Cellular organization of the common nerve plexus of the body wall of the <Emphasis Type="Italic">Nephthys ciliata</Emphasis> (polychaeta) in connection with problem of relative morphofunctional autonomization of the peripheral part of the central nervous system of annelids

The study deals with neurohistological analysis of the common nerve plexus of the body wall of the polychaete Nephthys ciliata. Cellular composition and interneuronal relationships in subepidermal and intramuscular areas of the nerve plexus are demonstrated. Morphological data are presented on a possible origin of typical associative and, presumably, motor neurons located outside the abdominal ganglion on the basis of differentiating primary sensory bipolars. Axo-axonal, axo-dendritic, and axo-somatic interneuronal contacts are shown in the nerve plexus. A characteristic feature of the studied peripheral nerve plexus of the body wall of the Nephthys ciliata is emphasized: the sufficiently intensive development of associative neuronal population. This provides a structural basis for peripheral integration of nervous processes in the central nervous system of the whole animal. Small groups of sensory and associative neurons described in the present study also seem to contribute to a relative autonomization of the peripheral part of the central nervous system of Nephthys ciliata. This can also be promoted by single suggested motor neurons of the plexus. The studied nerve plexus is actually deprived of typical associative-motor neurons that are so characteristic of the abdominal ganglion of polychaetes, oligochaetes, and leeches.