Spirobranchus giganteus: Real Life Christmas Trees!

Although a bit belated, in the spirit of Christmas I would like to introduce you to a really cool animal the existence of which I learned today. First let's have a look:

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And another:

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Although they look like some kind of marine plant, I assure you..these things are actually animals! Scientifically described as Spirobranchus giganteus and commonly known as Christmas tree worms, these creatures are tube-building polychaete worms from the family Serpulidae. As you can see in the photos, they are named this way due to their appearance and not because they eat Christmas trees or something! 

They come in a variety of bright colors and don't get to be very big, about 4-5 cm long and occur throughout the world's tropical oceans from the Caribbean to the Indo-Pacific. They are usually embedded in corals and despite their small size they are easy to spot thanks to their distinctive appearance and bright colors.

 As for the name "Spirobranchus", it essentially translates to "spiral gills," referring to the worm's two unique crowns. These crowns are used both for catching food and respiration:

These are highly modified prostomialpalps, which are specialized mouth appendages. Each spiral is composed of feather-like tentacles called radioles, which are heavily ciliated and cause any prey trapped in them to be transported to the worm's mouth. While they are primarily feeding structures, S. giganteus also uses its radioles for respiration; hence, the structures commonly are called gills. [source]

Their diet consists of small stuff, mainly microscopic plants (phytoplankton) that floats in the water. As for enemies, like with all tube-borne polychaetes, there are very few animals that feed on them, for example the Grapsus grapsus crab.

Despite their looks, these animals are way more complex than you might think and come with a fully developed nervous, circulatory and digestive system:

As an annelid, S. giganteus possesses a complete digestive system and has a well-developed closed circulatory system. Like other annelids, these worms possess well-developed nervous systems with a central brain and many supporting ganglia, including pedal ganglia, unique to the Polychaeta. Like other polychaetes, S. giganteus excrete with fully developed nephridia. When they reproduce, they simply shed their gametes straight into the water where the eggs (and spermatozoa) become part of the zooplankton to be carried by the currents. [source]

Like other polychaete worms, christmas tree worms can also secrete a calcareous tube around their body which acts like their "home" and offers them protection. Usually the tube is made inside a living coral for further protection.  If all goes well they will just stay there for the rest of their life.

By the way, the colorful crowns you see in the photos are only a small part of their body, most of it stays inside the tube and if they feel threatened by a predator (or a curious human) they can retract that too.

In case you wonder, the species is not threatened and is actually a pretty common sight.

There's not much else interesting too say about these beautiful creatures without getting too much technical so I will leave you with some more cool photos and videos:

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More Strange Animal Stuff  

If you enjoyed reading  this post I am sure you will love some of my previous posts:

• 3 Amazing Spiders That Pretend To Be Something Else!
• Giant Isopods - Aliens Of The Deep
• 3 Creepy Critters I Discovered This Week + Baby Bat Burritos
• Clathrus archeri: Weird Alien-Like Eggs Hatch Into Weird Octopus Thing
• The Horseshoe Crab Named After Darth Vader
• Lobster with Pepsi Tattoo Fished In Canada !
• The Jesus Christ Lizard: A Lizard That Can "Walk" On Water
• It's a Scorpion...It's a Fly...It's a Scorpionfly! (Panorpa communis)