Morphology and phylogeny of a novel Ortholinea (Cnidaria: Myxozoa) species in the neotropical fish Batrachoides surinamensis, Bloch and Schneider, 1801 (Batrachoidiformes: Batrachoididae).

The Brazilian Amazon estuary is a highly dynamic environment, characterized by substantial organic matter input and a rich diversity of fish species that utilize this ecosystem for feeding and reproduction. Despite its ecological relevance, ichthyo-parasitological research in the region remains limited, particularly regarding the diversity of parasitic species within the class Myxozoa. Among the fish species for which parasitological data are still scarce is the Pacamã frogfish, Batrachoides surinamensis (Bloch and Schneider, 1801), a demersal species that feeds on small invertebrates and fish. The present study describes the morphological, molecular and phylogenetics aspects of Ortholinea abadiensis n. sp., a new species isolated from the urinary bladder of the B. surinamensis, collected on the coast of the Brazilian Amazon. Myxospores were observed dispersed in the liquid of the urinary bladder in 16 of the 20 specimens (80 %) of the specimens analyzed. The myxospores were subspherical with 18 to 20 superficial ridges and measured, 6.7±0.2 (6.3-7.1) µm in length, 6.0±0.5 (5.6-6.5) µm in width, and 6.1±0.1 (5.9-6.2) µm in thickness. The polar capsules were symmetrical and semispherical, with openings in opposite directions to the valves, which were 2.6±0.2 (2.2-3.2) µm in length and 2.4±0.1 (2-2.6) µm in width, with 5 to 6 turns of polar tubules. Morphometrically and morphologically, this species was distinct from other previously described Ortholinea. In the SSU rDNA phylogeny, O. abadiensis was positioned within a clade comprising marine species, with O. nupchi identified as its sister species. This study provides new morphological and molecular insights into a new species of the genus Ortholinea in a fish with a wide geographic distribution in South America.