Denarycotyle gardneri n. gen., n. sp. (Monogenea: Monocotylidae: Euzetiinae), from the gills of Rhinoptera steindachneri (Rhinopteridae) from Acapulco, Guerrero, Mexico

Denarycotyle gardneri n. gen., n. sp. (Monogenea: Monocotylidae) is described from the gills of the stingray, Rhinoptera steindachneri (Myliobatidae), collected in marine waters off Acapulco, Guerrero, Mexico. The genus is assigned to Euzetiinae because it has a haptor with one central loculus, one additional loculus on either side of the central loculus and 10 peripheral loculi. However, the genus described herein can be distinguished from Euzetia, the only genus currently assigned to Euzetiinae, by the presence of two accessory structures on the dorsal surface of the haptor and hamuli with a sclerotized accessory piece on each hamulus. Specimens of D. gardneri n. gen., n. sp. were found on the gills of 4 of 18 individuals of R. steindachneri (22%) but were not present on Rhinobatos glaucostigma Jordan and Gilbert (1 individual), Urotrygon rogersi (Jordan and Starks) (2), Narcine entemador Jordan and Starks (3), Aetobatus narinari (Euphrasen) (1) or Dasyatis longa (Garman) (3). This is the third genus and the fourth species of a monogenean recorded from Rhinoptera and the second member of Euzetiinae from Mexico and from the neotropics. Keys to the subfamilies of Monocotylidae and to the species of Euzetiinae, as well as a hypothesis of phylogenetic relationships between Heterocotylinae, Decacotylinae, and Euzetiinae are provided.