why jellyfish need to sleep too

Jellyfish and the researchers who study them confront a basic problem: these animals lack a central nervous system, so there is no clear consciousness to lose when sleep begins.

Researchers tested Cassiopeia jellyfish, a species that often rests upside down, to see whether their responsiveness changes across day and night cycles.

Researchers studying jellyfish subjected the animals to sustained disturbance to test whether their activity patterns change after a night without rest.

Sleep researchers evaluating animals without centralized brains need objective behavioral rules to decide when these organisms are truly asleep rather than simply inactive.

Jellyfish and humans both depend on sleep even though only humans have consciousness, showing that sleep is tied to basic biology rather than complex self awareness.

Jellyfish represent a very early branch of animal life, and humans diverged from them hundreds of millions of years ago, long before complex nervous systems evolved.