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The Indo-west Pacific is a marine bioregion stretching from the east coast of Africa to Hawaii, French Polynesia and Easter Island. An assessment of the literature from the region found reports of 2,582 trematode species infecting 1,485 fish species. Reports are concentrated in larger fishes, undoubtedly reflecting the tendency for larger hosts to be infected by more species of parasites as well as a collecting bias. Many hundreds of fish species, including many from families known to be rich in trematodes, have yet to be reported as hosts. Despite some areas (the Great Barrier Reef, Hawaii and the waters off China, India and Japan) receiving sustained attention, none can be considered to be comprehensively known. Several regions, most importantly in East Africa, French Polynesia and the Coral Triangle, are especially poorly known. The fauna of the Indo-west Pacific has been reported so unevenly that we consider it impossible to predict the true trematode richness for the region. We conclude that the greatest gap in our understanding is of the geographical distribution of species in the Indo-west Pacific. This is highlighted by the fact that 87% of trematodes in the region have been reported no more than five times. The reliable recognition of species is a major problem in this field; molecular approaches offer prospects for resolution of species identification but have been little adopted to date.

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This article was registered in the Official Register of Zoological Nomenclature (ZooBank) as C1C6A0B8-0716-4C0F-997B-7AF68C95B0B4. This article was published as an Online First article on the online publication date shown on this page. The article should be cited by using the doi number. This is the Version of Record.

Using novel molecular and morphological data we elucidated the life-cycle of Gorgocephalus yaaji Bray & Cribb, 2005 from off Lizard Island, on the northern Great Barrier Reef, Australia. ITS2 rDNA sequences generated for larval trematodes from the infected snail species Echinolittorina austrotrochoides Reid (Littorinidae) were identical to those from adult G. yaaji from the fish Kyphosus cinerascens (Forsskål) (Kyphosidae). Cercariae develop in rediae in E. austrotrochoides, emerge from the snail, encyst on algae as metacercariae, and are inferred to then be consumed by the herbivorous definitive fish host, K. cinerascens. In addition, we generated the first ITS2 rDNA sequences for a gorgocephalid previously reported from the littorind gastropod Austrolittorina unifasciata Gray. Although infections previously reported from A. unifasciata were the first larval gorgocephalids characterised, this study is the first to connect an intramolluscan infection to a sexual adult. In light of the new life-cycle information, a review of mollusc associations for the digenean superfamily Lepocreadioidea was performed, highlighting gaps in the knowledge and revealing patterns of host-parasite association. We find that distinct patterns of first intermediate host association are discernible for three lepocreadioid lineages: the Aephnidiogenidae Yamaguti, 1934, Gorgocephalidae Manter, 1966, and the Lepocreadiidae Odhner, 1905. However, the evolutionary origin for these patterns of host association remains unclear.