Taxonomic affinities of Cryptocaryon irritans and Ichthyophthirius multifiliis inferred from ribosomal RNA sequence data

Abstract

Comparison of partial sequences of the 18s rRNA gene of the parasitic ciliates Cryptocaryon irritans and lchthyophthlr~us rnultifilijs confirmed that these taxa are not as closely related as was first thought. Phylogenetic trees generated from sequence data grouped I. rnultifiliis with 3 species of Tetrahyrnena, supporting the existing taxononlic classification of these 2 genera together in the Order Hymenostomatida, Class Oligohymenophora. In contrast, C. irritans was grouped wlth Colpoda inflata (Class Colpodea) supporting the theory that the l ~f e cycle and morphological similarities evident between I. multifiliisand C. irritans a r e a n example of convergent evolution.