The natural first intermediate host of Paragonimus siamensis (Miyazaki and Wykoff, 1965) in Thailand.

The first intermediate host of six-known the Paraf?onimus species in Thailand had not been found until the Filopaludina (Siamopaludina) martensi martensi snail was discovered to maintain the cercariae of a Parawmimus species. An extensive study examined cercaria! development through to adult worms by infecting 3 genera of 7 crab species with penetration of cercariae and feeding of snails contain­ ing such cercariae. These crabs provided many metacercariae which were fed to cats and bandicoots. The animals gave many Paraf?onimus adult worms which were characterized as Paraf?onimus siamensis by the following criteria: 6-lobed ovary and cuticular spines in groups. It is concluded that the Filopaludina martensi martensi snail is a susceptable natura/first intermediate host of P. siamensi.1·. Second intermediate hosts Somanniathelphusa brandti, S. sexpunctatum and S. banf?kokensis were experimentally infected; prior to this study only S. f?ermaini and S. duf?asti had ever been naturally infected with metacercariae of this species.