Small subunit ribosomal RNA sequences of Phaeodarea challenge the monophyly of Haeckel's Radiolaria

Abstract

In his grand monography of Radiolaria, Ernst Haeckel originally placed Phaeodarea within the class Radiolaria, together with Acantharea and Polycystinea. Cytological and ultrastructural studies, however, questioned the monophyly of Radiolaria, suggesting the independent evolutionary origin of the three taxa. Some recent molecular analyses based on small subunit ribosomal RNA (SSU rRNA) sequences challenged this classification, supporting the sisterhood of Acantharea and Polycystinea. In order to further test the monophyly of all Haeckel's Radiolaria, and as no data on Phaeodarea were available, we sequenced the complete SSU rRNA gene of three Phaeodarea and three Polycystinea. Our analyses show that the monophyletic Phaeodarea clearly branch among Cercozoa, and confirm that Acantharea and Polycystinea share a common history. This result enhances the morphological variability within Cercozoa, a phylum already containing very heterogeneous groups of protists. Our study suggests that the ability to secrete SrSO4 and the organization of microtubules inside axopodia are better phylogenetic markers than the simple presence of a central capsule and axopodia.