Christmas tree worms (Spirobranchus giganteus) are tiny little animals of about 1.5 cm length that live inside corals and giant clams for their entire life. These worms are sessile organisms that produce a calcium carbonate tube in which they can fully retract when threatened. Their body is characterized by bright colored feather-like tentacles, called radioles, used both to breathe and to eat.

Indeed, these worms are filter-feeder organisms, meaning that they catch food by filter particles and microorganisms present in the surrounding waters and carry them into the mouth through the movement of cilia and mucus.