Ultrastructural and phylogenetic data of Chloromyxum riorajum sp. nov. (Myxozoa), a parasite of the stingray Rioraja agassizii in Southern Brazil.

We describe a new myxozoan parasite found infecting the gall bladder of the cartilaginous fish Rioraja agassizii (Rajidae) from the South Atlantic coast of Brazil. Light microscopy, scanning and transmission electron microscopy and phylogenetic data were used. Numerous irregular polyspqric plasmodia externally covered by numerous microvilli containing different stages of sporogony, including free spores, were observed in bile. Ellipsoidal spores, on average 11.41 microm long, 8.48 microm wide and 7.32 microm thick, were formed by 2 equal-sized valves, each possessing 3 to 4 (rarely 5) elevated ridges which projected from the basal portion of the spore, and joined along a sinuous S-shaped sutural line. The basal portion of the valves bore a bundle of 33 to 37 extended tapering caudal filaments attached to the basal portion of the last ridge and basal portion of the sutural edge of the 2 valves. The caudal filaments, formed of material similar to the valves, were attached to the shell wall by a conical basis. The spores contained 4 equal-sized pyriform polar capsules (4.5 x 2.4 microm), located at the same level, each with a polar filament with 6 (rarely 7) coils. Binucleate sporoplasm was irregular in shape, with a granular matrix and dense bodies randomly distributed in a light area. Based on the shape and dimensions of the spore, on the number, position and arrangements of the surface ridges, caudal bundle of filaments, polar capsules and polar filament arrangements, as well as phylogenetic analyses using the small subunit ribosomal DNA (SSU rDNA) sequences, we propose the name Chloromyxum riorajum for this new myxozoan.