Ctenophores, or comb jellies, are gelatinous organisms that cruise the oceans using the rows of cilia which line their bodies. They’re simple in design, and very beautiful to watch as the cilia produce shifting rainbows of color. We occasionally had these at the aquarium where I used to work, and everyone — staff, volunteers and visitors — found them mesmerizing.
For seven other sea creatures that make their own light, check out this slide show at Wired. (The photo of dinoflagellates lighting up a wave is gorgeous.)