Oh Christmas tree (worm), oh Christmas tree (worm), how functional are your branches! Christmas tree worms (Spirobranchus giganteus), found throughout the tropical waters in the Indo-Pacific and Caribbean, are segmented worms that inhabit coral reefs. They use their colored, spiral fans (that give them their festive name) for feeding and respiration. When threatened, they can quickly retreat into calcareous tubes of their own making, complete with an operculum (read: trap door). 

Sketch and fact contributed by Karli Chudeau

Source: Hoover, J. P. (1999). Hawai’i’s Sea Creatures: A Guide to Hawai’i’s Marine Invertebrates. Honolulu, HI: Mutual Publishing.