Unveiling the diversity and phylogenetic framework of Pseudomurraytrematidae (Monopisthocotyla: Dactylogyridea), ectoparasites of catostomid fishes (Cypriniformes)

An extensive survey of North American catostomid fishes yielded insights into the diversity, host specificity and phylogenetic relationships of monopisthocotylans belonging to Pseudomurraytrematidae. Parasites were recorded from 14 of 16 host species surveyed. In total, 22 species of <i>Anonchohaptor, Icelanonchohaptor</i> and <i>Pseudomurraytrema</i> were collected, including 7 new species. Most species were recovered from gills, whereas two <i>Icelanonchohaptor</i> species were found on fins. Phylogenetic analyses based on 28S rDNA support the monophyly of Pseudomurraytrematidae and its sister relationship to Diplectanidae. Within the family, <i>Pseudomurraytrema asiaticum</i> - a parasite of the East Asian fish <i>Myxocyprinus asiaticus</i> - was recovered as sister to the clade of Nearctic pseudomurraytrematids, a placement that may reflect geographic and host-associated separation. The remaining <i>Pseudomurraytrema</i> species parasitize North American Catostominae and form a well-supported clade sister to the clade comprising species of <i>Anonchohaptor</i> and <i>Icelanonchohaptor</i>, primarily associated with Ictiobinae. Under this topology, <i>Pseudomurraytrema</i>, as currently circumscribed, may be paraphyletic. Relationships between morphologically similar species of <i>Anonchohaptor</i> and <i>Icelanonchohaptor</i> remain unresolved: in the 28S tree, <i>Anonchohaptor</i> is paraphyletic (with <i>Icelanonchohaptor</i> nested within it), whereas the concatenated 18S-ITS1-28S analyses recover a single clade with <i>Icelanonchohaptor</i> (2 spp.) sister to the remaining species of <i>Anonchohaptor</i>. The parasite phylogeny broadly reflects host relationships, though several incongruences point to historical host switching. Morphological data also support the monophyly of Pseudomurraytrematidae via a synapomorphic male copulatory organ (U-shaped copulatory tube with a submedial spine, 3-ramus accessory piece), indicating structural conservatism within this family.