Fan worms are among the many sessile reef animals that make a living by filtering food out of the water. There are many species of fan worms and they are found in most of the world's oceans from intertidal to deep depths. Their specialised, sometimes colourful fans serve several functions: food collection, breathing and sorting sediment particles to use in their tubes. Their tubes can be made of limey calcium carbonate or of a range of different sized sediment particles and lengthens as the worm grows.

• An annelid worm with many fine bristles or hairs extending from each segment of your body
• Live a sessile existence with most of your body hidden in a tube.
• Have two sections in your body: a strong front section (thorax)with few segments and a more sac-like back section (abdomen)with many segments.
• To feed on small particles in the water using a frilly crown of finely divided tentacles, each covered with many microscopic, beating hairs (cilia).
• Use your crown of tentacles to breathe as well as eat.

Fan worms, feather duster worms, Christmas tree worms, Sabellids, Serpulids, Sabellarids.

Most people see only the business end of fan worms - the frilly crown of tentacles used to feed and breathe. The crown may be formed of one or two whorls and comes in a variety of colours: blue, yellow, white, orange, red and less stylish colours such as brown and grey. Off to the side you might see a white plug-like structure with spiky branches. This is the operculum, or door that closes off the tube when the worms retreats inside. Inside the tube, the worm is bilaterally symmetrical. Although they are solitary animals, you may see many in one area. This may be because that spot is a good one for filter feeding worms, or that a lot of worm larvae landed there, riding on water currents.

Fans worms are found in most areas around the world, from shallow to deep depths. They live on coral reefs, rocks, sandy and muddy bottoms and small species can also live on boats, wharves, pontoons, water pipes, algae and seagrasses. Some species prefer dark spots on the under side of boulders, but many are found in brightly lit areas. After the larvae settle out of the water and begin to form a tube (or bury into a head of coral), they do not leave their tubes and can not move from place to place.

Fan worms are filter feeders. Their frilly tentacles are lined with cilia, which beat continuously to move water over the tentacles. Mucus on the tentacles trap small particles from the water which are passed down to the mouth (located in the middle of the tentacles) and eaten. Exactly what they eat depends on the species of worm: larger worms can trap and eat larger particles than smaller species. The smallest worms can filter and eat particles the size of bacteria.

Fish love to nip off the brightly coloured fan of tentacles, but they have to be fast! The worm's only method of protection against predation is to withdraw into its tube, and to close the opening with its hard door (operculum). But it can do this extremely fast! The front segments of their body (thorax) has strong muscles which retract the fan of tentacles at lightening speed. The tentacles themselves are sensitive to light, reacting to passing shadows. You can test this reaction by passing your hand above a fan worm and see how quickly it disappears.

Fan worms have separate sexes, but it is difficult to tell the difference between them without removing one from its tube. The egg and sperm (gametes) develop in the sac-like segments of the abdomen of the worm. The eggs appear orange or yellow and the sperm looks pale and creamy. They release eggs and sperm into the water in response to some trigger, such as warmer water temperature, longer daylight or phase of the moon. The eggs are fertilised in the water where the develop into a small top-shaped larva that swims and eats. The larvae are part of the planktonic community for some time, depending on the species, temperature of the water and the amount of food in the water. After they have grown to look more like a worm and have a few segments they settle out of the water and look for a suitable place to build a tube. Some species of fan worms brood their eggs in a gelatinous cocoon around the top part of their tube. The young that have been brooded spend little time, if any, floating in the plankton. Worms grow by adding segments to their body and extending their tubes. In fact, every time they extend their tentacles to feed they lengthen their tubes. Near the base of the fan of tentacles are two special glands that concentrate calcium from seawater. Calcium in these glands is mixed with a special kind of mucus and pasted on to the end of the tube to make it longer. Some species of young worms can add nearly a centimetre a month (during warm months) to their tubes, and broken tubes are repaired by the same method. Species that have a soft tube add to its length by pasting carefully selected sediment particles to the tube opening using a mucous secretion. Most small species of fan worm probably live less than two years, but larger species may live longer.

Some fan worms live only on heads of live corals. They settle on particular species of coral in a crack or crevice between polyps and make a tube. They can extend their tube as fast as the coral grows, so the coral cannot grow over them.

Large fan worms look nice in aquaria, but are difficult to collect due to their quick withdrawal into their tube at the first sign of disturbance. Corals collected for aquaria sometimes have commensal worms, but worms are not usually collected for the aquarium industry.

Because fan worm larvae spend some time in the plankton, they can be transported with the ballast water from ships across the seas. There is a species of fan worm that was introduced to several harbours in southern Australia in this way and has now taken over large stretches of habitat in those harbours.