Supplemental description of Stephanoprora ornata Odhner, 1902 (Digenea: Echinochasmidae) infecting the Nile crocodile, Crocodylus niloticus (Crocodylidae) from Namibia with emendation of Mesorchis Dietz, 1909 and a phylogenetic analysis.

The synonymies of the echinochasmid genera Mesorchis Dietz, 1909 and Monilifer Dietz, 1909 with Stephanoprora Odhner, 1902 remain contentious and unresolved with morphology. To explore the matter, we herein provide a supplemental description of the type species of Stephanoprora, Stephanoprora ornata Odhner, 1902, based on specimens we collected from the intestine of a Nile crocodile Crocodylus niloticus Laurenti, 1768 (Crocodylia: Crocodylidae) captured in the Kavango River, Namibia. No nucleotide information was available previously for S. ornata. Morphology plus 28S and ITS2 phylogenetic analyses suggested Stephanoprora is a monotypic genus that can be differentiated from other genera by having 26 collar spines. Stephanoprora differs from Mesorchis by the number and distribution of collar spines (26 [2 dorsal spines, 12 lateral spines, 12 corner spines] vs. 22 [2 dorsal spines, 12 lateral spines, 8 corner spines] in Mesorchis), length of the pre-pharyngeal oesophagus, pharynx position posterior to collar (vs. pre-pharyngeal oesophagus short, pharynx anterior to or at level of corner spines), and testes shape (elongate-ovoid, irregular in outline vs. ovoid, atypically elongated). Our 28S and ITS2 phylogenies recovered the new sequence of S. ornata (having 26 collar spines) sister to all remaining echinochasmid sequences, representing species that have 20-24 collar spines. Echinochasmus Dietz, 1909 and Mesorchis were recovered as paraphyletic. We retain Monilifer as a junior subjective synonym of Echinochasmus based a suite of morphological features related to body shape and genitalia and because the designated type for Monilifer was reassigned to Echinochasmus. We accept 25 species of Mesorchis.