Revision of monogeneans parasitising Lythrurus (Cypriniformes: Leuciscidae) in eastern U.S.A., with description of Dactylogyrus lythruri sp. n. and new records of Dactylogyrus crucis Rogers, 1967 (Monogenoidea: Dactylogyridae).

A revisionary study revealed two species of monogeneans, Dactylogyrus crucis Rogers, 1967 and Dactylogyrus lythruri sp. n., parasitising Lythrurus Jordan (formerly a subgenus of Notropis Rafinesque, 1818). New records and updated taxonomy of seven of 12 known minnows of the genus of Lythrurus are provided for D. crucis. A record of Dactylogyrus attenuatus Mizelle et Klucka, 1953 (syn. Dactylogyrus umbratilus [Kimpel, 1939], nomen nudum) on Lythrurus umbratilis (Girard) is referrable to D. crucis. Dactylogyrus lythruri is described from eight species of Lythrurus. It most closely resembles Dactylogyrus beckeri Cloutman, 1987, but is distinguished by having a smaller base of the male copulatory organ (MCO) and lacking a ventral enlargement of the distal end of the basal process. Previous reports of Dactylogyrus banghami Mizelle et Donahue, 1944 and Dactylogyrus cf. beckeri Cloutman, 1987 from Lythrurus atrapiculus (Snelson) and Lythrurus bellus (Hay) from Alabama, and Dactylogyrus confusus Mueller, 1938 from L. umbratilis in Illinois are herein relegated to D. lythruri. Four species of Lythrurus appeared not to be infected with Dactylogyrus.

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.