WHAT’S THE DIFFERENCE BETWEEN FEATHER DUSTER AND CHRISTMAS TREE WORMS? For one thing, the conical feathery crowns of Christmas tree worms shout out their presence with color and beguiling shapes. Feather dusters’ fan-shaped crowns often whisper with subtle elegance.
If it’s simply about appreciating the beauty of the reef, that’s the main point – conical versus fan-shaped, bold versus muted. It’s the fan shape that gives feather dusters their other common name, fan worms.
Christmas trees present dramatic sights in shades of oranges, rusty reds, yellows, whites, blues, browns and tans. There are dramatically colored feather dusters, but mostly they’re more muted. Yet a colony of pure white or reddish brown social feather dusters displays an elegant beauty.
SIMILARITIES BETWEEN FEATHER DUSTER AND CHRISTMAS TREE WORMS
Feather dusters and Christmas trees are both sessile tube worms – that is, they spend their lives fixed in holes in coral masses or sandy seafloors. They’re both members of Phylum Annelida, Class Polychaeta, worms with bodies of ring-like segments, although they’re in different families (Christmas trees: Serpulidae; feather duster: Sabellidae).
They both extend their paired crowns of some 30 feathery radioles into the water column to breathe and to filter plankton, passing it down to their mouths at the crown base. Rather than wait passively for plankton to pass by, they can wave their feathers to create a mile flow of water that brings their tiny prey to them. Coated with sticky mucus, the radioles trap any particle that contact them.
But Christmas trees, members of species Spirobranchus giganteus, are pretty much entirely found in embedded in corals. Feather dusters may be just as happy on a sandy bottom. S. giganteus builds its protective tubes of calcium they secrete as the coral builds up around them. Feather dusters, in many genuses and species, create parchment-like tubes of mucus, strengthened with bits of sand and shell. One genus of feather dusters, does create its tubes with calcium carbonate.
For both feather duster and Christmas tree worms, those feathery whorls of gills are also attractive to predators hoping to pick off an easy snack, so the ability to quickly withdraw into a protective tube home is important the worms’ survival. Christmas trees have the advantage of opercula, or trap doors, they can snap shut above them, flush with the coral surface.
Feather dusters lack this, and in fact their tubes often extend above the substrate, even when they have withdrawn into it. Still, they find safety in their retreats.
CROWD SOURCING – OR NOT
If Christmas trees are often found bunched together, it suggests that the conditions are attractive for their settlement there as larvae, and it makes for efficient broadcast spawning. But they’re still individuals who may be closely packed or spread sparsely on coral surfaces, often displaying an array of hues. And they’re S. giganteus, regardless of the colors of their canopies.
Some species of feather dusters seem to be determined loners. But members of the Caribbean species Bispira brunnea are socialites – okay, social feather dusters. They gaggle together in solidarity and uniform coloration.
BEHIND FEATHER DUSTER AND CHRISTMAS TREE WORMS’ PLUMES
Like land-based earthworms, as polychaetes feather duster and Christmas tree worms sport bodies of ring-like segments. While a central gut runs through a polychaete’s body, each segment features parapodia – appendages sort of like undeveloped feet. Extending off them are setae, in many cases best described as bristles (the bristleworm, or fireworm, is a free-ranging polychaete).
As tubeworms, the mucus they secrete helps them slide up and down their tubes.
Both groups of worms reproduce through broadcast spawning. And, they’re apparently picky about what kinds of corals they settle on. Biologists know that but they’re still trying to figure out what the criteria are. One suggestion is that they try to avoid corals frequented by algae-eating parrotfishes, which tend to scrape away the corals and anything else in their way while ferreting out algae.
FAN WORMS’ FANTASTIC EYES
Recent research has focused on feather dusters’ remarkable visual capabilities. As a team of Swedish and Norwegian researchers put it in a paper titled “Here, There and Everywhere: The Radiolar Eyes of Fan Worms (Annelida, Sabellidae), fan worms “possess some of the strangest eyes in nature… They display a surprising diversity of eyes of varying levels of sophistication, ranging from scattered single ocelli to compound eyes with up to hundreds of facets.”
Since their primary polychaete eyes are unfortunately stuck inside their tubes most of the time, various species have evolved additional eyes all over the place, including on their radioles. While some are simple light-detecting ocelli, some are resemble arthropod compound eyes, sometimes with vertebrate-like characteristics.
PRINCIPAL SOURCES: Marine Biology, Fourth Edition, Peter Castro, Michael Huber; Reef Creature Identification, Florida, Caribbean, Bahamas/Reef Creature Identification, Tropical Pacific, Paul Humann, Ned DeLoach; “Feather Duster Worm,” Marine Education Society of Australasia; “Featherduster Worms,” Waikiki Aquarium; “Here, There and Everywhere: The Radiolar Eyes of Fan Worms (Annelida, Sabellidae),” Integrative and Comparative Biology; “Fanworms, ’Nature’s Eye Factories,’ Stick Them Pretty Much Anywhere,” Scientific American; “Sebellidae,” Wikipedia.