Christmas Tree Worm

Spirobranchus giganteus, commonly known as the Christmas tree worm, is a polychaete worm in the family Serpulidae, formally described by Pallas in 1766 and named for its two spiral, tree shaped crowns; its genus name translates roughly to spiral gill. It inhabits coral reef environments across the Caribbean and Indo-Pacific, living embedded in coral heads, particularly stony corals such as Porites and brain corals, where it secretes a calcareous tube up to twenty centimetres long. The worm measures about three and a half centimetres in body length and is best known for its paired crowns, which are actually highly modified mouth appendages called prostomial palps bearing feather-like tentacles used for both feeding and breathing; it seals its tube with a plug called an operculum, formed from a modified radiole, when threatened. As a sedentary filter feeder it draws microorganisms from passing water currents, and though it has no commercial importance, its vivid colouring makes it a favourite subject for divers and aquarium enthusiasts.