Multi – Bristled Worm
This species, which belongs to the Serpulidae family, is one of the most beautiful and colorful reef inhabitants.
The world’s coral reefs are characterized by the many Christmas-tree worm colors, blue, yellow, orange, purple, brown, red, among others.
They are very different to the other bushy and especially lumpy coral species such as hump coral, cyphastrea, flower coral and coelenterata. The worms get their color from their feathery spirals (protruding tentacle type organs with a concentration of sensory cells). The Christmas-tree worm does not drill, or dig holes in the coral’s skeleton, it settles on the coral’s living tissue cells, building a calciferous pouch framework on the coral.
Its body is encased in the protective pouch, and the feathery spirals either extend outwards, or retract into their opening. The coral, which is constantly building its skeleton, usually covers most of the pouch, leaving only a small exposed opening as a connection to the surrounding waters.
This opening is used for nutrition, respiration, and for the release of reproductive substance in to the water. The worm has to preserve its pouch structure and growth rate to prevent the opening from being covered, and blocked by the coral skeleton. After its death, the opening becomes completely covered by the coral skeleton.
This species grows to a size of 5 – 6 cm.
The feathery spirals are shaped with two coiled funnels resembling a Christmas tree, one against the other.
Contrary to the heads of common worms, located in the front section of their bodies, the degeneration of the head in these types of worms caused the development of fan-like filters which are used to collect food. The worm’s nutrition is based on filtering the organic food particles in the water. The filter process is performed by the deliberate movement of the lashes located on the tentacle filter. The movement of the lashes causes the water to flow through the tentacle, and the trapped particles are transported towards the mouth. The movement of the lashes even allows the reflow of “fresh” oxygen enriched water required for the respiratory process.
Any sudden change in lighting such as a shadow causes the worm to immediately retract into its pouch, and its colorful tentacles to disappear.
Its ability to retract with speed, and close the pouch cover was developed as a protection mechanism against predators.
Christmas-Tree Worm Reciprocity
It is essential for these worms to settle on coral; however, the same is not true for the coral. Sitting on top of a living bed such as coral gives the worm an advantage in terms of its competition with other animals for space and food. Even though the worms do not drill into the coral’s skeleton, to some degree, they do create spaces in the skeleton which could weaken its resistance during storms. On the other hand, the flow of water through the spiral tentacles amplifies the hydrological cycle around the coral, which brings additional food particles to its polyps.