Moon jellyfish are the first species in which scientists have observed "symmetrization." Jellyfish are one of the preferred food sources for most sea turtles, and are nibbled at astonishing rates. A study in 2010 showed that at least one third of oceanic invertebrates, including jellyfish, are recovering from an injury at any point in time.
Lots of invertebrates can regenerate their limbs, but this is the first species noticed where there is no new tissue generated. According to researcher Michael Abrams, a graduate student in biological engineering at the California Institute of Technology, "We've now observed another self-repair mechanism. It kind of broadens our definition of self-repair."
Abrams and his advisor, professor Lea Goentoro, were initially trying to study the immortal jellyfish, or Turritopsis dohrnii, a species that can switch to its polyp stage and start the process of developing into an adult all over again, effectively allowing it to live forever. While their lab waited for specimens to arrive from Japan, Abrams decided to practice his techniques with some common moon jellyfish.
Abrams started performing amputation experiments to se how the moon jellies responded. Almost immediately, he noticed that something was different about how these jellyfish reacted to injury. After losing a limb, the juvenile moon jellyfish began to rotate their arms until they were evenly distributed around their bodies.
Between 72 and 96 percent of the moon jellies tested were able to revert to a perfectly symmetrical form again. Specimens that failed to regain symmetry grew extra stomachs and floundered at the bottom of the tank. The team discovered that without any cellular reactions occurring, the pulsating movement of the jellyfish was enough to realign its limbs so that they were more symmetrical. When they were anesthetized, the lack of movement prevented them from rearranging themselves.
The findings of the study were published in the journal Proceedings of the National Academy of Sciences.