Sept. 21 (UPI) — Scientists have observed, for the first time, a jellyfish in a sleep-like state. It’s the first time an animal without a brain or central nervous system has been observed sleeping.

The findings — detailed this week in the journal Current Biology — could help scientists finally answer the questions: Do all animals sleep?

All vertebrates studied by scientists sleep, but researchers haven’t been able to agree whether or not sleep is ubiquitous, or even common, among invertebrates. Studies have suggested fruit flies and roundworms sleep, but what about more primitive organisms like sponges and jellyfish?

Read more