What does it mean to be alive? A new study on an astonishing sea creature suggests the answer may be more complicated than it seems.Some amputated fragments of Psolus fabricii — a type of sea cucumber native to the North Atlantic Ocean — puzzled researchers when they noticed that the severed parts did not simply decay and die but instead appeared to grow.To find out more, the researchers humanely excised additional fragments from the feet, main body and tentacles of the marine animals and ran a number of lab experiments in untreated seawater. Indeed, the fragments refused to die. The various parts unexpectedly healed themselves and even managed to absorb nutrients despite lacking a mouth.AdvertisementAdvertisement“This is the first case of tissue immortality in natural conditions,” said Sara Jobson, lead author of a study describing the finding that published Wednesday in the journal Science Advances. “These sea cucumbers are known for their high-regenerative capacity, so when they lose a tentacle or a tube foot they’re able to regrow it very well, but nobody’s ever looked at what happens to the tissues that are torn off, because we just assumed that they would die.”The severed tissues, however, didn’t develop into whole new individuals — a process that can occur under certain conditions in some species of sea cucumber — bringing up some philosophical questions. “We lovingly call these tissue explants ‘our zombies,’ because they seem to ride the line between dead and alive,” said Jobson, a doctoral student of ocean sciences at Memorial University in Newfoundland and Labrador.Tube foot tissue one year (top) and several years (bottom) after removal from a sea cucumber shows the wound site over time. – Sara Jobson“They’re not regrowing into a whole new organism — as far as we can tell, they seem to be their own entity that’s maintaining cellular function, but not a reproducing individual. Why would these small tissue chunks maintain the ability to heal and survive without any reproductive purpose? …
