In our last column, (Lovely Worms – Spotlight on the Fire Worm) we introduced the predatory Fire Worm, one of 8,000 or more species of marine worms found throughout the world. While the Fire Worm moves about freely and is quite beautiful, two more marine worms, even more beautiful and frequently seen, are not mobile due to a lack of appendages designed for movement. The Christmas Tree Worms and Feather Duster Worms are tubeworms living their entire adult lives in one spot attached to various coral species.
Tubeworms reproduce by discharging eggs and sperm into the surrounding water where fertilization takes place. The resultant larvae are carried by currents as a component of plankton. Those that are not consumed by plankton feeders settle upon coral. Once settled, most tubeworms burrow into the coral creating a foundation for building their tubes. Their tannish-grey tubes are made of calcium secreted by the worm. Some tubeworms have specialized sacs into which they separate grains of sand and bits of shell filtered from the water. This mixture is added to their calcareous secretions.
Rarely if ever are the actual tubeworms seen as the head and main body remain within the tube. What we do see is an evolutionary wonder. How does a worm that cannot move and remains throughout its lifetime encased in a tube manage to breathe and feed?
As a diver, I never cease to smile when I find Christmas Tree Worms. Shaped like a Christmas tree in colors of white, red, blue, pink, orange, brown, maroon or yellow, the little worms bring about a myriad of happy reactions among divers and snorkelers. At approximately an inch-and-a-half in height, they are one of my favorite creatures to show new divers.
What we see of the Christmas Tree Worms are the palps, also known as crowns, leading to their mouths. Each worm has two spiral cone shaped crowns. Radioles, feathery plumes, extend from the center spine of the crowns giving them their Christmas tree shape. These multipurpose radioles serve as the worm’s breathing apparatus as well as passively snagging food, phytoplankton, which is then carried down the crown into the worm’s mouth by tiny moving hairs called cilia.
Cousin to the Christmas Tree Worm is the Feather Duster Worm, named after ostrich feather dusters due to their strong resemblance. Up to ten or more inches tall with radiole diameters of up to seven to eight inches, Feather Duster Worms are found in clusters as well as individually. Their color range includes white, brown, gray, pink, orange, red, and purple often with variegated striping. Feather Duster Worms have only one flattened crown from which two fans of equal length radioles extend.
Unlike the passive feeding Christmas Tree Worms, Feather Duster Worms move their radioles to create a current directed toward the worm’s mouth. Additionally, the radioles are covered in a sticky mucous like substance to which the plankton sticks giving this tube worm extra assistance when feeding.
Like the Christmas Tree Worms, some species of Feather Duster Worms discharge eggs and sperm into the water; however, depending upon the species they may also deposit eggs in a gelatinous mass along the tube from which the eggs eventually break loose and disperse in currents.
Christmas Tree Worms and Feather Duster Worms are easily disturbed. When disturbed, the radioles quickly withdraw into the tube and the worm’s operculum, hatch, shuts protecting the soft, defenseless worm. If left undisturbed, the operculum opens and the radiole slowly reappears. During times of stress, when plankton is scarce or water quality poor, both these tubeworm species can shed their radioles and regenerate new ones as conditions improve.
These two species of tubeworms can live in water as shallow as a few feet up to depths of approximately 100 feet. Christmas Tree Worms are found mainly on coral while the commonly seen Feather Duster Worms are found amongst corals as well as at the base of reefs. Because these tubeworms require plankton carried by currents to survive, they will not be found in areas of still water nor will they be found in areas heavily populated by sea urchins, one of their primary predators.