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Christmas Tree Worms

by | Nov 18, 2021 | 0 comments

Under a flaming sky, crimson and azure blended to form the endless undulations of the Coral Sea. As the dawn grew brighter, the crimson rippled into scarlet, and the scarlet faded into orange. Suddenly a gleaming orb topped the horizon, and the world was transformed. Golden diamonds seemed to dance over the sapphire waves. A new day had begun.

Out on the sea, new life had begun. In the early hours of the morning, a tiny egg had hatched and released a wriggling Christmas tree worm. In its larval state, the worm looked nothing like a fir tree. Before the transformation to an adult, the larva would ride the waves, filling itself with plankton. If conditions were ideal, this stage might only last several hours. However, it could take a few weeks before the worm was grown enough to settle on a coral and metamorphose into a benthos juvenile.

Within a day, this particular young worm began the search for the perfect coral. This decision was an important one, for the worm would remain on the coral for its entire life. This could be the average lifespan of ten to twenty years or as long as forty years.

It was hard to say what the worm was considering, but it eventually settled in a crevice of a large wrinkled brain coral. Several dozen other worms had already taken up residence there, some so long ago that the coral had grown over their tube-like homes. A nearby giant clam housed yet another Christmas tree worm.

Here on this coral, a great transformation occurred. The worm changed into a juvenile, the stage between larva and adult. Around the juvenile, a mucous tube formed, forerunner of the permanent calcium carbonate tube the adult would live in. The juvenile worm took on the form of the adult and acquired the twin, tree-shaped crowns that give it its name.

These crowns were interesting affairs. Around their short stalks spiraled thin, frilly radioles, or tentacles. The worm drew the water up through the radioles, filtering out plankton and oxygen. Sand and shell fragments were also ingested, processed in a special gland, and used to build the worm’s hard tube.

The crowns’ most intriguing aspect, however, was their coloration. There were nearly as many colors as worms, though both crowns in a pair were identical. Several worms were solid-colored, but many were tipped, fringed, spotted, striped, or swirled with a second color. The most ornate of the worms wore several colors. This particular worm swirled an array of red, white, and green from a candy-cane-striped stalk. In coral reefs across the world, several dozen Christmas tree worm species display every color of the rainbow.

Nestled down inside the crown were the eyes of the Christmas tree worm. This position meant that the worm could only see directly forward and backward. But the worm could sense water movement and, with special cells in his radioles, changes in lighting. At the least disturbance, the worm shot back into its tube. Like many Christmas tree worms, he built his tube longer than his one-and-a-half-inch body to allow him to retract farther inside.

His defenses didn’t stop there. Closing the hole into which the worm withdrew was a covering called an operculum. From the operculum rose a set of antler-shaped spines, defying any fish to push its way in. While the worm’s crowns were outside its tube, the operculum rested to the side, its color adding to the display.

A shadow drifted over the reef, and the Christmas tree worm detected a slight current in the water. Faster than you could say, “Blue-cheeked butterflyfish,” all that could be seen of the worm was a spiny cover on a hard tube. The neighboring worms had been nearly as quick in their response to the intruder, and the butterflyfish was left with no trace of a meal.

This butterflyfish was wise in the ways of Christmas tree worms, however, and he continued to hover near the worm’s tube. His patience was rewarded when, a good minute later, the crown of the worm began to swirl out. The worm paused to test the water. He had just concluded that life was back to normal and had begun to fully extract himself…

BAM! The Christmas tree worm retracted, but this time he moved too slowly. When the butterflyfish drifted off, he carried a fragment of the worm’s radioles in his mouth.

The worm sighed. The piece of crown would grow back; he had only a minor injury. But those exasperating butterflyfish were everywhere! This time he waited a full two minutes before slowly reemerging.

As he did so, the spines on his operculum scratched the coral, exposing it to the harmful filamentous algae dotting his hard exterior. But the worm’s presence was not entirely harmful to the coral. Later that day, he joined several other Christmas tree worms in chasing away a coral-eating crown-of-thorns starfish. The starfish, unhappy with his discourteous reception, left the coral in peace.

Across the world, in a reef near the Florida Keys, another Christmas tree worm had a fishy problem. But this fish, a tiny peppermint goby, had no desire to disturb the worm. Rather, he swam down through the tentacles in search of food that the worm had missed. The goby moved so smoothly that it was some time before the worm detected its presence and retracted. Unfazed, the kleptoparasite simply moved on to the next worm to practice his food stealing.

•••

The horizon was engulfed in a blaze of color as the sun sedately sank beneath the tranquil Coral Sea. Far beneath the surface, Christmas tree worms again swirled out their lacy crowns. But this time, one was missing. A butterflyfish, topping off his supper, had struck successfully this time.

A young hermit crab swam toward the coral, searching for a home of its own. Its expressionless eyes picked out the recently vacated tube of a Christmas tree worm. Slowly it approached, examining the area. Satisfied with its surroundings, the crab entered the spacious fortress and settled down to stay. Life would continue in the home of the Christmas tree worm.

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