Description and life-cycle of three new species of Dingularis n.g. (Digena: Plagiorchiida), parasites of Australian freshwater turtles.

Dingularus n.g. is proposed to accommodate three new species, D. anfracticirrus, D. pearsoni and D. megapharynx, within the Plagiorchiida. Dingularus is closely related to the Plagiorchiidae, despite the unusual excretory systems of the three species. Adult worms were parasitic in the intestines of freshwater turtles, Chelodina expansa (D. pearsoni and D. megapharynx) and Emydura macquarii (D. anfracticirrus), and appeared to be host-specific. The three species had similar, three-host, aquatic life-cycles and each life-cycle was followed experimentally. The planorbid snail Glyptophysa gibbosa served as the first intermediate host for each species. Tadpoles of Limnodynastes peronii and snails G. gibbosa and Austropeplea lessoni served as second intermediate hosts. Dingularus spp. eggs were fully embryonated and infective when laid. They remained viable for 2-3 months in water but did not hatch until eaten by G. gibbosa. Miracidia were stimulated in the stomach of the snail host but did not hatch until eggs passed into the intestine. Hatching occurred in only the anterior fifth of the intestine. Hatched miracidia were not passed with the snail faeces. The pre-patent period in the snail differed in each species: D. anfracticirrus 42 days, D. pearsoni 23 days and D. megapharynx 32 days.