Henneguya adherens n. sp. (Myxozoa, Myxosporea), parasite of the Amazonian fish, Acestrorhynchus falcatus.

A new species of myxosporean from the gill filaments of the freshwater teleost fish, Acestrohynchus falcatus collected in the Amazon river is described from light and transmission electron microscope observations. The mature spores (total length 32.3 [30.7-35.1] micron) and all developmental stages were found in the same sporogonic plasmodium. The ellipsoidal spore body consists of 2 unequal shell valves adhering together along the suture lines. Each valve, tapering as a caudal projection, forms a long tail (length 20.5 [18.0-21.7] micron). The tail was surrounded by a homogeneous sheath on its length. The polar capsules measuring 3.1 x 1.2 micron contain 3-4 coils of the polar filament. All surfaces of the immature and mature spores were surrounded by a closely adherent homogenous structural sheath, mainly thicker around the tails. The taxonomic affinities of this parasite to other species are discussed.