THE ULTRASTRUCTURE OF THE NERVOUS SYSTEM IN THE TREMATODE SANGUINICOLA PLEHNAE (DIGENEA, SANGUINICOLIDAE)

А detailed ultrastructural study was performed for the nervous system of Sanguinicola plehnae found in the Esox lucius branchial arteries. Its nervous system consists of a neuropil, a dense collection of axons surrounded by nerve cell bodies located around the neuropil. Four types of neurovesicles were found in S. plehnae neurons: small clear vesicles, dense-core vesicles, large dense vesicles and large lucent vesicles. Large neurons in S. plehnae contain one type of vesicles (large dense vesicles), but most perikaryons of peripheral neurons contain both small clear vesicles and densecore vesicles. In S. plehnae most axon presynaptic terminals contain small, clear, and dense vesicles; axons with three types of vesicles are also present. No glia-like structures were detected in the nervous system at the ultrastructural level. However, single muscle perikaryons and muscle fibers were identified in the neuropil. In S. plehnae, which lacks suckers and has miniature gut, a simple, uniformly developed nervous system was found. Such a structure can be considered as an apomorphic character for Sanguinicola species.