Integrative taxonomy reveals a novel Ceratomyxa (Cnidaria: Myxozoa) parasitizing the gallbladder of the Amazonian fish Pellona castelnaeana.

Freshwater species of the myxozoan genus Ceratomyxa have recently emerged as a diverse group of parasites infecting fish in South America, many of which exhibit vermiform plasmodia with dynamic motility. In this integrative taxonomic study, we describe Ceratomyxa souzapintorum n. sp., a novel species infecting the gallbladder of the Amazonian clupeiform fish Pellona castelnaeana. The prevalence of infection was 73%, and the parasite displayed worm-like plasmodia exhibiting nematode-like motility. Arcuate myxospores measured 14.8 ± 1.7 µm in thickness and 6.1 ± 0.7 µm in length, with a posterior angle of 59° (42-78°). The two spherical nematocysts measured 2.0 µm and contained filaments with 3-4 coils. Ultrastructural analyses revealed plasmodia consisting of an outer cytoplasmic region containing sporogonic stages and numerous tubular mitochondria, and internally a large central vacuole. Mature plasmodia exhibited a thin cytoplasmic layer, with mature myxospores apparently free within the central vacuole. Phylogenetic analyses positioned C. souzapintorum n. sp. within the clade of Amazonian Ceratomyxa species.