A new species of Myxidium (Myxozoa) infecting the gallbladder of siluriform fish Pimelodus pantaneiro from the Brazilian Pantanal wetland

• First description of Myxidium pantanalense n. sp. infecting the gallbladder of Pimelodus pantaneiro from the Pantanal, Brazil. • Combination of morphological, molecular (SSU rDNA), and phylogenetic analyses for species identification. • Contribution to the knowledge of Myxidium diversity and distribution in South American freshwater environments. This study describes a new species of myxozoan, Myxidium pantanalense n. sp., parasitizing the gallbladder of the freshwater fish Pimelodus pantaneiro Souza-Filho and Shibatta, 2007, collected in the Brazilian Pantanal wetland, Mato Grosso do Sul State. The identification was based on morphological and molecular analyses. Myxospores exhibited a fusiform shape, 7-8 striations on the valvular surface, measuring 16.5 μm in length and 4.4 μm in width, with equally sized pyriform nematocysts measuring 5.5 μm in length and 2.8 μm in width, each containing a tubule making 4 to 5 turns. Phylogenetic analysis, based on small subunit ribosomal DNA sequences, positioned M. pantanalense n. sp. as the sister species to Myxidium amazonense . Morphological, genetic, and phylogenetic data support the designation of M. pantanalense n. sp. as a new taxon and expand the known diversity and geographic distribution of the genus Myxidium in South America.