Microscopic View into Christmas Tree Worm: UW Christmas!
Written by Roy Kittrell 6 December 2023.
For December’s article, we of course will be investigating the wonderfully named Christmas Tree Worm, otherwise known as Spirobranchus giganteus!
Almost anyone who has been diving or snorkelling has seen these colourful creatures poking out of holes in the coral, but few, including myself, ever really knew much about them or even what they were. If you’re like me, you probably assumed they were a kind of anemone or some other soft coral.
They are in fact however, a tube-building polychaete worm belonging to the family Serpulidae. They belong to the Phylum Annelida, an ancient phylum originating all the way back to the start of life on earth. This particular branch of worms evolved to have a large, colourful and very prominent prostomial palps in order to filter feed; in fact this is where it’s name comes from as they are shaped like Christmas trees. This is quite amazing, as this structure, present on all annelid worms, even the common earth worm found in your garden, is barely visible most of the time.
The worm begins it’s life as an egg, and then grows once it finds itself on some coral. It has the ability to secrete a calcareous tube to live in, which the coral then grows around, giving it a very safe and secure home to live in. This process takes a long time as you can imagine, and the worms are quite long lived; some of them can live as long as 40 years! As you will have seen, they have the ability to retract into their burrows and pull their modified radiola over their head as protection (see diagram below), or to stop fish like the Neon Goby from stealing food from it.
S.giganteus is an important reef animal. It has been found to be able to protect it’s host coral from being devoured by crown of thorns starfish, who wreak havoc on other unprotected corals. It’s also thought they can contribute to helping coral develop by increasing water flow over the surface and insulating them from warming ocean temperatures.
Join our 2024 dive trip and spot these little Christmas tree worms for yourself!
-Roy Kittrell is an avid naturalist and underwater photographer, his work can be found on Instagram @roythedivebro