Ligictaluridus michaelalicea n. sp. (Monogenea: Dactylogyridae) from flathead catfish (Pylodictis olivaris) in the upper Mississippi River, including remarks on taxonomy influencing monogenean treatment regulation in the United States.

Ligictaluridus michaelalicea n. sp. (Monogenea: Dactylogyridae, Ancyrocephalinae) is described from the gills of Pylodictis olivaris (Siluriformes: Ictaluridae) from Wisconsin and Iowa portions of the upper Mississippi River. Diagnostic features include a relatively large, strongly curved tubular cirrus with minor terminal flare; an accessory piece with a prominent basal lobe and a simple, thick terminal limb featuring a thin lateral flange and blunt distal tip devoid of recurved hooks. The sinistral vagina, two prostatic reservoirs, and a terminal seminal vesicle of the vas deferens are prominent. The anchors, ventral and dorsal bars, and hooks are similar in overall form to those of other members of the genus. The description includes sequence data for the 18S rRNA gene, which aligned most closely with species of ancyrocephaline monogeneans, with the highest similarity being with Ligictaluridus pricei (Mueller, 1936). Other monogenean species identified from the flathead catfish examined included L. pricei and Ligictaluridus mirabilis (Mueller, 1937). L. michaelalicea n. sp. is the fourth species to be described from P. olivaris within its natural range in central and eastern North America. Implications resulting from taxonomic name changes, including species of Ligictaluridus, and United States Food and Drug Administration treatment regulations are discussed. An updated key to species of the genus Ligictaluridus is presented.