The statocysts of cephalopods

This chapter details statocysts of cephalopods. The statocysts of most cephalopods are sense organs of great sophistication with macula/statolith systems that respond to gravity and crista/cupula systems operating as angular velocity transducers. Cephalopod statocysts, unlike those of most other invertebrates, have both primary and secondary sensory hair cells that have a unidirectional morphological and physiological polarization. Within the central nervous system, the sensory input from the statocysts is integrated into a variety of behaviors, including locomotion, posture, control of eye movements, and control of body-colour pattern. The sensory solutions to the problems of balance and orientation that cephalopods and vertebrates have evolved show close parallels. It is anticipated that a comparison of these two systems will give a greater understanding of the basic mechanisms which are important for the operation of all such sensory systems. Recent research has not only confirmed the statocysts as detectors of linear and angular accelerations, but has shown that their level of performance and sophistication rivals other such systems in the animal kingdom, including the human vertebrate vestibular system. Within the living cephalopod groups there are three main types of statocysts, discussed in detail in the chapter.