For Jellyfish, Symmetry is More Important than Regenerating Limbs

Written by on June 24, 2015 in Jellyfish, Marine Life

Self-repair is an incredibly important trait for survival in the animal kingdom. Many living things have the ability to repair damaged tissues, from healing small scratches (like humans) to regenerating entire limbs (like some lizards). Now, new research reveals that some jellyfish have a unique and previously unknown self-repair mechanism.

Moon jellies.

Moon jellies. Photo credit: brianandjaclyn via photopin cc.

Scientists have long known that some jellyfish can rapidly regenerate tissue by growing new cells to replace ones lost to injury. The hydra, a jellyfish-like organism, is often used as a model to study regeneration. Researchers at Caltech wanted to know if moon jellyfish (Aurelia aurita) respond to injuries in the same way.

To do this, the researchers performed amputations on anesthetized moon jellies, removing one to six arms. The animals were then returned to their tanks to be monitored. In order to make it easier to see regeneration taking places, the researchers focused their study on the juvenile (ephyra) stage because the moon jellies are in a simple disk shape with eight symmetrical arms.

While the wounds healed just as expected, the researchers were surprised to learn that the jellyfish were not regenerating tissue to replace the lost arms. Instead, the juveniles reorganized their existing arms to regain symmetry, even if they had just two arms left. The researchers observed a similar process in three additional species.

“This is a different strategy of self-repair,” Caltech assistant professor of biology Lea Goentoro explained in a news release. “Some animals just heal their wounds, other animals regenerate what is lost, but the moon jelly ephyrae don’t regenerate their lost limbs. They heal the wound, but then they reorganize to regain symmetry.”

There are several reasons why jellyfish might prioritize resymmetrization over regeneration. Jellyfish have “radial symmetry”, which means they have a distinct top and bottom but no distinguishable left or right sides. Radial symmetry is essential to how they swim and eat.

“Jellyfish move by ‘flapping’ their arms; this allows for propulsion through the water, which also moves water—and food—past the mouth,” graduate student Michael Abrams said. “As they are swimming, a boundary layer of viscous—that is, thick—fluid forms between their arms, creating a continuous paddling surface. And you can imagine how this paddling surface would be disturbed if you have a big gap between the arms.”

Additionally, the small group of jellyfish that didn’t resymmetrize (about 15%) weren’t able to develop into normal adult jellyfish.

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Copyright © 2015 by Marine Science Today, a publication of Marine Science Today LLC.

About the Author

About the Author: Emily Tripp is the Publisher and Editor of She holds marine science and biology degrees from the University of Miami's Rosenstiel School of Marine and Atmospheric Science and a Master of Advanced Studies degree in Marine Biodiversity and Conservation from Scripps Institution of Oceanography. When she's not writing about marine science, she's probably running around outside or playing with her dog. .


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