Abstract
This paper describes 2 new myxosporean species, Henneguya lepturus sp. nov. and Thelohanellus lepturus sp. nov., simultaneously infecting the brain and spinal cord of Hypopygus lepturus Hoedeman, 1962 (Teleostei, Hypopomidae) from the Brazilian Amazon (Roraima State). Several spherical cysts of varying dimensions (up to 135 mu m) were microscopically observed. The myxospores of H. lepturus sp. nov. measured 25.8 mu m in total length, having an ellipsoidal body (12.4 x 6.4 x 2.2 mu m) and 2 equal tapering tails (13.4 mu m in length). Each of the 2 pyriform polar capsules measured 4.4 x 1.6 mu m and possessed a polar filament coiled in 8-9 turns. The myxospores of T. lepturus sp. nov. were pyriform, formed by 2 equal valves (17.7 x 9.1 x 4.3 mu m) surrounding a single polar capsule (10.9 x 3.5 mu m) that had a coiled polar filament with 13-16 turns and a binucleated sporoplasm that contained several circular sporoplasmosomes. Molecular analysis of the small subunit (SSU) rRNA gene sequences of these 2 species were in agreement with the taxonomic classification derived from the ultrastructure of the myxospores. Histopathology of the host tissue showed degradation of the myelinated axons surrounding the cysts of both species, with the hosts displaying behavioural changes and erratic movements when observed in an aquarium.