Morphological and molecular characterisation of Henneguya pallida n. sp. from the gills of the pale catfish, Rhamdia guatemalensis (Günther, 1864), in southern Mexico

During a survey on myxozoan parasites in fish from southern Mexico, myxospores from the genera Henneguya and Myxobolus were detected in the gills and mesentery of the pale catfish ( Rhamdia guatemalensis ). Identification of a Henneguya sp. in the gills was supported by histology, myxospore morphology, and molecular analyses of the 18S rDNA and 28S gene sequences. Histopathological examination revealed that the myxospore-forming plasmodia of Henneguya sp. were associated with the gill filaments. Phylogenetic analyses placed this species within a clade of Henneguya species infecting Siluriformes. In contrast, scattered myxospore aggregates found in the mesentery were examined solely through morphological criteria. Four different myxospore morphotypes belonging to the family Myxobolidae were identified in a single specimen of R . guatemalensis ; however, molecular identification was unsuccessful; therefore, only brief taxonomic descriptions are provided. Based on morphological and molecular evidence, the Henneguya sp. from the gills is described as a new species, Henneguya pallida n. sp. Further samplings are needed to fully characterise the myxospores found in the mesentery. • Henneguya pallida n. sp. infects the gills of Rhamdia guatemalensis • Plasmodia of H. pallida n. sp. are located in the middle zone of the hemibranchs • Histology shows H. pallida n. sp. in multilayered epithelium of gill filaments • The 18S and 28S rDNA sequences of H. pallida n. sp. were analysed • Four myxospore morphotype were found in the mesentery