Geminate Parasite Species: Two New <i>Gyrodactylus</i> (Platyhelminthes, Monogenea) Infecting <i>Dormitator</i> spp. (Gobiiformes, Eleotridae) in the Pacific and Atlantic Coasts of Mexico Are Twin Lineages

ABSTRACT In this study, we describe two species of Gyrodactylus that parasitize fat sleeper fish on the coasts of Mexico: Gyrodactylus maculatus sp. n. infecting Dormitator maculatus in the Gulf of Mexico, Atlantic Ocean, and Gyrodactylus latifrons sp. n. infecting Dormitator latifrons along the Pacific coast. We used morphological and molecular data (ITS rDNA, cox2 mtDNA, 18S rDNA, and 28S rDNA) to erect and characterise the new species. Three species delimitation methods (Automatic Barcode Gap Discovery, Assemble Species by Automatic Partitioning, and Multispecies Coalescent Model) and phylogenetic analyses (Maximum Likelihood and Bayesian Inference) supported the recognition of the new species, which were shown to be geminate species. The occurrence of twin lineages of parasites on geminate host species estimated to have diverged ca . 0.4–5.1 million years ago, following the closure of the Central American Isthmus suggests that this vicariant event also resulted in the simultaneous evolution of geminate monogenean species. The use of four different molecular markers also enabled us to contribute to the ongoing discussion on the classification and phylogeny of the family Gyrodactylidae, by supporting previous findings suggesting that the genus Gyrodactylus is paraphyletic, and emphasises the importance of integrating both genetic and morphological data to develop a comprehensive classification system for this complex group of parasites.