We used scanning electron microscopy (SEM) to establish species-specific sets of characters for protonymphon larvae of two representatives of the ‘patagonica’ species group of Pallenopsis, P. patagonica and P. yepayekae. The larvae of both species are ‘typical’ protonymphon larvae sensu Bain (2003). Despite the close relationship of the two species, we observed numerous features that allow for differential diagnosis, e.g. general habitus, the number, arrangement and branching type of setules, the armature of the movable and immovable chelifore fingers, and the shape of the dactylus and setules of appendages II and III. SEM is particularly suitable for visualising these features. Our results further support the idea that protonymphon larvae can be identified to species level when adequate imaging techniques are used, as is also the case for larvae of other arthropods. Moreover, the status of the two studied species of Pallenopsis is fully supported by protonymphon larval morphology.