The proboscis of Bonellia viridis Rolando, 1822 females is the best studied among the echiurids and the rich data are extrapolated to other species of echiurids. However, very little is known about the fine structure and general organization of the nervous system of B. viridis and echiurids as a whole. The microscopic anatomy and ultrastructure of the nervous system of the proboscis of B. viridis are studied by the use of histology, micro-CT, SEM, TEM, and CLSM. The nerve cord, which forms a nerve loop, runs along the edges of the proboscis and gives rise to a number of peripheral nerves. For the first time, multiple radial neurite bundles innervating the margin of the terminal lobes and the frontal nerve passing along the margin are described. These nerves innervate the huge aggregation of glandular cells of the margin. The presence of additional nerve elements along the margin of the terminal lobes is determined by the specific function of the margin, which is used for the attachment of the proboscis to the substratum and for collection of food particles. The nerve loop of the proboscis has a typical structure: perikarya are located on the pe-riphery of the nerve cord and the nerve projections extend into its centre. Among the nerve projections, the giant nerve fibre is defined. Neurons of four types, which differ from each other in the fine structure of soma, are described in the nerve loop. Some perikarya exhibit serotonin-like immunoreactivity. Specific cells, which contain intermediate filaments that are anchored to the basal lamina via hemidesmosomes are described for the first time and are identified as radial glia. We have suggested the origin of certain structure of echiurid nerve cord as a result of ingression of stratified neuroepithelium of annelid-like ancestor.