Christmas Tree Worm

Spirobranchus giganteus

It is difficult not to become intrigued with these fascinating creatures called Christmas tree worms. These structures come in wide variety of hues and patterns. Indeed a field of these brings to mind a tropical  fiesta.

christmas-tree-worm

The twin spiral whorls are in fact the organism’s highly modified respiratory and feeding apparatus. These structures are part of the worm’s mouth. The twin spirals are composed of tentacles (called radioles) lined with tiny hairs called cilia. It is these hairs that trap food material in the water and then passes it down into the worm’s waiting mouth. The worm, through the movement of the tentacles, can actually sort through the material it traps. Larger particles like sand particles are discarded while smaller ones are led down into the worm’s digestive tract. The feathery tentacles themselves are involved in exchanging gas with the water around the worm, their version of breathing.

Christmas tree worms are Polychaetes and belong to the family Serpulidae also known as the tube worms. Any disturbance would lead these highly sensitive creatures to withdraw their spiral plumes into their tube-like body. The light sensitive tentacles can even detect subtle changes in light, as when a diver or snorkeler swims just above the worm’s location. Divers and photographers need to approach them carefully and slow, and  minimize their movement in order to avoid short-lived encounters with these fascinating creatures. As the worm registers the disturbance, it pulls in its tentacles and plugs its opening with a lid-like structure called an operculum. When they do reel in their beautiful plumes, it pays to stick around for a couple of minutes and wait  for the plumes to slowly, tentatively, re-emerge.

They are found in coral reefs, usually on the surface of coral themselves. Larvae typically settle on the coral surface, burrowing and extending their tube-like bodies into the hole. The worm uses calcium from the environment to fortify its tube. As the coral grows around them, they become embedded deeper into the structure. Christmas tree worms are usually found in stony and brain coral surfaces. The twin cone shaped structures are usually about 1-2 cm in length though most of the worm’s body is in fact deep within the coral and may reach a full length of  4 cm. Male and female Christmas tree worms release sex cells into the water, where fertilization occurs. The larvae then drifts down to the coral surface to begin a new, colorful life among the reef’s denizens.

Christmas tree worms can be found on many hard corals in most dive spots in Dauin and Apo Island.