PHYLOGENETIC-RELATIONSHIPS BETWEEN THE ACANTHAREA, AND THE POLYCYSTINEA - A MOLECULAR PERSPECTIVE ON HAECKEL RADIOLARIA

Polycystine radiolaria are among few protistan groups that possess a c omprehensive fossil record available for study by micropaleontologists . The Polycystinea and the Acantharea, whose skeletons do not become f ossilized, were once members of the class ''Radiolaria'' (''Radiolaria '' sensu lato: Polycystinea, Phaeodarea, and Acantharea) originally pr oposed by Haeckel but are now included in the superclass Actinopoda. P hylogenetic relationships within this superclass remain largely enigma tic. We investigated the evolutionary relationship of the Acantharea a nd the Polycystinea to other protists using phylogenetic analyses of 1 6S-like ribosomal RNA (rRNA) coding regions. We circumvented the need to culture these organisms by collecting and maintaining reproductive stages that contain many copies of their genomic DNA. This strategy fa cilitated extraction of genomic DNA and its purification from symbiont and prey DNA. Phylogenetic trees inferred from comparisons of 16S-lik e coding regions do not support a shared history between the Acanthare a and the Polycystinea. However, the monophyly of the Acantharea and t he separate monophyly of the Polycystinea (Spumellarida) are well supp orted by our molecular-based trees. The acantharian lineage branches a mong crown organisms whereas the polycystine lineage diverges before t he radiation of the crown groups. We conclude that the Actinopoda does not represent a monophyletic evolutionary assemblage and recommend th at this taxonomic designation be discarded.