Bispira viola

Acclimation: never lift the worm out of the water, as air can get trapped in its tube; move it in a bag, under water. When buying, pick a specimen with a complete crown that withdraws briskly when touched, and whose tube is neither torn nor broken. Invertebrates cope poorly with changes in water quality: bring the bag water to your tank's water slowly.

Setup: it usually arrives by itself with live rock and settles high up, on rocks and algae. A tank of at least 50 litres is enough. Nothing special is needed beyond a current that brings particles; a population boom reflects a tank rich in suspended matter.

Tankmates: these worms do not sting, do not eat other animals and do not compete with them chemically. The reverse is not true: butterflyfish relish their crowns, some wrasses and hawkfish eat them, as do triggerfish, large puffers, filefish and some angelfish; omnivorous crabs kill them by pinching the tube, and eels or urchins can damage them as they move about.

Crown loss: many feather dusters shed their crown from time to time. Do not remove the tube: the crown grows back within a few weeks. An occasional loss is nothing to worry about; if it happens every couple of months, look for an irritant or a lack of food. A starving worm drops its crown and grows a smaller one each time, so a shrinking crown means it is not getting enough food. Invertebrates do not tolerate copper medications.