Christmas Tree Worm Interesting Facts

Read more about the spectacular marine life such as the decorative Christmas tree worm interesting facts in our oceans in our marine life blogs.  Click here to read some fascinating facts about Frogfish facts for scuba divers.

Christmas Tree worms – Spirobranchus giganteus

To get into the festive spirit read about one of the favourite worms found on coral reefs around the world. They are affectionately known as Christmas tree worms. Divers can see them from Australia, through Thailand and Asia and then across to Caribbean sea.

They are one of over 13,000 species of segmented worms. But unlike their relative’s sea mice and feather duster they are pretty eye-catching

Christmas Tree Blog by All 4 Diving Liveaboards

They are found on the tropical reefs usually in shallow water, less than 30m of depth. The worms appear to have a preference for certain species of corals, but as yet scientists do not know why. Divers can see Porites with Christmas tree worms, or even Christmas tree worm rock during dives.  Some thoughts are they choose a species that parrotfish are not eating. Or ones that help when it comes to reproduction. The exposed part of the worm itself is not very large, about 3cm. But there is another part that can not be seen buried into the sub structure. They can vary in colour from white, blue, yellow, orange and red. This makes them easy to spot on the reef and one of the most photographs worms underwater.


As their name suggests, their appearance is quite distinctive due to the two spiral structures that protrude from the coral structure that resemble fir trees. The colourful spirals are in fact a highly developed structure the worms use for both feeding and respiration. 

The rest of the worm’s body is in a tube structure inside the coral substrate, this is formed when the worm is in its larval form. The worm settles on the coral, and this then grows around the animal leaving only the spiral structure radials exposed when feeding. The rest of the worm remains unseen and can be about twice the size of the visible part. The tubes are up to 17cm in length and are made from calcium carbonate that is excreted as a by-product of sane they consume.

One of the reasons the tubes are much longer than the animal is so they can retract inside when under threat for protection. They do however have a ‘door’ structure called an operculum they can close once they have completely retreated inside the tube-like their close relatives. This door has spines used to fend off its predators.

They are very sensitive to any motion, touch or even light and shadows and can quickly retreat inside the shelter of the tube when they occur. The worms are sedentary so do not really move.


The Christmas tree part of the worm has modified ‘promotion palps’ which are specialised mouths. Each spiral has feather-like radioles with many fine ‘hairs’ that can trap any prey ready for transport to the mouth. The main diet is microscopic plants, or phytoplankton, floating in the water. The water is pumped over the Christmas tree spirals which are covered in a sticky mucus which helps collect the prey. This is then moved in a conveyor type motion to the mouth. Larger particles are discarded only the smaller ones reach the digestive tract


There are both genders of Christmas tree worms, and they reproduce externally by sending eggs and sperm into the water. They then fuse and fertilisation takes place, the eggs then develop into larvae within 24 hours. The larvae can disperse for between 9 to 12 days before they will settle onto the coral substrate to grow.

Once they are established in the coral, they can live for an estimated 30 to 40 years, but more commonly 10 to 20 years.

Blog about Christmas Tree Worms by All 4 Diving Liveaboards

Christmas tree worm populations are stable at the moment, and there are few predators for any type of tube worm. They are noted as common in the oceans. The worms are an indicator of the health of coral reefs as changes in climate and habitat would affect their populations.

They are not harvested for food anywhere. But the aquarium trade has shown interest as they are very colourful and popular for photographers. Often the coral substrate is collected for the aquarium trade.

Images were provided by Jerry Arriaga