ABSTRACT: Comparison of partial sequences of the 18S rRNA gene of the parasitic ciliates Cryptocaryon irritans and Ichthyophthirius multifiliis confirmed that these taxa are not as closely related as was first thought. Phylogenetic trees generated from sequence data grouped I. multifiliis with 3 species of Tetrahymena, supporting the existing taxonomic classification of these 2 genera together in the Order Hymenostomatida, Class Oligohymenophora. In contrast, C. irritans was grouped with Colpoda inflata (Class Colpodea) supporting the theory that the life cycle and morphological similarities evident between I. multifiliis and C. irritans are an example of convergent evolution.

KEY WORDS: Cryptocaryon irritans . Ichthyophthirius multifiliis . 18S rRNA gene . Molecular taxonomy

Published in DAO Vol. 22, No. 1 (1995) on May 4
ISSN: 0177-5103. Copyright © Inter-Research, Oldendorf/Luhe, 1995