The genus Rhadinorhynchus (Acanthocephala: Rhadinorhynchidae) from marine fish in Australia with the description of four new species.

Species of Rhadinorhynchus, collected from Australian waters were examined. Specimens of Rhadinorhynchus from Scorpis aequipinnis, Girella tricuspidata, Johnius australis and Grammatobothus polyophthalmus could not be identified further. New host and locality records are reported for R. bicircumspinus found in Trachurus declivis and Rexea solandri from the east coast of Tasmania; R. carangis found in Trachinotus bailonii and T. copperingi from Queensland and Western Australian coasts; R. polynemi from Queensland; R. seriolae found in Seriola lalandi from the east coast of Australia. An immature female specimen of R. johnstoni provided no additional data on the species. Rhadinorhynchus biformis sp. nov., described from Pelates quadrilineatus and a trumpeter from Moreton Bay, Queensland differs from all its congeners in the pattern of the trunk spines, a single field of numerous small spines ventro-laterally, overlapping with irregular rows and circles of larger spines extending posteriorly. Rhadinorhynchus pichelinae sp. nov. described from Upeneichthys vlamingi from Point Peron, Western Australia differs from all its congeners in having proboscis armature of 10 longitudinal rows of 24-28, usually 26-27 hooks up to 87 long and a single field of 21-24 irregular circles of spines on the anterior trunk, with the posterior circles incomplete dorsally. Rhadinorhynchus polydactyli sp. nov. described from Polydactylus sp. from Moreton Bay is differentiated from all congenerics by the elongated neck of the females and having a proboscis armature of up to 34 hooks in 10 longitudinal rows. Rhadinorhynchus pomatomi sp. nov. found in Pomotomus saltrix differs from its most similar congeners, those without dorsal trunk spines, in having a proboscis armature of 12-15 rows of 20-22 hooks up to 73.5-80.5 long. Rhadinorhynchus bicircumspinus, R. biformis, R. pichelinae, R. polydactyli and R. pomatomi are known only from Australian waters while R. carangis and R. seriolae are also known from Japanese waters, R. johnstoni from the western Pacific and R. polynemi from the Indian coast.