Diversity of Nippostrongylinae (Heligmonellidae) in the Amazon Basin: Hypocristata riopardensis n. sp. reveals evolutionary link and provides insights into molecular evolution

Knowledge of helminth diversity in sigmodontine rodents from the Amazon remains limited, particularly in transitional zones between forested and human-modified environments.During a survey of the parasitic fauna of Neacomys guianae in the Rio Pardo rural settlement, Amazonas, nematodes exhibiting unique morphological and genetic traits were discovered.Detailed morphological analyses, including examination of the cephalic region, synlophe, oesophageal structures, copulatory bursa, and reproductive system, revealed diagnostic features that do not correspond to any species previously described for the genus Hypocristata.Complementary sequencing of the 28S ribosomal RNA gene confirmed the placement of the specimens within the Nippostrongylinae and indicated a phylogenetic position closely related to Lovostrongylus sp. and Guerrerostrongylus marginalis, while still forming a polytomy.Together, the morphological and molecular evidence supports the establishment of Hypocristata riopardensis n. sp., expanding the recognized diversity of this lineage.The discovery highlights the relevance of integrative taxonomic approaches for understanding evolutionary relationships and host-parasite associations in Amazonian ecosystems.This study contributes to the growing body of knowledge on Neotropical nematode diversity and provides a foundation for future investigations into the ecological and evolutionary dynamics of Nippostrongylinae.