In laboratory experiments, simultaneous continuous recording of the circadian cycle of behavioral reactions and cardiac activity of freshwater crayfish Astacus astacus and Procambarus clarkii was carried out. A non-invasive fiber-optic method of recording of the heart rate (HR) was used. The obtained data were analyzed by the method of variational pulsometry (VP). It was revealed that certain values of HR and characteristics of VP corresponded to the physiological states of active wakefulness and rest. It was found that during long immobilization of crayfish it is possible to identify the states of operative rest and sleep by the animal behavioral reactions and parameters of cardiac activity. Crayfish were studied in the state of artificially evoked immobilization ("animal hypnosis"). During this state, a high HR level, an increase of indexes of tension and autonomic equilibrium, and changes of other VP characteristics were observed. It is suggested that the different level of cardiac activity in different physiological states of crayfish (active wakefulness, operative rest, sleep, and "animal hypnosis") is regulated by nervous influences analogous to sympathetic and parasympathetic influences in vertebrates. It was concluded that freshwater crayfish as a representative of the highly organized invertebrates can serve an effective model for studying mechanisms of sleep-like states and "animal hypnosis" in animals.