Christmas Tree Worm (Spirobranchus giganteus)
S. giganteus, like other members of its family, possess a modified radiole, usually called the operculum, that it uses to secure its hole when withdrawn into its tube.
As an annelid, S. giganteus possesses a complete digestive system and has a well-developed closed circulatory system. Like other annelids, these worms possess well-developed nervous systems with a central brain and many supporting ganglia, including pedal ganglia, unique to the Polychaeta.
Like other polychaetes, S. giganteus excrete fully developed nephridia. When they reproduce, they simply shed their gametes straight into the water where the eggs (and spermatozoa) become part of the zooplankton to be carried by the currents.