A Christmas Tree Worm (Spirobranchus giganteus) buried within Brain Coral (Diploria strigose) extends its two “crowns” 45 feet below the surface of the Gulf of Mexico off the coast of Riviera Maya. Christmas tree worms are widely distributed throughout the world's tropical oceans, residing from the Caribbean to the Indo-Pacific. The two Christmas tree-shaped multicolored spiral “crowns” per worm that protrude from the tube-like body are mouth appendages highly specialized for both feeding and respiration. These animals possess a complete digestive system, a well-developed closed circulatory system, and a nervous system with a central brain and many supporting ganglia. The worms have two eyes that can detect light which are tucked under the crowns. The eyes can be partially seen in this image as two brighter red oblong structures between the crowns at their base. These adaptations allow Christmas tree worms to rapidly retract their crowns into their burrows at any sign of danger. Interestingly, the nerves from these eyes do not go to the usual section of the brain associated with vision, and the light-sensitive proteins in the eyes called opsins are not the typical eye variety. Christmas tree worms come in a wide variety of bright colors and are generally about 1.5 inches (3.8 cm) in length.
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