ИСТИНА

Free-living trematode (Digenea) larvae, cercariae, are non-feeding minute organisms whose only role is to find and infect the next host, a step which is crucial for the survival of the parasite species. Cercariae often demonstrate fast sensory-motor reactions to different stimuli and have provisory organ for locomotion – the tail. The data on morphology of the nervous system in the tail of cercaria is incomplete and often contradictory. MATERIAL AND METHODS. Samples of marine cercariae Cryptocotyle lingua from periwinkles Littorina littorea were collected in the littoral zone of Chupa Bay, White Sea at the Marine Biological Station of the Zoological Institute, Russian Academy of Science, Russia. Series of ultrathin longitudinal and cross sections were studied by transmission electron microscopy. RESULTS. For the first time we depicted the morphology of the nervous system in the tail of cercaria in cellular resolution. We characterized one unpaired and ten pairs of the neurons organized in the simple circuit. Details of neurons morphology, neuron to muscles and neuron to neuron connections could suggest different functional roles of the cells in the network. The data is discussed in the contest of CPG and limited data on electrophysiology and immunocytochemistry of the species studied.