Description of a new species of Therodamas (Crustacea: Ergasilidae) from the gills of Trachelyopterus galeatus (Auchenipteridae) from the Brazilian Amazon.

Therodamas comprises copepods that parasitize marine, brackish-water and freshwater fishes, and currently includes eight valid species. In this study, a new species for this genus was described from the gills of Trachelyopterus galeatus collected in the Jari River, eastern Amazon, Brazil. Parasites were analyzed using light microscopy, scanning electron microscopy and SSU-rDNA sequences. A total of 539 parasites has recovered, with prevalence of 69%, mean intensity of 18 parasites per host and mean abundance of 12 (standard deviation = 12.8). The new species, Therodamas anujauensis n. sp., is characterized by the absence of cephalic lobes, an elongated neck and a distinctive combination of setae and spines on the swimming legs. Phylogenetic analyses confirmed its placement within Ergasilidae and revealed a close relationship with Therodamas longicollum. Molecular dating suggested that the Therodamas lineage originated approximately 59.6 million years ago, whereas the divergence between T. anujauensis n. sp. and T. longicollum occurred about 6.03 million years ago. This study increases the number of known species of Therodamas from eight to nine and expands knowledge of parasite diversity in the Amazon region.