Corals sleep like us, but their symbionts never rest

Sleep is essential for much of the animal kingdom. During the night, neuron and tissue repair mechanisms are activated to aid recovery from daily activity. This is risky: organisms that sleep are more vulnerable to predators. However, the phenomenon extends from mammals to invertebrates. Nevertheless, until now it was not known whether other, more ancient groups without neurons, such as corals, engage in any kind of nocturnal rest.