Studies on the life-cycle of the digenetic trematode Rhipidocotyle campanula (Dujardin, 1845) (Gasterostomata: bucephalidae) with particular reference to the larval stages
The life-cycle of Rhipidocotyle campanula (Dujardin, 1845) has been experimentally demonstrated and the species identity confirmed. Sporocysts were recovered from digestive glands of the freshwater-mussel Anodonta anatina, and in heavily infected 'hosts from the reproductive, system. Both cercariae and glochidia are released simultaneously in mussels where the reproductive system is partly invaded by sporocyst tubules. The development of the cercariae in the sporocyst tubules has been studied briefly fusing histological and histochemical methods. The liberation of cercariae varied- between >1000/mussel/day to none, and is intermittent. Behaviour of the cercariae including swimming, response to light and gravity, survival and entry, into the secondary host, is described. The morphology of the cercaria has been studied in detail using electron microscopy, histochemistry and histological methods and its significance analysed in relation to free-living existence. This is the first attempt to study the cercaria of R. campanula in any detail. Cercariae enter the secondary host passively and encyst in the subcutaneous fatty tissue beneath the lining of the pharynx, and in some cases in the gill arches. This is the only species of bucephalids where cercariae enter the secondary host passively. Encysted metacercariae attain maximum development after 5-6 weeks and survive nearly 200 days, but spontaneous excystation takes place only in cysts 80-90 days old. Adult flukes were recovered from the posterior intestine and rectum of the perch (Perca fluviatilis) six weeks after feeding fully developed metacercariae. Spermatogenesis and oogenesis were studied in the adults until egg formation. Miracidial development could not be observed. External morphology using SEM of cercaria, metacercaria and adult has been studied and compared. This is the first report of SEM study of these stages of R. campanula. A brief review of the literature is given and the problems of systematics and taxonomy of the family Bucephalidae the taxonomic position of R. campanula are discussed.Tabular summaries are given for the previous life-cycle studies of bucephalids, synopses of bucephalid trematodes and all previous reports of bucephalid cercariae.