Phylogenomics corroborates morphology: New discussions on the systematics of Trichostomatia (Ciliophora, Litostomatea)

•First phylogenomic study discussing the traditional systematics of the subclass Trichostomatia.•Proposition of a new Ophryoscolecidae genus, Dagostonium.•Transfer of Monoposthium cynodontum into the genus Cycloposthium. The subclass Trichostomatia (Ciliophora, Litostomatea) constitutes a well-supported monophyletic group, which includes ciliates exclusively found as symbionts of vertebrates, primarily herbivorous mammals. Recent molecular analyses reinforce the subclass monophyly, though almost all orders, suborders, families, and genera are found to be non-monophyletic. Here, we reconstructed the evolutionary history of the subclass Trichostomatia using a phylogenomic approach and discussed some systematic inconsistencies. We propose a new Ophryoscolecidae genus, Dagostonium, to include Diplodinium polygonale. Monoposthium cynodontum is transferred to the genus Cycloposthium.