The cephalopod nervous system: What evolution has made of the molluscan design

Abstract

The cephalopod nervous system is the most complex of any invertebrate nervous system. Although species-specific differences exist, its high level of complexity almost certainly is due to the cephalopods’ very active, fast-moving, predatory life style, and their complex behavior and extreme flexibility of response to different environmental situations. Nevertheless, the basic morphological plan of the cephalopod nervous system is still of the ganglionated “molluscan” design. During the course of evolution some of the ganglia became increasingly complex and subdivided into lobes; also, new ganglia were added. This chapter describes the basic morphological plan of the cephalopod nervous system and outlines some species-specific differences that developed as adaptations to different life styles. Special emphasis will be given to those features of the cephalopod nervous system that, within the invertebrates, are unusual or even unique, often rivaling the equivalent parts of the vertebrate nervous system in sophistication; some of these features may characterize higher brain and nervous system function.