Bristle worm. Saltwater. Feather Duster Worms. Worm colony, which normally consists of dozens of similar rigid tubes sheltering serpulid worms. The worms use their exposed tentacles to catch drifting bits of food. They are extremely sensitive to changes in light and will withdraw completely within a split second if disturbed. The tubes are small, with an inner diameter of a pencil lead, and are usually found in shaded areas underneath coral heads, out of direct sunlight.