They might be brainless, but even jellyfish need sleep.
Three graduate students at the California Institute of Technology in Pasadena, California, studied the late-night habits of the Casseopia jellyfish. The sea creature has a net of nerve cells, but no brain to speak of. It sucks in food through pores in its tentacles. “They’re weird plant animals,” says Claire Bedbrook, one of the graduate students who conducted the study, in a Sept. 21 article in The Washington Post.
They tested for three criteria—reversible quiescence (meaning the jellyfish were inactive but not paralyzed), an increased arousal threshold (meaning it’s harder to get the animals’ attention) and a need to sleep. To test this last criterion, the researchers poked them with pulses of water every 20 minutes all night. The next day, the jellyfish seemed dazed and the next night they appeared to sleep more deeply, the article reports.
The research, published in the Journal of Current Biology, raises interesting questions about the nature of sleep.
“The results suggest that sleep is deeply rooted in our biology, a behavior that evolved early in the history of animal life and has stuck with us ever since,” the article states.
If scientists can discover why brainless jellyfish need sleep, then maybe it can lead to finding the function of sleep in humans, the article notes.