| Summary: | The monotypic genus <i>Deraiotrema</i> Machida, 1982 has only been reported once, from the orbicular batfish <i>Platax orbicularis</i> (Forsskål) in the waters around Palau in Micronesia (Machida, 1982). It has a body-shape similar to other lepocreadiids from batfishes, such as species of <i>Bianium</i> Stunkard, 1930 and <i>Diploproctodaeum</i> La Rue, 1926, but differs in having multiple testes in ventral and dorsal layers. Here we report <i>Deraiotrema platacis</i> Machida, 1982 for just the second time, infecting the dusky batfish <i>Platax pinnatus</i> (Linnaeus) from the waters off Lizard Island on the northern Great Barrier Reef. We present a molecular phylogenetic analysis of the position of this genus inferred from 28S rDNA sequences. Surprisingly, we find the species most closely related to <i>Echeneidocoelium indicum</i> despite the infection of completely unrelated hosts and the presence of two characters (lateral fold in the forebody and multiple testes) that are found elsewhere in the Lepocreadiidae. We conclude that homoplasy within the Lepocreadiidae is extensive and that morphology-based prediction of relationships has little prospect of success.
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