The Christmas Tree Worm on the left is one of my favorite creatures on the coral reef. I was introduced to them by another diver on the Great Barrier Reef off Queensland, Australia in 1994, and they are also present on the coral reef in Belize. The single worm puts out two "brushes" at about 30 degree angle from each other, each about the size of the tip of my little finger. The cilia of the brushes vibrate to aid in filter feeding. I love the way they snap back to hide within their little tunnel in the flick of an eyelash when you flick your finger close to them. They wait a few minutes before venturing out again. Of course we never actually touch the worms or anything else around the coral reef ecology, as everything can be seriously hurt by a mere touch, excepting sandy bottoms and other divers.
The Christmas Tree Worm on the right is on a Brain Coral, with its maze-like corrugations. These worms are relatively rare on our dives in Belize, but we saw at least one on most dives.
The Feather Duster on the left is another strikingly beautiful worm that lives on coral structures. It is about 1" long. These are less common than the Christmas Tree Worms. I don't think I have ever tried flicking a finger at one of them, so I don't know if they too will instantly retreat.