Size does not matter: molecular phylogeny reveals one of the largest trematodes from vertebrates, the enigmatic , as a species of (Trematoda: Clinostomidae).

Despite the recent advances raised in the molecular era to the taxonomic knowledge of species of the family Clinostomidae, especially those belonging to the specious genus , some groups of these vertebrate parasites remain poorly studied. This is the case of species of the enigmatic genus Witenberg, 1926, until recently monotypic and restricted to South America, but with its occurrence expanded to North America after the description of . Rosser et al., 2020. Nevertheless, molecular data for the type species of the genus, (Diesing, 1850), is lacking so far. In the present study, large clinostomid metacercariae morphologically indistinguishable from were obtained from two erythrinid fishes from the Rio Doce River, Southeast Brazil. Samples of the parasites were subjected to a multigene (28S rDNA, ITS and 1) molecular characterization followed by phylogenetic reconstructions. Phylogenies based on single-gene and concatenated datasets revealed unequivocally that falls in a well-supported clade together with species of the genus . Moreover, the molecular divergences observed in relation to spp. [ranges of 2.4-6%, 2.4-3.8% and 14.7-19.3% for the ITS, 28S and 1 genes, respectively] are compatible with a congeneric status with these species. Therefore, the genus is here synonymized with Leidy, 1856 and (Diesing, 1850) Braun, 1899 re-established. In the phylogenetic analysis, the recently described '' , presented as an isolated, independent lineage, showing significant molecular divergences to (12.6%, 7.6%, 18,6% for the ITS, 28S and 1 genes, respectively). However, given the complex scenario raised in the morphology-based taxonomy of Clinostomidae, we took a conservative approach by not proposing a new genus to '.' until molecular data of other clinostomid genus from birds, , become available. Data here presented reveals that body size is not a useful criterion for higher-level classification in Clinostomidae. Finally, we highlighted the importance of the availability of molecular data for the type species of trematode genera proposed from South America to support a trans- or intercontinental distribution.