A new Ceratomyxa (Cnidaria: Myxosporea) infecting the ornamental fish species Pterophyllum scalare from the Amazon Region, Brazil.

A new parasite of the Class Myxozoa is described in the gallbladder of the ornamental angelfish Pterophyllum scalare, in two municipalities in the state of Amapá, Brazil, based on morphological, morphometric and phylogenetic descriptions. From October 2022 to August 2024 fifty-five angelfish specimens were sampled in Macapá (n=10) and Tartarugalzinho (n=45). Slightly arched mixospores were observed by light microscopy and had characteristics consistent with those of the genus Ceratomyxa. These obtained an average length of 1.6 ± 0.2 µm and 11.5 ± 1.1 µm in thickness. The polar capsules were subspherical and 0.7 ± 0.1 µm long and 0.6 ± 0.1 µm wide, with 3 to 4 turns of the polar filament. Phylogenetic analysis showed that the new species is grouped in the family Ceratomyxidae, in addition to being positioned in the same subclade of freshwater ceratomyxids from the Brazilian Amazon, demonstrating that this species shares a common ancestor with its close relatives, based on geographic affinity. Ceratomyxa tavariensis n. sp. is the first species of the class Myxozoa described infecting angelfish in Brazil, and the thirteenth species of Ceratomyxa described in the country.