One of my favorite activities while scuba diving or snorkeling on a tropical reef is to gently approach a coral rock and observe the colorful Christmas tree worms without startling them.
These tiny creatures resemble miniature fir trees, resembling the man-made variety made of brightly colored plastic and tinsel. They come in a variety of colors such as red, yellow, orange, and blue, but they all belong to the same species, Spirobranchis giganteus.
If you get too close, these reclusive creatures quickly retreat into a tube in the coral, closing the small gill opercula behind them before eventually reemerging when it’s safe.
Christmas tree worms can grow up to 3.5 cm in length, with most of their bodies concealed within the tube. They have feather-like spiral tentacles known as radiozoa that are used for breathing and feeding.
These tentacles, which act as gills, absorb oxygen and filter out food particles and plankton, transporting them towards the worm’s mouth. Close relatives of Christmas tree worms, including feather dusters and peacock worms, are part of the same family, Sabellidae.
Both female and male Christmas tree worms release their eggs and sperm into the seawater, where they fuse to form larvae that drift for 9-12 days before settling on a suitable coral to begin their lives. These worms are known to be picky about their coral hosts and can live up to 30 years.
Christmas tree worms have hundreds of bright orange eye spots between their tentacles, which contain light-sensitive opsin pigments that send signals to the worm’s brain to alert them to potential predators overhead. Interestingly, worms in crowded colonies tend to hide in their nests for longer periods of time, possibly due to the safety of blending in with a larger group.
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Source: www.sciencefocus.com
