Experiments suggest that upside-down jellyfish are the first brainless animals that snooze
The life of a jellyfish may seem like a real snooze, but until now biologists were never certain if the gelatinous blobs actually slept. Now it appears that at least one group of jellyfish needs its beauty sleep just like us.
Some species of upside-down jellyfish (Cassiopea) meet all of the criteria for entering a “sleeplike state,” a group of Caltech researchers report September 21 in Current Biology. The jellyfish seem groggy after a sleepless night and quickly waken from their slumber when fed, experiments show.
It’s a surprising find: Sleep and sleeplike states have been documented in a wide range of animals — from microscopic wormlike nematodes to, of course, humans (SN: 10/24/09, p. 16). But until now, the behavior has been observed only in