Christmas tree worms are typical sedentary filter feeders which strain food out of the water column by circulating it through its system.
Their body is usually hidden inside its tube until the spiral Christmas tree shaped crown projects from the burrow to feed.
The crown contains multiple radioles which have fan-like cilia branches.
Cilia are tiny hair-like organelles and each cilium is used for respiration and primarily for feeding.
The worms depend on the cilia appendages and water currents to guide their diet of suspended food particles towards their mouth or digestive tract.
Like most tube worms, Christmas tree worms need sustained healthy feeding to survive. Most of the larger species eat ciliates, organic detritus, and certain types of invertebrate larvae, such as zooplankton and phytoplankton.
The Christmas tree worm's most common predators are crabs and shrimps and there is strong evidence that sea urchins also chew on Sabellid tubes.
Some large tropical reef fish also eat Christmas tree worms. Using its elongated proboscis, the beautiful butterfly fish (Chaetodontidae) regularly diets on the worm's spiraling plumes.
If not completely eaten, missing or damaged tentacles usually regrow after a few weeks.
Christmas tree worm's change their habitat after the end of the larval life-span. This can be only a few hours or more than a week following birth. The type of coral habitat they select for living correlates to their overall size and ongoing reproductive success at maturity.
In simple terms, more gametes are produced by larger marine worms. Colony densities vary because they are selective about choosing the location for the new habitat.
Spirobranchus colonies might be only a few worms per coral head or there are reports of staggering densities reaching over 100 worms per square meter.
Polychaetes construct calcareous homes that provide a relatively permanent shelter for each individual Christmas tree worm. They remain inside this tubular habitat throughout their adulthood lives.
S. giganteus have developed an operculum which is a defensive cover or lid which plugs the top of their tube when they retract inside. When the Christmas tree worm dies the vacant serpulid pipe creates a domain for other animals.
Very often you will find a coral hermit crab or a small goby or blennie living inside the spent funnel of the dead marine worm.
Christmas tree worms and coral shares obligate benefits (symbiosis). The tube-dwelling worm does not need the coral for food but benefits from a secure locate to build secure habitat.
Nevertheless, even if the coral dies, the marine worm can live independently. There is a suggestion that coral reefs benefit from harboring colonies of Spirobranchus worms because they irritate the stomachs of crown-of-thorns sea stars, discouraging the sea star from consuming huge swaths of porites.
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