The distinguishing characteristic of all annelids is the fact that they are made up of multiple segmented rings. In fact, their name comes from the Greek word for little rings, annelus. 

 

Candidate: Spirobranchus giganteus

 

The Annelids, despite only consisting of about 22,000 extant species, show a truly remarkable variation in shape and size. S.giganteus belongs to the class polychaeta, meaning it has several appendages called chaetae on each of its segments. This species is affectionately known as the “Christmas-tree worm” due to the fact that it has two large appendages coming out of its side which spiral up to a point and therefore resemble a christmas tree. The worm is able to build specialised tubes on the surface of corals which they are permanently retreated into. Not only does this Annelid have a beautiful shape, it also can display a variety of different colours depending on the colours of the coral reef in which it is located. I’ve seen bright blues, deep purples, oranges, yellows, reds and even some multi-coloured variants. You might think this makes it significantly more visible to predators, but to combat this they are able to close off their tubes using a modified radiole/chaetum known as the operculum which acts like a door which can be opened and closed

 

Due to being a sedentary organism, Spirobranchus giganteus  gets its nutrients by filter-feeding. Its upper radioles/chaetae are highly ciliated, meaning that any microorganisms which venture too close to these mouthparts will become trapped and eventually be deposited straight into the Annelid’s digestive tract

 

Talking about the digestive tract, S.giganteus has a very complex digestive system as well as a fully closed circulatory system. Despite being only around 3.8 centimetres in length on average, Spirobranchus has a very well developed internal organ structure, housing a central brain with several supporting ganglia and a nephridium which performs the same function as the kidney in vertebrates, removing waste products from the body

What is your favourite Annelid? It can be in terms of physical or functional beauty...

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