Comb jellies, despite the name, are not true jellyfish at all, although their bodies are made up of a similar jelly-like substance. Instead of tentacles, these animals have teeth made of cilia (tiny beating hairs), which they use to eat other comb jellies. Their mouths can stretch wide enough to swallow an entire comb jelly of equal size. Comb jellies have plates of cilia all along the supporting "spines" of their bodies that reflect and refract light, much like fast-moving prisms. This makes for quite a pretty and mesmerising light show as the jelly moves through the water. They grow up to 15 cm in length.