Joy to the Worm

Once again, Mother Nature has outdone herself with the razzle-dazzle. Meet the Christmas tree worm, a marine species that burrows into corals from the Caribbean to the Indo-Pacific. Far removed from its earthworm cousins and from the world of snow and fir trees, Spirobranchus giganteus (hardly gigantic at just a few inches tall) puts on a stunning display. From a tube that houses its main body, the worm unfurls a set of spiraling, feathery tentacles. These crowns, called radioles, come in a rainbow of hues from Smurf blue to tangerine. Some even have tiny white tips resembling Christmas tree lights. But the radioles aren’t just for show; they filter food, serve as gills for respiration, and include motion-sensitive eye spots. 

If you’re snorkeling or diving in the Great Barrier Reef and you happen upon these magical specimens, don’t come on too strong—when they sense danger, Christmas tree worms will quickly close up shop and retreat into tubular safety. This quick reflex serves them so well, the homebodies can live as long as 40 years anchored in the same spot. To reproduce, the worms release their sex cells into the ocean for fertilization—the larvae then land on their own corals and get burrowing.

As with so many creatures on the planet, corals and worms share a symbiotic relationship: A coral provides a safe home for the worm, while the worm helps protect its host from predators such as the crown of thorns. Already beat up from ocean acidification and bleaching caused by climate change, reefs are increasingly threatened by these large, ravenous starfish. Christmas tree worms appear to irritate the starfish, or at least make it harder for them to consume the corals’ soft flesh. This holiday season and beyond, the coral-worm partnership offers a reminder that we’re all stronger together.

Watch this short video to see Christmas tree worms in action.