Abstract
The tapeworm genus Mariauxiella (Onchoproteocephalidea, Proteocephalidae) was recently revised and its species composition reappraised; however, its actual species diversity remains incompletely understood. In the present study, an integrative taxonomic approach combining morphological, ultrastructural, and molecular phylogenetic analyses was applied to proteocephalid tapeworms collected from the driftwood catfish Ageneiosus militaris (Siluriformes: Auchenipteridae) in the Upper Paraná River basin, Brazil. The evidence obtained supports the proposal of Mariauxiella saltogrande n. sp. , the third species assigned to the genus. The new species can be differentiated from the most similar species, Mariauxiella brevifilis , by its body size, proglottis width, scolex shape, and the arrangement of the osmoregulatory canals in the proglottides. Phylogenetic analyses based on the partial large subunit nuclear ribosomal RNA (RNA28S) and the complete mitochondrial cytochrome c oxidase subunit I (MT-CO1) sequence data strongly supported the monophyly of Mariauxiella and recovered Mariauxiella saltogrande n. sp. as sister to M. brevifilis . The discovery of this new species expands the known diversity of Mariauxiella and provides further evidence for the usefulness of integrative taxonomy in resolving species boundaries and evolutionary relationships among Neotropical proteocephalids.