We describe a new species of the genus Alippistrongylus (Nematoda: Trichostrongylina) in the small intestine of Delomys dorsalis (Rodentia: Sigmodontinae) found in Itatiaia National Park (Parque Nacional do Itatiaia, PNI), state of Rio de Janeiro, Brazil. The new species can be distinguished between the other two species previously described by the following morphological characteristics: pattern of the rays from the caudal bursa rays in males and the spherical-shaped appendage in the female. Additionally, we provide molecular genetic data from the new species. The discovery of Alippistrongylus itatiaiaensis sp. n. expands our understanding of nematode diversity and underscores the importance of parasite studies in biodiversity conservation. Its occurrence in a preserved area like the PNI emphasises the role of such habitats in maintaining unique ecological interactions.
