The Science of Sleep Sleep has been presumed to require a brain, but recent experiments with jellyfish suggest that even organisms without a brain need to sleep, and suffer disorientation if deprived.

Article: https://www.washingtonpost.com/news/speaking-of-science/wp/2017/09/21/scientists-just-discovered-the-first-animal-without-a-brain-that-sleeps/?utm_term=.c1e777be6a8a