Ultrastructural peculiarities of interneuronal and neuromuscular relations in the trunkal part of the intraepidermal nervous system of Nerilla Sp. (Archiannelida)

This study deals with ultrastructural analysis of interneuronal and neuromuscular relations in a representative of archiannelid Nerilla sp. with primitive intraepidermal type of the nervous system. A particular attention has been paid to the area of ventral ciliate groove and the associated site of epidermis. In the ciliate groove, sensory and motor cilia are revealed and described. Sites of axonal terminals of the sensory cells supplied with cilia are noted in the epidermal nerve plexus. Epidermal-muscular cells and nerve terminals on them are revealed. Various interneuronal contact variants both of non-synaptic and of typically synaptic types are described. An attention is drawn to the rare presence of contacts of the gap junction type among interneuronal contacts in Nerilla sp. In sufficiently differentiated synapses of the chemical type, phenomena of exocytosis are described. There are shown specific features of innervation of longitudinal (somatic) musculature of the neril-lid body, including input of synaptic vesicles into the basal lamina substance and their translocation into the depth of the muscular layer.