These animals feed on copepods, diatoms and particles collected on coral mucus. Their brown colour is due to symbiotic algae.

Like many other animals they are unintentionally introduced on corals and live rock and do not normally cause any problems. However if they reach plague proportions they can smother everything in the tank, depriving other animals of oxygen.

It is possible to syphon them out but this is often a never ending job as they seem to return in increasing numbers. A more certain method is to introduce one or more Chelidonura varians nudibranchs. These beautiful little black slugs with bright blue lines eat the worms but as they are specific feeders they will die after clearing the tank of their food source.