Some of the deep-sea squids possess a unique protective device. They discharge a luminous cloud to cover their escape. Other fish emit strong flashes of light to throw predators off target or temporarily “blind” them.

Quite a few near-surface organisms are luminescent. But in the deeper ocean levels where sunlight hardly penetrates, if at all, at least two thirds of the sea animals produce light. Says the above-mentioned researcher: “Some fishes, squids and euphausiids possess searchlights with reflector, lens and iris almost as complex as the eye.” Others, he says, may have luminosity that mimics a small group of luminous plankton, while some do “fishing” with a light that dangles in front of them. The unwary fish that approaches the “bait” is quickly swallowed up.