spine like projections, nodosities and teeth and flaps in the thin sections) of the both taxonomic groups studied, as well as the comparison of the fusulinacean wall with newly discovered unique ultrastructural features of the porcelaneous wall of largeAntarctic miliolids (along with the highmagnesium level in the both calcareous groups) lead us to an understanding of their close relationship. Both groups represent two smaller branches of one phylogenetic lineage and hence the similarity of the outer and inner structures of their shells could be considered as parallelism in the closely related groups.