Name: Meet the Marvelous Christmas Tree Worm
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Instead of slithering through soil, the Christmas tree worm inhabits coral reefs and might even help protect them against destruction.

This festive-sounding relative to earthworms might help protect coral reefs.

Instead of slithering through soil, the Christmas tree worm inhabits coral reefs and might even help protect them against destruction.

Meet the Marvelous Christmas Tree Worm

This festive-sounding relative to earthworms might help protect coral reefs.

Nature

Meet the Marvelous Christmas Tree WormPublished: January 4, 2022Narrator: Is there anything more festive than a Christmas Tree... worm? Known as Spirobranchus or “spiral gills” when roughly translated from the Latin, the Christmas Tree Worm is a marine animal, distantly related to earthworms. Though you might notice it looks a LOT different from your ‘garden variety’ nightcrawler. Instead of slithering through soil, the Christmas tree worm inhabits coral reefs and might even help protect them from destruction. And unlike a nightcrawler’s average lifespan of 6 to 9 years, or even 20 years in some recorded cases, a Christmas tree worm has an AVERAGE lifespan of 10 to 20 years and can even live up to 40 years in an unpolluted habitat! Another major difference is this worm’s uniquely shaped headgear — two projections covered in gill-like organs called radioles, which the worm uses for feeding and breathing. These “crowns” resemble a twin pair of brightly colored fir trees sprouting from the reef, and they actually help protect corals from encroaching predators. But more on that in a minute.First, let’s look at what this creature eats. The Christmas tree worm’s radioles are lined with small hairlike projections called cilia, which the worm uses to snag plankton drifting by in the ocean current. These cilia carry unlucky riders straight to the worm’s hungry, waiting mouth.Of course, the Christmas tree worm doesn’t want to get eaten itself, so it comes equipped with a handy escape hatch, literally. When it encounters a predator, the Christmas tree worm quickly retracts into its burrow, and blocks the entrance with a piece of its own body, a modified radiole called an “operculum.” Sealed shut and surrounded by a coral fortress, the worm forces would-be predators to look somewhere else for a meal. This strong defense is very important, since adult Christmas tree worms have nowhere to run.Lyndon DeVantier: Unlike nearly every worm, they don't wriggle, they don't move, they just stay put. The larva finds a little niche on the coral, on the living coral, and very quickly, it metamorphoses into a tiny worm and secretes a little tube that it then inhabits. And then as the coral grows, which is at about a centimeter or so a year, the worm builds its tube inside the growing coral. And so you end up with this coral living right up to the edge of the tube of the worm and so as the coral is increasing its height, the worm increases its height with it. These are really, really successful animals.Narrator: So successful that they thrive in tropical ocean environments worldwide from the Pacific to the Caribbean.The Christmas tree worm also acts as an aquatic guard dog protecting its coral reef home from voracious predators like the crown-of-thorns starfish — a roughly foot-and-a-half long, spine-covered behemoth. Like a herd of heavily armored undersea cows, these starfish graze their way through coral reefs. In just one year, each crown-of-thorns starfish can graze up to about 108 square feet. That may not seem like much, but that each female can produce up to 50 million eggs! It’s no wonder that, along with cyclones and climate change-related warming temperatures, these starfish outbreaks have led to an estimated loss of 50% of coral in the Great Barrier Reef since 1995.This is where the Christmas tree worm comes in. As the crown-of-thorns starfish makes its way across the reef, it runs into the worm’s radioles, which instinctively push away the starfish’s encroaching appendages and stomach.DeVantier: I think the fact that they protected against the crown-of-thorns wasn't a particularly conscious decision on the part of the worms. It’s just that the worms, by being there, are a sufficient irritation to the starfish that it discourages the starfish from eating on top of the worm because the worm can open and it can push and it can irritate the feeding stomach that the starfish spreads out across the corals.Narrator: Lyndon DeVantier even wonders if these worms might inadvertently help insulate corals from rising sea temperatures, with their radioles providing shade and increasing water circulation. Certainly, a potential avenue of future study.So let’s recap. We have an unintentional marine bouncer that eats with its tree-shaped lung-like organs. That’s certainly not something Santa would expect to encounter on a cold Christmas Eve. But thanks to its role protecting coral reefs, this colorful worm has probably secured a spot on the jolly man’s nice list.

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Meet the Marvelous Christmas Tree Worm

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