Expansion of the concept of the Opistholebetinae Fukui, 1929 (Digenea: Opecoelidae Ozaki, 1925), with Magnaosimum brooksae n. g., n. sp. from Tripodichthys angustifrons (Hollard) (Tetraodontiformes: Triacanthidae) in Moreton Bay, Australia.

The Opecoelidae Ozaki, 1925, the largest trematode family, currently lacks an adequate subfamilial organisation. In particular, recent analyses have shown that the sequenced representatives of the Opistholebetinae Fukui, 1929 are nested among taxa currently recognised in the Plagioporinae Manter, 1947, which itself is polyphyletic. The concept of the Opistholebetinae persists because its 25 or so species are united by a distinctive morphology and a narrow host range; species are known only from tetraodontiform fishes, specifically of the Tetraodontidae and Diodontidae, and possess a muscular post-oral ring, unusual pigmented granules throughout the body and a ventral sucker positioned more posteriorly than is typical for other opecoelids. Here we report on Magnaosimum brooksae n. g., n. sp. from a tetraodontiform, Tripodichthys angustifrons (Hollard) (Triacanthidae), collected in Moreton Bay, Australia. The new species has a longer forebody than hindbody, but lacks a post-oral ring and pigmented granules. It resolves to the plagioporine clade containing the Opistholebetinae, but does not form a monophyletic grouping with those taxa. We propose to expand the concept of the Opistholebetinae to include Magnaosimum, as well as Gaevskajatrema Gibson & Bray, 1982, Macvicaria Gibson & Bray, 1982, Pachycreadium Manter, 1954, Peracreadium Nicoll, 1909, Pinguitrema Siddiqi & Cable, 1960, Propycnadenoides Fishcthal & Kuntz, 1964, Pseudopycnadena Saad-Fares & Maillard, 1986, Pycnadena Linton, 1911 and Pycnadenoides Yamaguti, 1938.