Four new monorchiids from the golden trevally, Gnathanodon speciosus (Forsskål) (Perciformes: Carangidae), in Moreton Bay, Australia.

Four new monorchiid trematodes are reported from Moreton Bay, Australia; three new species of Provitellus Dove & Cribb, 1998 and one species of Ovipusillus Dove & Cribb, 1998, are described from Gnathanodon speciosus (Forsskål) (Carangidae), the golden trevally. Provitellus chaometra n. sp., Provitellus infrequens n. sp. and Provitellus infibrova n. sp. differ significantly from the only other species of this genus, Provitellus turrum Dove & Cribb, 1998, in the structure of the eggs, vitelline follicles and terminal organ. The four species are united, however, in the possession of short caeca and a long genital atrium, a combination not reported previously. Ovipusillus geminus n. sp. strongly resembles its only congener, Ovipusillus mayu Dove & Cribb, 1998, but differs in the morphology of the diverticulum in the cirrus-sac and the shape of the pharynx. Complete ITS2 and partial 28S rDNA sequence data were generated for all four species, as well as for two known species of Hurleytrematoides Yamaguti, 1953, Hurleytrematoides galzini McNamara & Cribb, 2011 and Hurleytrematoides loi McNamara & Cribb, 2011. These sequences were analysed with those for other monorchiids available on GenBank, and phylogenetic analyses showed that the four species of Provitellus and two species of Ovipusillus each form strongly supported clades. As with previous monorchiid phylogenetic studies, however, the overall resolution of the phylogeny of the Monorchiidae is poor.