Description and life-cycle of Thrinascotrema brisbanica n. g., n. sp (Digenea : Plagiorchiida), a parasite of the freshwater turtle Elseya latisternum from Australia, and the erection of the family Thrinascotrematidae

A new genus and species, Thrinascotrema brisbanica, is proposed to accommod ate a plagiorchiidan trematode parasitic in the stomach of the freshwater t urtle Elseya latisternum. The distinctive taxonomic features of the parasit e are the shape and extent of the excretory bladder, and the stenostomate a rrangement of the excretory collecting ducts in the adult, cercaria and met acercaria together with a cercarial protonephridial formula of 2(12+12+12)(12+12+12). The life-cycle is three- host and aquatic. The pulmonate snail Glyptophysa gibbosa served as both a first and second intermediate host and tadpoles of Limnodynastes peronii, Adelotus brevis and Bufo marinus, and t he snail Austropeplea lessoni also served as second intermediate hosts. Egg s were fully embryonated and infective when laid, but did not hatch until e aten by the snail. Cercariae first emerged 55 days after infection at 24-28 degrees C. They were sluggish swimmers and survived for about 48 hr. They attached firmly to the skin of snails and tadpoles on contact and began to penetrate the skin after a short exploratory migration. Metacercariae survi ved in snails and tadpoles for at least 3 months. It is concluded that Thri nascotrema is best placed within a new family, the Thrinascotrematidae (Dig enea: Plagiorchiida), based on the unusual morphology of the excretory syst em.