Nature's Night Lights

The transparent shells of tiny Cypridina hilgendorfii, found in the coastal waters and sands of Japan, hold a creature that emits a luminous blue substance when disturbed. During World War II, the Japanese harvested these creatures for soldiers to use when reading maps and messages at night.
(Photo shot on assignment for "Nature's Night Lights—Probing the Secrets of Bioluminescence," July 1971, National Geographic magazine)