When people think of Christmas animals, reindeer usually come to mind first, and the next thoughts are often of a pear-tree dwelling partridge, camels, the Yule goat, French hens or a mouse who was among the creatures not even stirring when it ‘twas the night before. It’s time to move beyond these traditional animals to make way for a modern animal of the season whose name comes from its festive appearance. I refer, naturally, to the Christmas tree worm.

The Christmas tree worm is a member of the polychaetes, a group of segmented worms containing over 13,000 species that are collectively known by the common name “bristle worms”. These worms are marine animals related to feather duster worms and beard worms, and they owe their name to the brightly colored crowns or plumes that protrude from their otherwise tube-shaped bodies. The tube is about two-thirds of the length of their body, but is usually hidden within coral, as these animals make their home in cavities that they excavate in hard underwater surfaces.

Each individual Christmas tree worm has two crowns, which come in many colors: orange, blue, white, yellow and red. Despite the range of colors, all Christmas tree worms are members of the same species, Spirobranchus giganteus. The crowns are used for feeding and respiration. The worms can pump water over these structures, which are sticky and full of bristles, allowing them to trap bits of plants, animals or debris to eat. They also gather oxygen with their crowns.

Christmas tree worms are delicate, beautiful and quite small—about an inch-and-a-half in height. They usually live for 10-20 years, though reaching the age of 30 is possible. Found in tropical oceans at depths from 10 to 100 feet, they are among the best-known and most widely recognized of the segmented worms, perhaps only second to earthworms in this regard.

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Because Christmas tree worms are sedentary, meeting a worm who is Mr. or Ms. Right is impossible. Instead of meeting and courting, these animals discharge their gametes directly into the water. Males time the release of their sperm to match the release of eggs by females. Fertilized eggs drift in ocean currents and develop into larvae while they are on the move. When they come upon a coral head, the young worms settle there and begin to burrow, creating their distinctive tubes.

If disturbed by a passing shadow or by even the lightest touch, Christmas tree worms immediately retract their crowns into their tubes. In a minute or two, they will begin to emerge very slowly to test out the situation before fully extending the body once again.

Due to their great beauty, including their vibrant colors, Christmas tree worms are very popular with underwater photographers who must dive beneath the ocean surface and use expensive waterproof gear to photograph them. Even with those inconveniences, it is much easier to get a stunning picture of these worms than to capture one of the typical human family during the holiday season.

Karen B. London, Ph.D. is a Certified Applied Animal Behaviorist, Certified Professional Dog Trainer, author, and an Adjunct Faculty in NAU’s Department of Biological Sciences.

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