Fanworms

Serpulidae (fanworms) are very well-known polychaetes owing to their colourful radiolar crown. The crown is covered in densely packed microscopic projections that look like tiny hairs in a feather-like feeding and respiratory structure. This structure is attached to a lobe surrounding the mouth. Adult Serpulidae range in size from 2mm to well over 100mm.

Fanworms build hard tubes of crystalline calcium carbonate which are sometimes embedded in coral. The calcareous tube is usually white, though can also be blueish or pink, and is several times the length of the animal. Members of this family have a modified radiole (primary branch of the crown) which blocks the entrance of their tubes when they withdraw into the tubes.

These worms tend to have redish pigmentation on the radiolar crown and the forward part of their body. Some, such as christmas tree worms have white, yellow, orange, blue, brown or purple radiolar crowns.

1 species found on this page.

Christmas Tree Worms (Spirobranchus giganteus)

Christmas Tree Worms

(Spirobranchus giganteus)

Christmas tree worms are "polycheates", a sedentary worm living in hard corals. When they find a piece of live coral and burrow a home, they stay there.

Spirobranchus giganteus @ Koh Haa

They are small, about 3 - 4cm, but their bright colours and distinctive spiral shapes make them easy to spot. They can be found on hard coral formations in the reefs off Koh Lanta.

Their colourful "Christmas Tree" , feather like structures found on the surface of corals, are called Radioles. The main body of the worm in burrowed into the coral.

The feather like radioles, are the worms complex mouth appendages, allowing the worm to breathe and feed. By waving their feathers, they can catch passing plankton, moving it down to the mouth for eating.

Christmas Tree Worms @ Koh Rok

Christmas Tree Worms @ Koh Bida

The worms are very sensitive to movement and will retract in to their tubes if startled by shadows or moving objects. Wait a little, they will slowly open their tube and release their feathers.

Unlike other polycheates, Christmas tree worms have a third radiole, which covers the tube of the retracted worm, giving added protection. Although there are no real predators of adult worms.

This species reproduce by spawning and fertilising their eggs in the water, the larvae will then settle in the coral where it will burrow and grow into an adult.

Diving with Fanworms

If you'd love a chance to spot Fanworms on one of our daily Koh Lanta diving trips then send us an email to info@diveandrelax.com.

Join our high season speedboat dive trips to some of Thailand's best dive sites and enjoy small groups, short journey times, and a focus on great personal service, safety and fun.

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Find Out More

Allen, G., Steene, R., Humann, P., DeLoach, N. (2003) Reef Fish Identification, Tropical Pacific. Jacksonville, FL., USA: New World Publications, Inc., ISBN 1-878348-36-1.
Humann, P., DeLoach, N., (2010) Reef Creature Identification, Tropical Pacific. Jacksonville, FL., USA: New World Publications Inc., ISBN 978-1-878348-44-9
Debelius, H. (2013) Indian Ocean Reef Guide. Frankfurt, Germany: IKAN - Unterwasserarchiv, ISBN 978-3-939767-52-7.
Debelius, H. (2004) Nudibranchs and Sea Snails, Indo-Pacific Field Guide. Frankfurt, Germany: IKAN - Unterwasserarchiv, ISBN 3-925919-51-1
Erhardt, H., Knop, D. (2015) Corals Indo-Pacific Field Guide. Frankfurt, Germany: IKAN - Unterwasserarchiv, ISBN 3-925919-69-4.
Veron J.E.N., Stafford-Smith M.G., Turak E. and DeVantier L.M. (2016). Corals of the World

More Marine Life References and Further Information

(Serpulidae)

Christmas Tree Worms

Diving with Fanworms

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