Their Christmas tree-like crowns are composed of radioles, whispy appendages which radiate from the worm's central spine. These appendages are used for respiration and to catch dinner, usually microscopic plants, or phytoplankton, floating in the water.

These worms are sedentary. Once they find a place they like, they remain. They anchor themselves by burrowing into live coral, usually living out their lives in that spot. In these photos the worms have selected brain coral and star coral. When startled, usually by the approach of a diver's camera or a hungry fish, the worms rapidly retract into their burrows, becoming invisible to the intruder or potential predator.  The seem to be sensitive to light and will retract when covered by an approaching shadow.