Morphological and molecular characterization of the cryptic species Myxobolus cataractae n. sp. (Cnidaria: Myxozoa: Myxobolidae) parasitizing Imparfinis mirini (Siluriformes: Heptapteridae)

We describe Myxobolus cataractae n. sp., found parasitizing Imparfinis mirini from Cachoeirinha stream, a tributary of Pardo River, Paraná River basin, municipality of Botucatu, São Paulo State, Brazil. We based the description on myxospore morphology, histology, and small subunit ribosomal DNA partial sequences. Whitish and elongated mass of myxospores were found in gill filaments, occupying an intrafilamental position. The myxospores were slightly ellipsoidal and the morphometric measurements revealed a myxospore body length of 7.8 ± 0.4 μm; myxospore width of 5.9 ± 0.4 μm; and thickness of 3.9 ± 0.3 μm. The polar capsules are equal in size and measured 3.5 ± 0.2 μm in length and 1.7 ± 0.2 μm in width. The polar tubules had 6–7 coils. Myxobolus cataractae n. sp. is classified as the intrafilamental type and chondreal subtype by the histological analysis of gills. Phylogenetic analysis showed a well-supported subclade formed by species that parasitize gills of Siluriformes, with M. imparfinis as a sister species of Myxobolus cataractae n. sp. Using molecular and morphological characterization, this cryptic species was identified as a new species of the genus Myxobolus. [Display omitted] •A new myxosporean species is described from gill lamellae of Imparfinis mirini;•Histological analysis showed chondrocyte degradation and lamella deformations;•A new species was denominated Myxobolus cataractae n. sp.;•This research contributes to the knowledge of myxosporean diversity in South America.