On misidentification of metacercariae of Posthodiplostomum minimum (MacCallum, 1921) Dubois, 1936, in Nearctic minnows.

Posthodiplostomum minimum (MacCallum, 1921) Dubois, 1936 (Digenea, Diplostomidae) was described from adult worms from a great blue heron (Ardea herodias; Ardeidae) in New York. Metacercariae have been widely reported from diverse freshwater fishes, despite early experimental work and recent molecular data indicating exclusive infection of minnows (Leuciscidae) in North America. We compared the type specimens of P. minimum to adults taken from domestic chicks (Gallus gallus domesticus) fed metacercariae from fathead minnow (Pimephales promelas; Leuciscidae), as well as adults in naturally infected ardeid hosts. Sequences of cytochrome c oxidase I (CO1) showed these specimens were conspecific with worms from leuciscids and ardeids sampled across North America. However, adult morphology of the species with metacercariae in North American leuciscids differed markedly from the type specimens of P. minimum. Consequently, we resurrect and transfer to Posthodiplostomum Dubois, 1936, the earliest name for the lineage infecting leuciscids in North America: Posthodiplostomum vancleavei (Agersborg, 1926) n. comb. In North America, the four most likely junior synonyms of P. minimum are Posthodiplostomum aztlanensis González-García, López-Jiménez, Ortega-Olivares, Sereno-Uribe, Pérez-Ponce de León et García-Varela, 2024, Posthodiplostomum dawnsherryae Achatz, Von Holten, Pritchard et Keel, 2025, Posthodiplostomum nanum Dubois, 1937, and Posthodiplostomum seminolense Achatz, Von Holten, Pritchard et Keel, 2025. Sequences of CO1 indicate P. vancleavei n. comb. has been introduced in Japan and we discuss the high likelihood of its establishment in Europe. The complete rDNA operon and near-complete mitochondrial genome sequence of P. vancleavei show expected phylogenetic affiliation with Posthodiplostomum centrarchi Hoffman, 1958.