BEACON TRANSCRIPT – A recently captured video gave rise to its fair share of questions and wonder as scientists spotted a Cassiopea jellyfish enter a sleep-like state. This was quite an unexpected find, as research has yet to determine if sleep is common among invertebrates. It is also the first time that a creature without a brain was noted to be sleeping.
Cassiopea Jellyfish, Odd Not Only Because of Their Upside-Down Nature
Scientists agree and are aware that all of the vertebrate animals studied as of yet sleep. However, they are less certain if invertebrates or creatures without a brain or central nervous system are also doing it. So a team of Howard Hughes Medical Institute at Caltech researchers set out to solve this mystery.
To do so, they studied an unusual jellyfish, known for its being upside-down, the Cassiopea, the only member of the Cassiopeidae family. Such specimens can usually be found in mangrove swamps, mudflats, or other warm shallow waters, and are mostly stationary.
The research team sought to determine if the Cassiopea jellyfish moves continuously, or if they just pulsate at a steady rate, so they filmed them at night. Several specimens of the genus were followed over a period of six days and nights.
This revealed that the jellyfish seemed to enter a sleep-like state at night. The team explained that the specimens’ constant pulsing slowed down at night. However, this also became alert and steady once again as the scientists dropped bits of food in their tanks.
Further observations of the jellyfish as they were standing on a suspended mesh floor revealed that, as the mesh dropped out from under them during the day, the invertebrates were quick to swim to the bottom of the tank.
The same could not be said about their nighttime reaction, which was reportedly much more sluggish in nature. Also, the team noted that, after a night of disrupted “sleep”, the Cassiopea jellyfish pulsated less often.
According to the team, this proves that the species slumber at night, and can feel the effects of a night of disturbed rest.
New Questions Arise About Sleep
The research team considers that their having demonstrated that jellyfish do, in fact, “sleep”, only helped raise more questions.
“Do you need neurons to sleep? Do you need more than one cell to sleep?”, asks Paul Sternberg, a study co-author.
Their findings seem to indicate that the origin of sleep goes even further back and before the emergence of a centralized nervous system.
“It’s the first example of sleep in animals without a brain,” as Sternberg accentuates. He reportedly intends to study sponges, and see if perhaps these are also capable and enter a sleep-like state as well.
Study results are available in a paper in the journal Current Biology.
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