Echinoderms are survivors. Many of the marine invertebrates—such as starfish and brittle stars—can regrow lost limbs, and some will even shed an arm or two to escape a predator. Their spiky sea urchin cousins are known to replace lost spines. Now, seafloor images taken off the coast of Norway have revealed a new high-water mark for the tenacious sea urchin: Despite having a gaping hole where its anus and sexual organs used to be, one severely injured Strongylocentrotus kept moving for at least 43 hours and 20 minutes, at one point even dodging an attack from a hungry crab (above).
The reason the tough little critter survived its fatal-looking wound, scientists say, is because sea urchins have no real brain. Instead, they have a decentralized nervous system, one that largely survived in our protagonist’s injury. The team isn’t sure what caused the damage—which tore off half of the urchin’s upper shell, exposing its jaw and intestines—but they suspect it was a predatory fish or a crustacean, they write in Polar Biology. Alternatively, they grimly concede, “It might have been us scientists who caused the injury by accident when deploying and documenting the lander platform.”
Also unclear is whether the sea urchin survived after the lander stopped recording. Because the remains of many recent and fossil urchins seem to have healed sizable fractures, the researchers say their subject likely lived long enough to begin to regenerate. After all, what doesn’t kill you makes you Strongylocentrotus. Ahem, stronger.