The first phylogenetic reconstruction of Nippostrongylinae (Nematoda: Heligmonellidae) reveals 3 new genera, the polyphyletic nature of Carolinensis and Vexillata, and identifies 5 clades with varying associations with mammals.

The Nippostrongylinae is a group of strongylid nematodes that includes species typically associated with coprophagous mammals; in the New World, it is represented by 82 species within 11 genera. Two main morphological features, the synlophe and the caudal bursa, are used to evaluate the characteristics that allow identification and classification of the organisms in the taxon. However, the analysis of these characters often requires a partial or total destruction of specimens and therefore morphological variation is studied in only a very small subset of organisms per species. To evaluate the phylogenetic signal from these characteristics, we use genetic data to reconstruct the first phylogeny for the Nippostrongylinae using nuclear and mitochondrial genes and include representatives of the most common and diverse genera. The reconstructed phylogeny features five distinct clades and allows us to identify three non-monophyletic taxa including Carolinensis, Vexillata and Hassalstrongylus. From these, Carolinensis s. l. is divided into four genera including Carolinensis, Boreostrongylus, Neoboreostrongylus n. gen. and Tepalcuanema n. gen. Stunkardionema is resurrected to include Vexillata noviberiae and Hassalstrongylus is divided into two, establishing Lovostrongylus n. gen. to include species that are closely related to Guerrerostrongylus and Trichofreitasia. Organisms in these three genera feature a caudal arrangement of type 2-2-1. Furthermore, species in Hassalstrongylus sensu stricto are more closely related to species in Malvinema and Stilestrongylus. Our results reveal the existence of an additional unnamed genus and underscore the usefulness of framing morphological characters in a comparative framework. A key for genera from the Americas is proposed.