The life cycle of Asymphylodora tincae (Modeer 1790) (Trematoda: Monorchiidae): a unique development in monorchiid trematodes.

A study on the life cycle of the trematode Asymphylodora tincae (Modeer 1790) (family Monorchiidae), carried out under both natural and laboratory conditions, revealed as its most remarkable characteristics the absence of a metacercarial stage. The definitive host, the tench [Tinca tinca (L.)], became directly infected after the ingestion of snails harbouring rediae with mature cercariae. With the exception of the sporocyst, all developmental stages from both naturally and experimentally infected pulmonate snails as well as adults from experimental fish hosts were described and illustrated, including the surface morphology of the cercariae, studied by scanning electron microscopy. Confusion in the identification of larval stages from pulmonate snails and the prosobranchiate genus Bithynia, hitherto identified as A. tincae by other authors, are briefly discussed with regard to the present results.