Molecular phylogeny of Chonotrichia (Ciliophora, Phyllopharyngea) inferred from SSU rDNA sequences

The ciliophoran taxon Chonotrichia Wallengren, 1895 are epibionts typically on Crustacea. There are about 112 species reported from all around the world. These species are known essentially from microscopical observations, and molecular data are far from sufficient, which largely hinders the study on their phylogenetic relationships. Here, we present the complete small-subunit (SSU) rDNA sequences of three species from Roscoff, Brittany, France, and one from Switzerland. These sequences are used to analyze the phylogentic relationships of the Chonotrichia, covering all three controversial orders, Exogemmida Jankowski, 1972, Cryptogemmida Jankowski, 1975, and Chilodochonida Batisse, 1994, for the first time. The phylogenetic tree confirms that all chonotrich sequences group together, nested in the dysteriid sequences. The tree topology also shows the separation of the chilodochonids from Exogemmida, supporting the establishment of the order Chilodochonida.