The Christmas tree worm (Spirobranchus giganteus) is a type of polychaete, a group of segmented worms mostly found in the ocean. It lives on tropical coral reefs and resembles a fluffy fur tree adorned with colored ornaments. Each worm has two tree-like appendages that are used to breathe and to catch meals of plankton floating by.
The Christmas tree worms are sedentary, attaching themselves to coral cover that acts as their home base. Once attached, they create a calcium carbonate tube that they can then retract into for protection. The fluffy, eye-catching section of the worms that attract divers are small in size, usually not bigger than a few inches, but the remainder of the worm (hiding in its burrow) can be almost twice that size.