From The Featured Creature:
Swimmingly peacefully through the dark waters of the ocean the world over are marine planktonic polychaete worms in genus Tomopteris. These mesmerizing creatures are relatively transparent until they shine a deep bioluminescent blue. One species, Tomopteris nisseni, is one of the few creatures on the planet to produce yellow bioluminescence.
Others in this genus are capable of dispelling a flurry of bioluminescent sparks from their parapodia. This is used to distract predators, making them go after the discharged glow instead of the actual animal.
They only reach a few centimeters in length, not counting the full tail length which varies and their antennae, but no matter the size of this spectacular creature it’s impossible to take your eyes off its captivating undulating body as it rhythmically slinks through the darkness.