• DNA barcoding
• protist

Recent investigations have suggested the feasibility of establishing a species identification system reliant on the analysis of the sequence of the mitochondrial cytochrome c oxidase subunit 1 gene (cox1), the DNA barcoding tool. I assessed the effectiveness of this procedure in the most cosmopolitan, ubiquitous, and differentiated group of ciliated protists, the genus Euplotes. The availability of the largest collection of Euplotes living strains which currently exists worldwide, the result of half a century of sampling at all latitudes of the globe, allowed me to help create the basis for making this evaluation. Accordingly, I analyzed cox1 gene sequences from 81 strains belonging to 15 Euplotes species representatives of different habitats. All Euplotes strains analyzed were correctly partitioned into the 15 species, whose interspecific cox1 sequence divergence was about 60%, whereas the intraspecific sequence divergence ranged from 0.5% to 43%. Moreover, some species not only showed higher values of cox1 intraspecific divergence, but also their representative strains did not cluster together on the cox1 phylogenetic trees, suggesting the occurrence of cryptic species. Overall, my study demonstrates the feasibility of the DNA barcoding procedure to the genus Euplotes.