PHYLOGENETIC-RELATIONSHIPS OF THE NASSULIDA WITHIN THE PHYLUM CILIOPHORA INFERRED FROM THE COMPLETE SMALL-SUBUNIT RIBOSOMAL-RNA GENE-SEQUENCES OF FURGASONIA-BLOCHMANNI, OBERTRUMIA-GEORGIANA, AND PSEUDOMICROTHORAX-DUBIUS

Using comparisons of complete small subunit rRNA sequences from the ci liated protozoans Furgasonia blochmanni, Obertrumia georgiana, and Pse udomicrothorax dubius we inferred the phylogenetic position of the Nas sulida (Class Nassophorea) within the Ciliophora. In distance matrix a nalyses the Nassulida share a common ancestry with the colpodean cilia te Colpoda inflata. Distance matrix and parsimony methods convincingly demonstrate that the Nassulida plus Colpodida are members of a comple x ciliate assemblage that also includes the oligohymenophorans and phy llopharyngeans. These phylogenetic inferences are largely congruent wi th recent analyses of 23S-like rRNA gene sequences and morphogenetic f eatures. Groups traditionally thought to represent ancestral lineages now appear as highly derived ciliates. In contrast, heterotrichs which were considered to represent a highly evolved group, diverge at the b ase of the ciliates.