van Swinderen, B. (2006). Sleep in Invertebrates. In Jon H. Kaas (Ed.), Evolution of Nervous Systems, Volume 1: Theories, Development, Invertebrates (pp. 451-456) Oxford: Academic Press. doi:10.1016/B0-12-370878-8/00185-3
This article discusses the importance of identifying sleep in invertebrates. Based on the studies of insects, arachnids, and crayfish, it notes that the criteria for sleep (e.g., behavioral quiescence, postural changes, decreased behavioral responsiveness, homeostasis, and neural correlates) are met in some key invertebrates. The need for sleep is likely to have evolved in invertebrates, and the article concludes that studying these animals may prove valuable to understanding the mechanism and function of sleep in general.