Bioluminescence ("living light") is the production of light by living organisms through a biochemical reaction. The general reaction involves a substrate called luciferin and an enzyme called luciferase, and requires oxygen. Specifically, luciferin is oxidized by luciferase and the chemical energy produced is transformed into light energy. In nature, bioluminescence is fairly widespread among a diverse group of organisms such as bacteria, fungi, sponges, jellyfish, mollusks, crustaceans, some worms, fireflies, and fish. It is totally lacking in vertebrate animals. Fireflies are probably the most commonly recognized examples of bioluminescent organisms, using the emitted light for mate recognition.