Prosthenhystera gattiin. sp. (Digenea: Callodistomidae), a gallbladder parasite ofBryconamericus ikaafrom the lower Iguazú River, described based on combined molecular and morphological evidence

Abstract

AbstractAdult forms of members of the Callodistomidae always parasitize the gallbladder of freshwater fishes and occur in Africa and America. This study provides a description of a new South American species belonging inProsthenhysterafrom the gallbladder of a characid fish (Bryconamericus ikaa), and ribosomal gene sequences (28S rDNA and ITS1-5.8S-ITS2) are used to demonstrate molecular differences between the new species and congeners as well as explore interrelationships among congeners. Additionally, the first cytological analysis is conducted for a member of the family to determine chromosome number and arrangement.Prosthenhystera gattiin. sp. most closely resemblesProsthenhystera caballeroiin morphology, but the vitellarium is more extensive reaching anterior to the caecal bifurcation in the new species and the uterus is confined to the hindbody inP. gattiin. sp., whereas it extends to the level of the pharynx inP. caballeroi. Also, the testes, cirrus sac, seminal receptacle and the ratio of body length to width are larger inP. gattiin. sp. Independent Bayesian inference analyses of 28S rDNA and ITS1-5.8S-ITS2 sequence fragments produced phylograms that showedP. gattiin. sp. is more similar toProsthenhystera obesa+Prosthenhystera oonasticathanP.caballeroi +two unidentified species ofProsthenhystera, but with poor posterior probability support for the node in the ITS1-5.8S-ITS2-based phylogram. Further, the genetic distance betweenP. oonasticaandP. gattiin. sp. are the largest amongProsthenhysteraspp. Cytological analysis revealed ten metacentric chromosomes, which is fewer than the 12–18 chromosomes present in species from the closely related Gorgoderidae.