Isorchis cannonin. sp. (Digenea: Atractotrematidae) from Great Barrier Reef rabbitfishes and the molecular elucidation of its life cycle

Abstract

AbstractWe describeIsorchis cannonin. sp. from the rabbitfishesSiganus fuscescens(Houttuyn) andSiganus lineatus(Valenciennes) (Siganidae) collected off Heron Island, southern Great Barrier Reef, Australia and, using molecular data, demonstrate that ‘Cercariae queenslandaeII’ of Cannon (1978) from the gastropodClypeomorus batillariaeformisHabe & Kosuge (Cerithiidae) is the larval form of this new species. The cercariae ofI.cannonin. sp. develop in rediae, encyst in the environment after emergence, and are inferred to then be consumed by grazing rabbitfish. Additionally, we provide a new report ofIsorchis curraniAndres, Pulis & Overstreet, 2016 from the type host,Selenotoca multifasciata(Richardson) (Scatophagidae) collected in Moreton Bay, south-east Queensland, Australia, greatly expanding the known geographical range of this species. Molecular sequence data (ITS1, ITS2 and 28S rDNA) generated forI.cannonin. sp. and the new specimens ofI.currani, confirm the identification ofI.curraniand demonstrate a distinct genotype forI.cannonin. sp. relative to other species ofIsorchisDurio & Manter, 1969, for which molecular data are available.Isorchis cannonin. sp. is morphologically distinct from all other species in the genus, and is further distinguished by utilizing species of Siganidae as definitive hosts, rather than species of Chanidae or Scatophagidae. Because haploporid and atractotrematid cercariae have well-developed reproductive organs, we find cercariae of these closely related families morphologically distinguishable in the same way as adult trematodes: atractotrematids have two symmetrical testes and haploporids have a single testis or, rarely, two tandem or oblique testes.