Twenty one of 29 species of snappers (Lutjanidae), examined for dactylogyrids (Monogenoidea) from the Red Sea, Persian Gulf, the Indo-west and eastern Pacific Ocean, the Gulf of Mexico, and Caribbean Sea were parasitized by 16 new and 11 previously described species of Euryhaliotrema: Euryhaliotrema adelpha sp. nov., Euryhaliotrema anecorhizion sp. nov., Euryhaliotrema cardinale sp. nov., Euryhaliotrema chrysotaeniae, Euryhaliotrema cognatus sp. nov., Euryhaliotrema cryptophallus sp. nov., Euryhaliotrema diplops sp. nov., Euryhaliotrema distinctum sp. nov., Euryhaliotrema fajeravilae sp. nov., Euryhaliotrema fastigatum, Euryhaliotrema fatuum sp. nov., Euryhaliotrema ferocis sp. nov., Euryhaliotrema hainanense, Euryhaliotrema longibaculum, Euryhaliotrema mehen comb. nov., Euryhaliotrema paracanthi, Euryhaliotrema paululum sp. nov., Euryhaliotrema perezponcei, Euryhaliotrema ramulum sp. nov., Euryhaliotrema seyi sp. nov., Euryhaliotrema simplicis sp. nov., Euryhaliotrema spirotubiforum, Euryhaliotrema tormocleithrum sp. nov., Euryhaliotrema torquecirrus, Euryhaliotrema tubocirrus, Euryhaliotrema xinyingense, and Euryhaliotrema youngi sp. nov. Six species of Euryhaliotrema, previously reported from lutjanid hosts, were not collected: Euryhaliotrema anguiformis comb. nov., Euryhaliotrema guangdongense, Euryhaliotrema johni, Euryhaliotrema lutiani, Euryhaliotrema lutjani, and Euryhaliotrema nanaoense comb. nov. The diagnosis of Euryhaliotrema was emended to include species having tandem or slightly overlapping gonads, a pretesticular germarium, a globose haptor with morphologically similar anchors and hooks, a coiled or meandering male copulatory organ, a dextral vaginal pore, and hooks with upright acute thumbs and slender shanks comprised of one subunit. A bulbous base of the MCO and presence of an accessory piece in the copulatory complex were no longer considered features defining the genus. As a result, Euryhaliotrematoides and Aliatrema were placed in subjective synonymy with Euryhaliotrema, and the following transfers were proposed: Euryhaliotrema annulocirrus comb. nov., Euryhaliotrema aspistis comb. nov., Euryhaliotrema berenguelae comb. nov., Euryhaliotrema cribbi comb. nov., Euryhaliotrema grandis comb. nov., Euryhaliotrema mehen comb. nov., Euryhaliotrema microphallus comb. nov., Euryhaliotrema pirulum comb. nov., and Euryhaliotrema triangulovagina comb. nov. In addition, the following new combinations were proposed based on the revised diagnosis of the genus: Euryhaliotrema anguiformis comb. nov., Euryhaliotrema eukurodai comb. nov., Euryhaliotrema kurodai comb. nov., Euryhaliotrema monoporosum comb. nov., and Euryhaliotrema nanaoense comb. nov. The dactylogyrids, Protancyrocephalus rangusi (from a lutjanid host) and Daitreosoma chaetodontis (from a chaetodontid host), were considered species inquirendae. Haliotrematoides tukerhamatus comb. nov. is considered the senior subjective synonym of Haliotrematoides nagabinae. New host records for some previously described species of Euryhaliotrema from lutjanid and chaetodontid hosts were reported.

The generic diagnosis of Aristocleidus Mueller, 1936 is emended based on a collection of 2 species of the genus from the gills of the Peruvian mojarra, Diapterus peruvianus (Gerreidae), from a lagoon along the Pacific Coast of Mexico. The genus is characterized in part by species having a deeply incised base of the ventral anchor with the tip of the superficial root conspicuously directed toward that of the deep root. Aristocleidus hastatus Mueller, 1936 is redescribed and Aristocleidus lamothei n. sp. is described from D. peruvianus from the Tres Palos Lagoon, Guerrero State, Mexico. The finding of A. hastatus on D. peruvianus in Mexico represents new host and locality records for the species.

Se completa la descripción de Aristocleidus Mueller, 1936 con base en 2 ejemplares recolectados de las branquias de la mojarra peruana, Diapterus peruvianus (Gerreidae), de una laguna situada en la costa del Pacífico de México. El género se caracteriza por tener la base del macrogancho ventral profundamente hundida, con la punta de la raíz superfcial dirigida marcadamente hacia la de la raíz profunda. Se redescribe Aristocleidus hastatus Mueller, 1936 y se describe Aristocleidus lamothei n. sp. de D. peruvianus de la laguna de Tres Palos, Guerrero, México. El hallazgo de A. hastatus en D. peruvianus representa un nuevo registro de hospedero y localidad.

Sumário Cinco novas espécies de Monogenoidea (Dactylogyridae: Ancyrocephalinae) foram descritas das brânquias de peixes de água doce da América do Sul: Jainus amazonensis, n. sp., Tereancistrum kerri, n. gen., n. sp., e Trinibaculum braziliensis, n. gen., n. sp. todas da matrinchã, Brycon melanopterus (Cope) do lago Januacá perto a Manaus, Amazonas, Brasil. Também Tereancistrum omatus, n. sp. de Prochilodus reticulatus Steindachner do rio Caucá, Juanchito, Cali, Valle, Colômbia, e T. parvus, n. sp. do aracu, Leporinus fasciatus (Bloch) da Amazônia. Dois novos gêneros foram propostos. Tereancistrum, n. gen. foi caracterizado por ter escleritos espatulados como acessórios associados com os ganchos grandes ventrais. Trinibaculum, n. gen. foi estabelecido para as espécies com uma única barra ventral, duas barras dorsais bem separadas, uma vagina dextroventral, os ramos intestinais unidos e gônadas intercecais.

Abstract Five new species of Monogenoidea (Dactylogyridae: Ancyrocephalinae) are described from the gills of freshwater fishes of South America: Jainus amazonensis sp. n., Tereancistrum kerri gen. et sp. n., and Trlnibaculum braziliensis gen. et sp. n. (all) from Brycon melanopterus (Cope), Januacá Lake near Manaus, Amazonas, Brasil; Tereancistrum ornatus sp. n. from Prochilodus reticulatus Steindachner, Rio Cauca, Juanchito, Cali, Valle, Colombia; and T. parvus sp. n. from Leporinus fasciatus (Bloch), Amazon River Basin. Two new genera are proposed. Tereancistrum gen. n. is characterized by having spathulate acessory anchor sclerites associated with the ventral anchors. Trinibaculum gen. n. is proposed for species with a single ventral bar, two widely separated dorsal bars, a dextroventral vagina, confluent intestinal crura, and intercecal gonads.