Information on putative synapomorphies was used to distinguish between Dollfusentis, Illiosentis, and Tegorhynchus. Members of Tegorhynchus and Illiosentis possess a thick padlike vestibular muscle on the inner posterior wall of the trunk of female worms. The 2 genera differ in that the proboscis of members of Illiosentis have ventral hooks in the posteriormost circle that are greatly enlarged and male worms have a heavy muscular sheath covering the urogenital duct, both of which are absent in members of Tegorhynchus. Based on these features, Illiosentis is formally reestablished, and the diagnosis of the genus is emended. Dollfusentis is characterized by members having vestibular muscles that are bandlike rather than padlike, normal-sized hooks in the poster ring of the proboscis, and a crescent of 6 large hooks on the ventral proboscis, separated posteriorly from the posteriormost ring of hooks. The heavy muscular sheath covering the urogenital duct is not present in male worms of species of Dollfusentis. Type specimens of D. heteracanthus, originally described as I. heteracanthus but later transferred from Illiosentis to Dollfusentis, and the material included in a recent redescription of D. heteracanthus possess the padlike vestibular muscle, greatly enlarged ventral proboscis hooks in the posteriormost circle, and heavy muscular sheath covering the urogenital duct that is characteristic of other members of Illiosentis and lack the features characteristic of the other species assigned to Dollfusentis. Thus, D. heteracanthus is removed from Dollfusentis and reinstated as I. heteracanthus.

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