Parachrisomon debonoae n. sp. (Digenea: Monorchiidae), a new species with significant intraspecific morphological variation infecting Mullidae (Mulliformes) from the eastern and western coasts of Australia.

We report trematodes conforming to the generic concept of Parachrisomon Madhavi, 2008, infecting multiple species of goatfishes (Mullidae) from Moreton Bay (south-eastern Queensland) and off Lizard Island (northern Great Barrier Reef) on the eastern coast of Australia, and from Ningaloo Reef on the western coast. Initial morphological analyses suggested the possible presence of multiple species; however, no morphological distinctions proved consistent. Molecular analyses demonstrate a distinction between western and eastern Australian samples, especially in mt cox1 sequence data, but the differences are interpreted as intraspecific geographical variation. Specimens from all localities share a bipartite terminal organ with an irregularly shaped and lobed anterior part; the other eight species of Parachrisomon are reported with unspecialised, bipartite terminal organs. We recognise the specimens as representing a new species, Parachrisomon debonoae n. sp., that exhibits significant intraspecific morphological variation, especially in body size, pharynx size, and shape and size of the ovary and testis. Additionally, we report novel molecular data for Parachrisomon delicatus (Manter & Pritchard, 1961) Madhavi, 2008.