The Great Barrier Reef Library

A comprehensive guide to The Great Barrier Reef

Annelida – Segmented Worms


By on December 28, 2017


Annelida are extremely common and varied. They range from the earthworms on land, to the Christmas Tree Worms found on the reef. Annelids inhabit most environments on Earth, feeding on a wide range of material and many are even hermaphrodites. To distinguish them from other marine worms, you should be able to notice a distinct, segmented body. Each segment or Metamere, is almost identical, both inside and out, with exception to the head and tail segments – and some other segments in certain Annelids. Inside the segments, the muscles, nerves, blood vessels and even excretory organs are identical.1,2

Whilst they may appear simple, Segmented Worms are actually quite complex, made of a fluid-filled tube, with muscular walls. They have many organs in common with ourselves.  They have a mouth (prostomium) at the front end, which is linked to a digestive tract running the length of its body. This tract terminates at the anus.  The fluid-filled cavity is essentially its skeleton, allowing the muscles to function. Segmented Worms have sensory organs and a brain that is connected to a nervous system. They also have a closed circulatory system.  Annelids exhibit bilateral symmetry and their body has more than two cell layers.2

Since most Fish, Crustaceans and even some people prey upon Annelids, they are generally good at concealing themselves. You often find them hiding under rubble, buried in the sand,or hiding in tubes.2

You can find a list of all of the groups of Annelida found on The Great Barrier Reef, below.


Class – Next level of classification, grouping animals with similar characteristics