ABSTRACT
Kinematic studies reveal an integrated picture of a particular behaviour in that they reflect the interplay between the internal control of muscles and the external application of forces that produces the observed movement of the animal. Dynamical studies are required, however, to distinguish those movements that represent active force production by parts of the animal from passive movements imposed by externally applied forces or movements of other parts of the animal’s body. The combination of these two approaches produces a detailed and complete picture of the motions that characterize a behaviour. This description can prove instrumental in efforts to understand both the physiological basis and the functional significance of the behaviour because the movements that constitute a behaviour provide the interface between the underlying genetic and physiological control mechanisms and the function served by the act. This is readily grasped for continuing motor activities, but it is also relevant for behaviours characterized primarily by expression of a stable frozen posture. This chapter presents the defence posture and associated movements in crustaceans as an example of such behaviour.
