Christmas tree worms are polychaetes of the genus, Spirobranchus (Serpulidae). These reef- dwelling species live inside tubes that are usually embedded inside the skeletons of corals belonging to either the order Scleractinia (Anthozoa) or to the family Milleporidae (Hydrozoa) (Hoeksema and Ten Hove 2017, Perry et al. 2017). Extended Spirobranchus worms are visible because of their large, bright-colored branchiae, shaped as twin spirals, and a peduncle (stalk) with a calcified spiny operculum on top. Their colormorph variation and the presence of long spines on the tube may serve as protection against predators (Grassle 1973). When in danger, the worms are able to retract quickly inside their tube, while using their operculum as a shield (Hoeksema et al. 2016, Pezner et al. 2017).
Although little is known about predators of Spirobranchus spp. and no actual attacks have been documented (Kupriyanova et al. 2001), predation has been inferred from damaged and/or missing opercula in about 10% of the examined specimens [Nishi and Kikuchi 1996 for Spirobranchus corniculatus (Grube, 1862)].