New species of Ellipsomyxa (Bivalvulida: Ceratomyxidae) parasitizing the gallbladder of Ageneiosus ucayalensis (Siluriformes: Auchenipteridae) in the Brazilian Amazon region.

The present study describes a new myxozoan species, Ellipsomyxa matosi n. sp. infecting the gallbladder of the catfish Ageneiosus ucayalensis, on Jutuba Island, municipality of Belém, state of Pará, Brazil. The new species was diagnosed based on morphological and molecular analyses. 33 specimens were examined between February and May 2023, and all (100 %) presented disporic plasmodia in the bile fluid, with ellipsoidal, slightly elongated mature myxospores, with a subtle valve projection in the apical region and a curved suture line, typical morphological characteristics of the genus Ellipsomixa. The polar capsules were pyriform and of equal size, with a subterminal opening and 6-7 polar tubule coils. No histopathological changes, lesions, or inflammatory responses were observed in the epithelial layer or any part of the tissue. PCA identified the proximity in spore length (SL) of the new species to E. amazonensis and E. papantla. The partial SSU rDNA sequence obtained was distinct from all other available sequences from species of this genus. The phylogenetic analysis obtained high nodal support, grouping the new species as an ancestor of the well-defined clade of Ellipsomyxa species described in the Amazon region.