Jellyfish Sleep, and Now Scientists Wonder If Plants and Bacteria Sleep Too

The discovery that jellyfish go to sleep is making scientists rethink when sleep first evolved, what it actually is, and how it helps us and other snoozers.

Published On 09/21/2017
5:00 PM EDT
J J ellyfish lack ears, eyes, a nose, a heart, bones, and a brain. In fact, they don’t even have a head. Their states of being, as they float and pulse rhythmically in water, have therefore mostly been unknown.
“If jellyfish dream, what would they dream about?”
Caltech footage of the jellyfish Cassiopea.
Multiple Cassiopea jellyfish. The animals prefer to sit upside down on the floor of the water column. | Caltech