A new genus, Choanocotyle, is proposed to include two plagiorchiidan species. Choanocotyle elegans n. sp. is described from the small intestine of the freshwater turtles Chelodina expansa and Emydura macquarii. Choanocotyle nematoides n. sp. is described from the large intestine of E. macquarri. Descriptions are given of the adult, egg and miracidium, cercaria and metacercaria of each species. The two species have similar three-host aquatic life-cycles. A planorbid snail, Glyptophysa gibbosa, served as first intermediate host for both species in the laboratory. Isidorella newcombi was found naturally infected with C. elegans. Eggs were fully embryonated and infective when laid, but did not hatch until eaten by G. gibbosa. The intramolluscan prepatent period was 50 days for C. elegans and 35 days for C. nematoides. Metacercariae of C. elegans were recovered from experimentally infected snails ( G. gibbosa), tadpoles ( Limnodynastes peronii) and naturally infected crayfish ( Cherax sp.), while metacercariae of C. nematoides developed preferentially in the vertebral cartilage of L. peronii, but were also recovered from experimentally infected G. gibbosa, and field-collected leeches, Glossiphonia sp. Cercarial behaviour of each species is outlined briefly and observations are given on the host-parasite relationships of the metacercariae of each species. The disposition of Choanocotyle within the Plagiorchiida is discussed and it is concluded that it would be best placed in a new family, the Choanocotylidae.