Nervous system, sensory structures and neurosecretion

Abstract

The detailed structure of the pulmonate nervous system has been described by Bullock and Horridge (1965). Most of the available information is based on the snail Helix and Kerkut and Walker (1975) dealt mainly with the nervous system of the snail H. aspersa in their review of the nervous system of pulmonates. The central nervous system of slugs is similar to that of Helix and has been described and illustrated for Vaginula solea d’Orbigny (Coifmann, 1934), for A. ater (Smith, 1967), for D. reticulatum (Runham and Hunter, 1970) and for the Athoracophoridae (Tillier, 1984). It consists of nine ganglia and their connectives which have become fused into a circumoesophageal ring. This ring lies immediately behind the buccal mass and can be divided into three parts: the supraoesophageal ganglionic mass, the suboesophageal ganglionic mass and the pedal ganglia. Slight differences occur between different groups of slugs in the length and thickness of the connectives and in the extent to which the suboesophageal ganglia are fused. For example, in some athoracophorid slugs the fusion is less complete and the outline of four suboesophageal ganglionic masses can be distinguished (Tillier, 1984). The arrangement of the circumoesophageal ganglia is shown in diagrammatic form in Fig. 6.1.