On Chek Jawa, fan worms are found mainly in the coral rubble area. Those that remain in a pool of water at low tide will have their feathery fans unfurled. There are large ones (about 8cm in diameter), small ones (2-3cm in diameter) and even tinier ones that can hardly be seen.

Fantastic Fan: A fan worm is a segmented worm. It has a marvellous feathery fan on its head! Each long 'feather' of the fan is actually a modified tentacle called a radiole. Each radiole has many pinnules (feathery branches). Each pinnule is covered with cilia (tiny beating hairs).

The cilia generate a current, sucking water from below the fan, through the pinnules and out through the centre of the fan (indicated by the blue arrows). Cilia on the pinnules gather tiny food particles from the current and send these to a groove along the length of each radiole. Cilia in the groove sort out food particles by size as they bring these particles to the central mouth. A pair of palps near the mouth removes particles which are too large: cilia on the palps carry these particles to the centre of the fan and toss them into the outgoing current. Only suitably small particles are eaten.

Down the Tubes: Fan worms live in a flexible, leathery tube. The tube is often much longer than the worm. Some fan worms have eye spots on their tentacles to detect movement. Fan worms will slip instantly into their tubes at the slightest sign of danger. The tubes also keep them moist and safe on the rare occasions when they are exposed at low tide.

Fan worms don't have an operculum to close off their tube entrance. Instead, when they retreat into their soft tube, the tube entrance collapses to seal the opening.

How does a fan worm make its tube? Sand grains of suitable size are collected and stored in a sac. The sand is mixed with mucus and extruded as a string of tube material. The worm rotates its body to apply this string to the tube, to lengthen or repair it. It moulds the string with a special fleshy fold of tissue near the top of its body (which looks like a shirt collar), almost like building a pot out of clay ropes.

Human uses: Fan worms are popular in the live aquarium trade and collected for this purpose.

Status and threats: A fan worm (Sabella spallanzanii) introduced to Australian harbours and coasts is affecting some mussel farms because they grow on the lines meant for mussel larvae settlement. Dense growths of these worms foul up dredges and nets, overgrow seagrass and are such effective filter feeders that they deprive native filter feeders of food.