This adorable creature is a Pom Pom Crab. It is very small, and doesn't typically survive long in captivity. The pom poms are actually tiny anemones. The crab puts them on like gloves! When the crab molts (shedding its exoskeleton) it recovers the anemones and puts them on the ends of it claws again. When it gets in a defensive situation, it waves the pompoms to scare away the predator. Reef-safe.
Photo by Gregr
Photo by Sinistard