Description of a new species of Aethycteron Suriano & Beverley-Burton, 1982 (Monogenea: Ancyrocephalidae) on the gills of the rare striated darter, Etheostoma striatulum Page & Braasch (Perciformes: Percidae), from the Duck River, Tennessee, USA.

The striated darter (Etheostoma striatulum Page & Braasch) is a rare fish species restricted to the Duck River system in Maury County, Tennessee, USA. In this paper we describe Aethycteron striatuli n. sp., a gill parasite from a genus that has specialised on darters as the parasites' preferred hosts. Aethycteron striatuli morphologically resembles A. malleus (Mueller, 1938), A. robisoni Cloutman & McAllister, 2017, A. chlorosomus (Harrises & Vickery, 1970) and A. micropercae Suriano & Beverley-Burton, 1982. It is distinguished from other species in that it is one of the smallest described parasites in this genus to date and possesses a small male copulatory organ with a distinct accessory piece. This is the first monogenean parasite reported from E. striatulum, a species that is currently under threat due to its restricted range and the potential for habitat loss. It is essential to expand our knowledge of the host and the pressures it faces in its limited habitat, including disease and parasite pressures, so that measures can be taken to preserve this vulnerable native species.