The anglerfish is a horrifying looking, deep sea fish that is well known for having a lure on the top of its head that is bioluminescent, creating light. Bioluminescence occurs as a chemical reaction, oftentimes from bacteria, when certain molecules called luciferin and luciferase come into contact and react with oxygen. The "rod" on the anglerfish that connects to the top of the head is called the "illicium", which is a modified dorsal fin (the fin on the back). The end of the illicium is connected to the "esca", which is a fleshy bit that contains the bacteria creating the bioluminescence. The anglerfish uses this modified, special appendage to attract prey in the dark depths of the ocean. The anglerfish is a horrifying looking, deep sea fish that is well known for having a lure on the top of its head that is bioluminescent, creating light. Bioluminescence occurs as a chemical reaction, oftentimes from bacteria, when certain molecules called luciferin and luciferase come into contact and react with oxygen. The "rod" on the anglerfish that connects to the top of the head is called the "illicium", which is a modified dorsal fin (the fin on the back). The end of the illicium is connected to the "esca", which is a fleshy bit that contains the bacteria creating the bioluminescence. The anglerfish uses this modified, special appendage to attract prey in the dark depths of the ocean.