CREATURE FEATURE - SEGMENTED WORMS
There are many different kinds of worms in the sea, but probably the most familiar are the segmented worms. Almost all marine segmented worms are known as polychaetes. The most distinguishing feature of these animals is the presence of flattened extensions to each body section, called parapodia. These are sometimes covered in bristles and also possess gills. Parapodia are often used in locomotion.
Unlike the sponges and cnidarians, segmented worms are bilaterally symmetrical (the body has two identical halves) with a head at the front. The head has a brain, or at least, a collection of nerve cells and sensory organs such as eyes.
Polychaetes have very diverse lifestyles. Some, such as the ragworm, are carnivores with strong jaws for catching small invertebrates, which they actively hunt on the sea floor. Others live in tunnels and feed on organic particles in the sediment - the lugworm, for example, leaves a pile of discarded sand at the entrance to its burrow. Another family of polychaetes build and live in tubes, which may be made from mucus, sand or tiny fragments of shells, and extend many tentacles out into the water to catch floating food particles.