The colorful set of trees in this picture actually belong to a single, lowly worm. Yes, believe it: It's a worm. This diminutive annelid (same phylum as earthworms) is a marine organisms and those swirling "branches" or radioles are the paired tentacles it uses for capturing food from the water. The spiral "trees" also helps with gas exchange.
As divers and snorkerlers will tell you, when disturbed, these whorls instantly retract and the worm pulls its door-like operculum closed behind it. Here's a Youtube video of some Christmas tree worms retracting.
Christmas tree worms take their common name from their appearance, of course. Their scientific classification tells us lots more about these animals. As annelids, they have segmented bodies. Segmentation was an important evolutionary step that allowed greater diversity in organisms' body plans. Digestive tracts could differentiate into separate parts, each with its own role: mouth and esophagus to bring food in and move it through the passage, crops, gizzards, and stomachs to store, grind and process food, intestines to absorb nutrients and water. Segmentation also lets organisms develop differentiated limbs. We see segmentation in humans through our vertebrae. Turns out, all organisms that exhibit segmentation share a similar gene, the Homeobox, or Hox gene, which serves as a molecular architect and directs the building of bodies according to definite detailed plans.
Our annelid, the Christmas Tree worm, belongs to the class of marine worms called polychaetes (along with fireworms), subclass sedentaria (along with feather duster worms, because they once the larvae settle, they secrete a parchment-like calcareous tube and then never move from that location), family serpulidae (this means creeping and probably refers to the larval stage. When ready to settle down, the larva creeps around a potential home in search of a good place to dig in.)
Spirobranchus come in a variety of bright colors, each worm with two "trees" poking out from its tube. Most often, they burrow into living coral, although sometimes they'll live in a rock or sponge, and secrete their tube.
S. giganteus possesses a complete digestive system and has a well-developed closed circulatory system. Like other annelids, they possess well-developed nervous systems with a central brain. They have fully developed nephridia simple kidneys) used for excretion. When they reproduce, they simply shed their gametes (eggs and spermatozoa) straight into the water and leave fertilization to chance and cooperative currents.
Christmas tree worms eat by capturing food from the plankton. "Capturing" sounds a bit more active than it really is. When currents carry tiny plants and animals floating in the water into the radiole, the tentacles direct that particle to the worms mouth. They don't really hunt anything down. Filter feeders wait for the food to come to them. They have few, if any, natural predators and no commercial value aside from as fascinating aquarium animals so they aren't endangered or threatened in and of themselves. With loss of their preferred habitat--coral reefs--their numbers could possibly decline, but for now, we get to easily and readily enjoy these colorful organisms while snorkeling and diving in tropical and subtropical waters worldwide.
Enjoy, and Merry Christmas, Happy Hannukah, Happy Kwanzaa, Merry Solstice, and a happy 2013!
Happy Holidays everyone!
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