Pseudohurleytrema yolandae n. sp., the first monorchiid trematode reported from the Triacanthidae (Tetraodontiformes).

Prior to the present study, species of the trematode family Monorchiidae Odhner, 1911 had been reported from four of the ten families of tetraodontiform fishes: the Balistidae, Monacanthidae, Ostraciidae and Tetraodontidae. Here we report the first monorchiid from the family Triacanthidae, Pseudohurleytrema yolandae n. sp. infecting Tripodichthys angustifrons (Hollard), from Moreton Bay, Queensland, Australia. The species conforms well to the morphological concept of the subfamily Hurleytrematinae Yamaguti, 1958, and the genus Pseudohurleytrema Yamaguti, 1954, in the possession of filamented eggs, a bipartite terminal organ, and a unipartite seminal vesicle. Relative to the other three recognised species of Pseudohurleytrema, the present species is distinctive in the size of the testis and eggs, position of the ovary, and the form of the vitellarium and excretory vesicle. We consider Pseudohurleytrema magnum Kaikabad & Bilqees in Bilqees, 1991 as a species inquirenda. Sequence data for the 28S ribosomal RNA gene and cox1 mitochondrial gene were generated for P. yolandae, providing the first molecular data for the genus. Phylogenetic analysis showed that P. yolandae does not form a clade with the other three hurleytrematine genera for which there are molecular data (Helicometroides Yamaguti, 1934, Hurleytrematoides Yamaguti, 1953 and Provitellus Dove & Cribb, 1998), forming a poorly-supported clade with Proctotrema addisoni Searle, Cutmore & Cribb, 2014 within the clade of the subfamily Monorchiinae Odhner, 1911. The four hurleytrematine genera resolved as four distinct clades, indicating that the current subfamilial classification requires comprehensive revision.