The phylum Myxozoa comprises more than 2180 species, almost all of which are considered to be obligate parasites of aquatic fishes. In the present study, Henneguya collaris sp. nov. is the first described histozoic myxozoan species of the genus Henneguya infecting the kidney of the greenband parrotfish Scarus collana (Actinopterygii, Scaridae). One hundred and eighty specimens of fish were collected randomly during the period from September 2014 to October 2015 from boat landing sites and the market places at Hurghada City along the Red Sea in Egypt. Of these, 90 (50 %) specimens were infected. Light microscopic examination showed that the infection was detected as mature spores with two polar capsules regularly arranged at the anterior pole of each spore and extruded polar filaments free in the kidney tissue. The spore body was oval in shape, measured 7.1 ± 0.2 (6.2-8.4) μm in length and 6.3 ± 0.2 (5.8-7.0) μm in width, with a bifurcated caudal process of equal length, reaching 6.3 ± 0.2 (5.8-7.0) μm in length. Polar capsules were 3.4 ± 0.2 (3.0-4.2) μm in length and 1.9 ± 0.2 (1.6-2.4) μm in width with 6-8 (10) turns of polar filaments. Ultrastructural analysis showed that the spore development was asynchronous. Sporogenesis, capsulogensis, valvogenesis, and spore maturation of the present parasite were also described. The present species was compared morphologically with the spore characteristics of the most similar species of Henneguya spp. recorded previously from different geographical areas taking into account the stage and dimensions of the spore body, tails, and polar filament coils, including their number and the most important characteristic features that distinguish them from the present species. Considering the data obtained, the material described herein represents a new species and the name Henneguya collaris sp. nov. is proposed.
Keywords: Henneguya collaris sp. nov.; Myxosporidiasis; Scarus collana fish; Ultrastructure.