Christmas Tree Worms
These are Christmas Tree Worms - Spirobranchus giganteus, living in a colony of Porites. They are symbiotic, in that once the coral dies, the worm does too. Christmas tree worms come in many colors, and you may obtain a colony with four, five, or six different colored trees. When frightened, the worms will quickly retract into the coral, pulling their crown out of sight. The crown is used to trap plankton-sized food from the water for its meal. Reef-safe
Below, more Christmas Tree Worms living in some pocillopora.