sp. n. (Ascaridida: Subuluroidea), a parasite of spp. from Amazon rainforest, Brazil.

The parasite biodiversity of mouse opossums in Brazil remains incompletely explored. We describe a new species of (Ascaridida: Subuluroidea) from the large intestine of the white-bellied woolly mouse opossum, , based on the results of light and scanning electron microscopy (SEM). We also partially sequenced the mitochondrial cytochrome c oxidase I (MT-CO1) gene of the new species, using molecular phylogenetic analyses to determine its relationships within the Subuluroidea superfamily. As molecular data on subuluroid species are extremely limited, few inferences could be drawn from our phylogenies. Our SEM observations showed the detailed morphology of the cephalic extremity, precloacal pseudo-sucker, caudal papillae, phasmids and vulva. sp. n. differs from the other four parasites species of marsupials by the number of caudal papillae and the structure dimensions, and size of the spicule. Moreover, sp. n. has ten pairs of caudal papillae, which is unique compared to other species. We present morphometric and molecular data on this new species, contributing to future studies on subuluroids.