Helicometra Odhner, 1902 (Digenea: Opecoelidae) in Australian waters: problems of species identification and a description of H. sprenti n. sp.

Helicometra Odhner, 1902 is reported from temperate Australian marine teleosts in which it appears to be rare. Of 285 species of fishes from 84 families examined, only 10 species from 9 families were infected. One infection, that in Platycephalus speculator caught from off the coast of Western Australia, is highly distinctive and the name Helicometra sprenti n. sp. is proposed for this species. The other infections were from members of the Antennariidae, Apogonidae, Kyphosidae, Labridae, Paralichthyidae, Pinguipedidae, Scorpaenidae and Sparidae, all from off southern Queensland and New South Wales. There is no evidence that infections are common in any of these hosts, which have little relationship to each other. Measurements and figures are presented for representatives from all the host species. Only minor variation was found in features such as body dimensions and the extent of the vitelline follicles, and it is concluded that the specimens probably represent a single species with a very low host-specificity. We suspect that the general scarcity of the worm is consistent with the presence of only one species, although the possibility that a species-complex is present cannot be ruled out. The specimens are broadly consistent with H. fasciata (Rudolphi, 1819), a species first described from Europe, and they are tentatively identified as this species, although it seems likely that ultimately they will prove to represent a different taxon. Determination of the ultimate identity of this form will require the application of molecular and life-cycle studies of worms from different hosts and localities.