Hoferellus matosi sp. nov. (Bivalvulida: Myxobilatidae) parasitizing Ageneiosus ucayalensis Castelnau (Siluriformes: Auchenipteridae) from the Coaracy Nunes Hydroelectric Reservoir in Amap, Eastern Amazon, Brazil.

The microparasite species Hoferellus matosi sp. nov. was found parasitizing the urinary bladder of the fish species Ageneiosus ucayalensis collected from the Coaracy Nunes hydroelectric reservoir in Ferreira Gomes, Amap, Brazil. Plasmodia and myxospores were identified in fragments of the urinary bladder and characterized through microscopic and molecular analyses. Myxospores were subspherical in sutural view, with fine striations or projections on the posterior portion of the valves, measuring an average length and width of 8.5 (8.28.8) m and 7.9 (7.68.2) m, respectively. Each spore contained two ovoid polar capsules of equal size, with an average length and a width of 3.4 (3.23.6) m and 3.1 (2.93.3) m, respectively. Comparing a partial sequence (1,153base pairs) of the small subunit ribosomal DNA gene revealed that H. matosi sp. nov. is clearly distinct from other Hoferellus species deposited in the GenBank, as confirmed through a phylogenetic analysis using Bayesian inference. A morphometric analysis also supported this distinction. Therefore, H. matosi sp. nov. is a newly identified myxosporean species that clusters with H. azevedoi, H. tartarugualis, and H. jutubensis in the phylogenetic tree, forming a distinct lineage of Amazonian Hoferellus.