Iglesias, T.L., Boal, J.G., Frank, M.G., Zeil, J., and Hanlon, R.T. J. Exp. Biol. https://doi.org/10.1242/jeb.174862 (2018)

To sleep, therefore…to alternate between quiescent slow-wave sleep and rapid-eye-movement sleep. Such cycles are observed in most mammals, birds, and reptiles that are known to sleep. It occurs outside vertebrates too, including, as a recent report in the Journal of Experimental Biology demonstrates, cephalopods like the common cuttlefish, Sepia offinalis. In the current study, the researchers video recorded six cuttlefish and observed that the animals appear to experience a REM-like state: following a quiet period, the cuttlefish would twitch their arms, squint their eyes, and randomly change the patterns displayed on their skin. As in other sleepers, the behaviors were cyclical in nature, suggesting another animal that may be able to provide insight into the science of sleep.