Christmas Tree Worm – We wish You a Happy Holiday Season


For those who celebrate Christmas, tree decorating comes once a year, but in the world’s tropical seas, ’tis always the season! Christmas tree worms (Spirobranchus giganteus) are a type of polychaete a group of segmented worms that contains over 13,000 Species  And just like their cousins the sea Mice   and feather dusters unassuming invertebrates put on quite the eye -catching display.

To get into the holiday spirit, we’ve rounded up some of our favorite facts about these colourful creatures, starting with the obvious:

The common name for these worms is derived from their appearance with beautiful, spiraling plumes that resemble a fir tree., not their habitat or diet.

The “Christmas tree” shape shown in the images is the animal’s radioles, which can be up to about 1 1/2 inches in diameter. Each worm has two of these plumes, which are used for feeding and respiration. The rest of the worm’s body is in a tube in the coral, which is formed after the larval worm settles on the coral and then the coral grows around the worm.The worm’s legs (parapodia) and bristles (chatae) protected within the tube are about twice as large as the portion of the worm visible above the coral.

The  marine worm that lives on tropical coral reefs around the world.

Christmas tree worms come in a variety of bright colors. They aren’t very big, averaging about 1.5 inches in length. However, because of their distinctive shape, beauty, and color, these worms are easily spotted. They are some of the most widely recognized polycheates, or marine burrowing, segmented worms out there.

Christmas Tree Worm 1

The Seuss-style plumes you see above – which come in an array of colour morphs – are called “crowns”, and you’ll notice they appear in pairs. That’s because each worm has two of them. By pumping water up and over the crowns, a Christmas tree worm can filter out tiny plants and animals to snack on. The feathery structures are lined with both sticky mucus and spiky bristles (called cilia), which help trap passing prey.

Christmas Tree Worm 2

What are those branches actually for?

After a bit of size sifting, the worm moves any tasty morsels – conveyor-style – to the mouth, but the crowns do more than just catch food: they also harness oxygen! For this reason, the structures are often mistakenly called gills.

Underwater “pines” might be beautiful, but they’re really just the tip of this worm’s iceberg. Two-thirds of the body of a Spirobranchus lies hidden in a calcium carbonate tube, which it erects as a bunker.

An assortment of "trees". Image: Nick Hobgood
An assortment of "trees". Image: Nick Hobgood

Some groups take this one step further, by setting up shop in stony corals. But the crafty worms don’t do the heavy drilling: by nestling their bodies against the corals’ living tissues, they force the polyps to build around them. Over time, these coral-encased bunkers can reach ten inches in length.

Spirobranchus worms are pretty choosy about which corals they settle on, but scientists are still working out why. Some speculate that landing on carefully selected species could help the worms with reproduction. Others suggest the pickiness comes down to avoiding accidental predation (no worm wants a coral-munching parrot fish is hankering for its home turf).

Once settled down, a Christmas tree worm can live upwards of 30 years  (Though 10-20 is more common.)

While many invertebrates reproduce asexually, there are actually male and female Christmas tree worms. These animals are broadcast spawners, meaning they shoot their genetic contribution into the surrounding water, in the hope that it meets its match. Once fertilisation occurs, it takes just 24 hours for a larvae to develop.

If it worm feels threatened, it can withdraw into its tube to protect itself.

References: Ocean Service NOAA, Earthtouch News,


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December 11, 2017 |

2 thoughts on “Christmas Tree Worm – We wish You a Happy Holiday Season

  1. SusanLongIs says:

    I just love these critters! No matter where I go, I see them. Even on dives where there is perhaps less to see than others – these guys will always keep me entertained.

    Thank you so much for all of the details, SDR. I had no idea that they could live up to 30 years! WOW! And the spawning video was really cool.

    Sometimes I do feel a bit unwelcomed by these little guys. I swim up to say hi and they disappear 🙂

    Thanks for the post!


    • SDRStaff says:

      Thank you for your feedback. We will do our best to continue to provide entertaining & informative content. We also feel slighted many times by these little guys as well as other critters like garden eels.

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