The adaptation is ancient: Ink sacs are present in fossils of octopus ancestors that are more than 300 million years old. Photographed at Dive Gizo, Solomon Islands Octopuses and cuttlefish that ...

Most octopuses have an ink sac as a defense mechanism. The octopus can spew ink into the surrounding water to scare predators away — or befuddle the enemy while they make their getaway.

Like its close relatives, the squid and octopus, the cuttlefish is equipped with an ink sac that can help it make a last-ditch escape from predators that hunt by sight. The cuttlefish can eject ...