Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)During a survey of myxozoan parasites of freshwater fish from the Mogi Gua double dagger u River in So Paulo State, Brazil, plasmodia of Henneguya visibilis n. sp. were found on the fins of Leporinus obtusidens (Characiformes: Anostomidae). The plasmodia, which were observed on five out of eight (62.5 %) L. obtusidens examined, were 400-1,000 mu m long. Mature spores were elongated with a spore body 10.8 +/- 0.6 mu m long and 3.9 +/- 0.2 mu m wide, a caudal process 18 +/- 1.2 mu m long, and a total spore length of 26.8 +/- 1.1 mu m. Polar capsules were elongated 4.9 +/- 0.3 mu m long and 1.4 +/- 0.1 mu m wide. Histological examination indicated that the plasmodia developed in the connective tissue, and no inflammatory infiltrate was observed at the infection site. Ultrastructural analysis showed a plasmodium wall with a single membrane and several pinocytotic canals. Sporogenesis occurred from the periphery to the center of the plasmodia. Phylogenetic analysis of the 18S rDNA sequence using maximum likelihood and maximum parsimony methods showed H. visibilis n. sp. positioned in a sub-clade composed of Henneguya/Myxobolus parasites of several freshwater fish families.11318190Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)CNPq [477658/2010-5]