Currently, there are 6 recognized species in the genus Rhopalias. These parasites are found in the small intestines of numerous species of marsupials throughout North and South America. Small mistakes in various classical taxonomic works have given rise to recent and numerous misidentifications of these species. In this work, we examine a total of 99 specimens across all species from museum collections in an attempt to determine informative taxonomic characters to distinguish these species. Despite confusion in the literature, accurate identification of these species can be achieved by observing the presence or absence of oral and flanking spines anterior to the oral sucker.