Morphological and Phylogenetic Features of Ceratomyxa macapaensis n. sp. (Myxozoa: Ceratomyxidae) in Mesonauta festivus Heckel, 1840 (Cichliformes: Cichlidae) from the Eastern Amazon Region.

PURPOSE The class Myxozoa consists of microscopic spores that typically present uniform morphological simplifications, containing one or two sporoplasms surrounded by valve cells. The present study analysed the morphological and phylogenetic characteristics of what proved to be a new species of Ceratomyxa found in the gallbladder of Mesonauta festivus Heckel, 1840 captured on the Piririm River in the municipality of Macapa, in Amapa state, Brazil. METHODS The fish were collected in gillnets, and were transported alive to Amapa State University in Macapa for the analysis of the organs. Crescent- or arch-shaped free spores were observed under light microscopy, containing two polar capsules and a suture line, which is typical of the morphology of the genus Ceratomyxa, contained within plasmodia that had snake-like movements. The gallbladder was conserved in 80% alcohol for the analysis of the 18S rDNA gene, and in Davidson solution for standardhistology. RESULTS Ceratomyxa spores (n = 20) were observed in 11 of the 50 samplesanalysed, and thus had a prevalence of 22%, and had a mean length of 4.2 ± 0.5 µm, mean thickness of 22.75 ± 0.3 µm, and two polar capsules, 1.86 ± 0.3 µm long and 1.63 ± 0.1 µm thick. CONCLUSIONS The phylogenetic analysis indicated that the new species forms a cluster with other freshwater Amazonian Ceratomyxa species, described previously. The new species represents the first description of a taxon of the genus Ceratomyxain fish from the Brazilian state of Amapa.