[3] Hassalstrongylus dollfusi is a medium-sized nematode (3-10 mm in length), generally uncoiled, sometimes loosely coiled in 1–3 spirals.

[1]{[3]} According to Serrano et al. (2021), characters of Hassalstrongylus dollfusi males are: the morphology of the caudal bursa and the peculiar shape of the distal tip of the spicules.

Characters of the female are: the dorsal cuticular inflation at ovejector level and the subventral postvulvar alae supported by hypertrophied struts.

Hassalstrongylus dollfusi was first described in 1963[1] as a parasite of a wild house mouse, Mus musculus, in Venezuela and was never reported again for the next six decades.

In 2021 a paper based on a large survey of native rodents showed that the species was actually present as a parasite in five species of wild native cricetid rodents in Argentina: Oligoryzomys fornesi, Oligoryzomys flavescens, Oligoryzomys nigripes, Holochilus chacarius and Akodon azarae.