Detached tissues from the appendages of a scarlet sea cucumber (Psolus fabricii) survived for more than three years in flowing seawater without special nutrients or antibiotics, researchers reported on May 29 in Science Advances.

The initial observation occurred during a routine transfer of a scarlet sea cucumber when a colleague of marine ecologist Annie Mercier noticed the animal had left a few podia on the bottom of a tank. Podia are small tubelike appendages that sea cucumbers use for movement. Mercier, a marine ecologist at Memorial University of Newfoundland in St. John's, Canada, and her colleagues explored what would happen to other ethically-sourced tissues cut off with a scalpel, including tentacles and parts of the body wall. The body wall tissues died within weeks, but the tube feet and tentacles survived for more than three years.

"We would have expected those to decay and waste away quite rapidly, but several days later they were still there," Mercier said. Researchers observed that the living tissue underwent a cleaning process of the wound where it was cut, which involved clearing out old dead cells and subsequent division of living cells. The tissue also did not decay after being buried in a couple of centimeters of mud. Researchers added amino acids labeled with a trackable atomic tag to seawater and observed the tissue absorbed the nutrients. "We started calling it our 'zombie project,'" Mercier said. "It's a piece of tissue that isn't decaying. It's still acquiring nutrients, reshaping itself, evolving and doing all sorts of living things, yet it's not necessarily a living organism in the traditional sense."

José García Arrarás, a regenerative biologist at the University of Puerto Rico in San Juan who was not involved with the research, commented on the finding. "It's an amazing finding, but not entirely surprising given the sea cucumber's remarkable capabilities," he said. "But [the work] raises fascinating questions." He noted the work could offer new ways to study changes that occur during aging, explaining, "You need to know exactly what you have before you can understand what's going on."