Morphology, ultrastructure and phylogeny of Myxobolus curimatae n. sp. (Myxozoa: Myxosporea) a parasite of Prochilodus costatus (Teleostei: Prochilodontidae) from the São Francisco River, Brazil.

Myxobolus curimatae n. sp. has been found infecting the gill filaments of Prochilodus costatus (Prochilodontidae) from the São Francisco River in the state of Minas Gerais, Brazil. The prevalence of the species was 18.7%. Mature spores were rounded from a frontal view, with elongated polar capsules of equal size, and had polar filaments with 9-10 turns. Ultrastructural analysis revealed that sporogenesis patterns followed those of other Myxobolus species. The plasmodium walls had numerous invaginations and protrusions, and few pinocytic channels. Numerous mitochondria, generative cells and young pansporoblasts were observed in the peripherical areas of the plasmodia, and mature spores were found in deeper layers. A layer of collagenic fibrils surrounded the plasmodia. The morphological data and molecular analysis of the 18S rDNA identified this parasite as a new species. The maximum likelihood phylogenetic tree showed M. curimatae n. sp., as a sister species of Thelohanellus marginatus, in a basal branch of the subclade composed by parasites with tropism to different organs and host families.