[Photoreactions of the littoral trematode Renicola thaidus (Trematoda: Renicolida)].

The behavioral response of Renicola thaidus cercariae (Renicolidae) to the light has been studied. The positive photo reaction was observed during the first hour of the cercariae free-living period (after shedding from the mollusc). Six hour old cercariae did not show any direct photo reaction. Temporal presence of the positive photo reaction promotes a wider spatial distribution of R. thaidus cercariae. This fact may increases a probability of successful finding and infection of the second intermediate host--bivalves such as the blue mussels. Besides, the more random distribution of infection in bivalve host populations is achieved. This circumstance increases a probability of infected bivalve to be eaten by the final hosts--seabirds.