Genetic characterisation of cercarial stages of Choanocotyle Jue Sue and Platt, 1998 (Digenea Choanocotylidae) in a native Australian freshwater snail, Isidorella hainesii (Tryon)

Isidorella hainesii (Tryon, 1866) is a native freshwater snail, belonging to the family Planorbidae, commonly found on aquatic vegetation in south eastern parts of Australia. In the present study, we report natural infection with a species of Choanocotyle Jue Sue and Platt, 1998 (Digenea: Choanocotylidae) parasite in inland Australia for the first time, followed by characterisation of the parasite using both morphological and molecular approaches. Snails (n = 150) were collected from recently drained, natural ponds at a local fish farm located in the Riverina region, New South Wales, Australia. Parasites were subjected to preliminary morphological examination followed by DNA extraction to obtain their ITS-2, 18S and 28S sequences. Based on their sequence data and phylogenetic analyses they were identified as Choanocotyle hobbsi Platt and Tkach, 2003, which has only previously been described from Chelodina oblonga Gray, 1841 (snake-necked turtle) in Western Australia. Previous researchers suggested that in Australia, C. oblonga and its parasite fauna are separated from their eastern counterparts due to formation of impenetrable waterless desert in the country during the late Cretaceous. Our study extends the distribution of Choanocotyle hobbsi from Western Australia to the Murray Darling Basin in New South Wales, however, the definitive host remains unknown in New South Wales.