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.
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.
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.
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 Christmas tree worms.
Christmas tree worms 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.
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