Morphological and molecular data reveal a new genus and species from the family Transvenidae (Echinorhynchida: Palaeacanthocephala) from Bahía de Todos los Santos, Northeast Pacific, Mexico

Echinorhynchids are a group of globally distributed acanthocephalan parasites mainly of freshwater, brackish and marine fishes and occasionally, reptiles and amphibians. During several parasitology surveys in the Gulf of Mexico and Northeast Pacific, Mexico, acanthocephalans were recovered from two marine fish species. The specimens from the Gulf of Mexico were identified as Caballerorhynchus lamothei (Cavisomidae), a typical parasite of the striped mojarra, whereas adult acanthocephalans from the Northeast Pacific, Mexico, from the Garibaldi fish exhibited morphological characteristics belonging to the family Transvenidae. Sequences from the small (SSU) and large (LSU) subunits of ribosomal DNA and cytochrome c oxidase subunit 1 (cox 1) of mitochondrial DNA were obtained for both species. The new sequences were aligned with other sequences available in the GenBank dataset from Echinorhynchida. Phylogenetic trees inferred with the combined (SSU + LSU), concatenated (SSU + LSU+ cox 1), and cox 1 datasets consistently placed the two species into two independent lineages. The species C. lamothei from Cavisomidae was placed in a clade together with members from Spinulacorpidae, Rhadinorhynchidae and Transvenidae, suggesting that Cavisomidae is paraphyletic. The unidentified specimens were nested inside a clade formed by members of Transvenidae. Morphologically, the new samples presented a combination of unique diagnostic traits, which was not observed in other members of the Transvenidae family. Therefore, the genus Darwinorhynchus was created to accommodate a new species named herein as Darwinorhynchus bajacaliforniaensis n. gen., n. sp. The current record from a transvenid acanthocephalan expands its distribution range to the northern Pacific in the Americas, Indian Ocean and Arabian Gulf.