Christmas Tree Worms

Note: Students from Celeste Young's biology class (Monument Mountain Regional High School; Great Barrington, MA) posted a question for Aquarium researcher Dr. Randi Rotjan in the comments section of this post. Here is Susanna's question with Randi's answer in light blue:

Hello! This is Celeste Young & her biology class! What is the scale of the christmas tree worm picture?

Hi Celeste and Susanna,

Thanks so much for reading the blogs, and for posting your question!

Christmas tree worms are small-- the crowns are only a few centimeters across, at most. They are hard to measure, since they actually retract their plumes (or branchial crowns) into their tubes with the slightest disturbance in the water. Tubes are made of calcium carbonate. These worms settle on the surface of a coral (they do not bore into the skeleton) and grow at roughly the same pace as the coral tissue - thus, they grow really slowly! Some worms are known to be up to 40 years old, so they also can live a very long time. Worms feed by filtering plankton from the water column with their branchial crowns. They retract into their tubes to avoid predators (and rulers). The best way to add a ruler to the photo is to place the ruler down, let the worm retract, and then re-emerge. However, this only works in very calm water, with high flow, the ruler will not stay in place! :-)

Check out the photos below of an exposed worm (left); and then the same worm retracted into its tube (right). These photos were taken by a student of mine, Sarah Abboud, who is actually studying these worms for her masters thesis. These photos are taken from Moorea, French Polynesia, but are of the same species of worm that we observed in the Phoenix Islands.

Spirobranchus giganteus christmas tree worm - exposed and retracted. (Photos: S. Abboud)

Below is another worm next to a piece of flagging for scale. The flagging is 2.5 cm across, so you can now estimate the size of the worm crown!

Spirobranchus giganteus christmas tree worm - exposed 
Here are some additional photos by Sarah, measuring the diameter of the tube. Tube diameter correlates to worm age, but not to crown size. Crown size varies with depth; worms in deep areas with high water flow (surge) actually have shorter crowns so that they don't bend or break when water is rushing past them. Deep areas with low surge have taller crowns. Here are some scale bars next to worm tubes; the left photo has an exposed worm behind the 1 cm scale bar (it's orange).

Spirobranchus giganteus christmas tree worms - retracted. (Photos: S. Abboud)

Finally, here's a worm retracted, but just barely: you can see it's crown folded within the tube, and just breaking the surface.

Spirobranchus giganteus christmas tree worm - retracted. (Photos: S. Abboud)

The photos on The Slow and the Spineless post were not taken for an explicit scientific purpose, thus, there are no scale bars on those photos. But I hope that this gives you an idea of scale, nonetheless.

Thanks again for your question!

Best fishes,




  1. Randi I wanted to ask you why it is that all the christmas tree worms I see have two crowns? Is it two crowns on one worm or two worms each with one crown? Is it always two?

  2. Hi Johann,

    Yup, there are paired crowns on a single worm. As far as I know, all Spirobranchus have paired crowns, but that's not true of all Serpulid polychaetes. You can read more on Serpulids here:


    Thanks for reading!


  3. Celeste Young teaches Biology at Monument Mountain Regional High School in Great Barrington, Massachusetts