This thesis explores the taxonomy, systematics and phylogenetic status of the family Faustulidae from corallivorous fishes in the Tropical Indo-west Pacific (TIWP). The main study is based on the parasitological examination of 2,901 individual coral reef fishes from six major TIWP localities:Reef, Western Australia; Palau; Lizard Island, Swain Reefs complex and Heron Island (all Queensland); and French Polynesia. Faustulidae are mainly parasites of the intestine of marine teleosts and are characterised by a spiny tegument, a canalicular seminal receptacle and a posterior opening Laurer's canal. Of the 12 genera that belong to this family, the largest, and the main focus of this study, is Paradiscogaster Yamaguti, 1934. Before this study, Paradiscogaster comprised 24 species distributed in the Indo-west Pacific and infecting 13 families of fish. Of these, corallivorous fishes from the family Chaetodontidae had the largest number of Paradiscogaster species, followed by fishes, with a diverse diet, from Monacanthidae and Ostraciidae. The results from this study are structured first as three taxonomic chapters describing new species from this genus; I described and published six new Paradiscogaster species from Chaetodontidae and Ephippidae, and a further five new species not yet published: two new species corresponding to the v Publications during candidature Peer-reviewed papers: Diaz, P. E., Bray, R., Cutmore, S. C., Ward, S., & Cribb, T. H. (2015). A complex of species relating to Paradiscogaster glebulae (Digenea: Faustulidae) in chaetodontid fishes (Teleostei: