In this session of relaxing minutes, we would like to introduce you to a critter that uses a flamboyant feature to mask what many people would deem an otherwise gross appearance. Yes, Sabellastarte spectabilis is, despite its beautiful name, not some fluffy plant or coral in a variation of colours, but in fact a humble worm. However, don’t let this little detail change your opinion of this creature. Sabellastarte does really make an effort to look more appealing than just another worm. As a matter of fact, another member of this family of worms, the Christmas tree worm (Spirobranchus corniculatus), was the inspiration for the beautiful Helicoradian plants on the moon Pandora, in the hit movie Avatar (2009).
Small, but beautiful: Feather Duster (Tube) Worm (Sabellastarte spectabilis)
Sabellastarte spectabilis has a segmented tubular body of around 8cm long, and roughly 1cm wide, and can be found in the more sheltered regions of the tropical reefs and lagoons around the world, ranging from 5-100m in depth. This worm creates a leathery-looking tube from its own mucus secretions and attached sediment and/or sand. Others use calcium carbonate or chitin, and some even have a trap door to close their tube off, in case of lurking danger. These tubes are then embedded, or attached to a variety of substrates, from where they compete with other organisms for food and space. Some even have the ability to physically, or chemically burrow into corals and/or limestone.
Eyes that no one sees
As a defence mechanism, these creatures are able to quickly retreat into their tubes, when disturbed by potential predators. It may come as a surprise, but Sabellastarte has eyes! And some species have more than others. They have multiple eyes along the sides of their bodies, as well as appendages called chaeta, which allow the worms to anchor themselves inside their tubes and aid in the retraction response. These eyes will likely let the worm know whether it’s still within the safety of its tube. Perhaps they might even locate areas of the tube that need maintenance. In some species, eyes may also be found on their heads and/or on the highly specialised, feather-like feeding tentacles, that stick out of the tube. That’s a lot of eyes for one creature!
While some of these eyes might simply detect light and darkness, others might be more complex compound eyes capable of producing a picture and detecting movement. Similar to that of more active predatory marine worms, or flying insects. Like many other sedentary life forms, Sabellastarte is a “filter feeder” that dines on planktonic prey and detritus brought in by the currents. They do this by using the only visible part of themselves, their beautiful exposed plumage. It is this plumage giving them the common name feather duster tube worm.
What makes Sabellastarte spectabilis a feather duster
Each feeding tentacle is called a radiole and is covered by feather-like pinnules and a sticky mucous, that form a fine mesh net, to capture any food particles that float by. Short vibrating microscopic hair-like structures, called cilia, cover both the radiole and the pinnules. Cilia can also be found in humans, where it lines our lung surface and windpipe, and capture and remove dirt particles and mucous. Vibrating cilia on the ventral surface (underside) will create an up-current, directing particles through the radiole and pinnules, where they can be caught.
From there, a decrease in pressure makes the particles fall into the ciliated groves on the dorsal (upper) side of the pinnule, from where they will be transported via several other ciliated, mucous-lined food grooves down to the actual mouth. There the particles will be sorted. The edibles will continue their journey into the worm itself, the rejected particles will be removed via other ciliated grooves away from the mouth. Some of these particles will be stored, and used for repairs on the actual tube when it has sustained damage.
Lizard-like distraction by Feather Duster (Tube) Worm (Sabellastarte spectabilis)
In addition to all that, the large surface area of the plumage also acts as gills, making them technically known as branchiae, since they’re used for respiration. With so many important functions located in a small area, one would think that if a predator was quick enough to bite a chunk of the plumage, the worm would surely die. But sabellastarte has the uncanny ability to regenerate damaged or lost body parts! Several species have shown to be able to control the loss of the crown of tentacles, a process known as autotomy. Lizards have a similar process whereby they intentionally lose a tail in order to distract a predator and enable their escape.
They reproduce by spawning, releasing eggs and spermatozoa in the water column in the hope that they will find one another before any predator, including themselves, get to them. Strangely enough, Sabellastarte is also capable of reproduction by fragmentation, also known as „budding“. So you see, there’s a very interesting creature hiding behind those colourful plumes!