Worms do not have a hard skeleton to protect themselves and so they tend to live entirely inside the soil or the mud on a river or pond bed.

The word worm is commonly used to describe the earthworm, but there are other kinds of worms, too. The two main kinds of worms are the segmented worms and the round worms. The segmented worms have their bodies divided in small units called segments.

The earthworm is an example of the segmented worm. You can easily see the segments. They are like fleshy rings joined together. The earthworm uses its segments to help it move. Almost all segments have got bristles which the earthworm can stick out or draw in.

An earthworm moves forwards in its burrow by sticking out its bristles on some segments so that they grip the walls of its burrow. The earthworm then squeezes other segments so that they become long and thin and can move forward. Next it makes these segments stick out their bristles to grip the burrow while the other segments now become long and thin and move forward to catch up.

Segmented worms that live on the sea shore are the ragworm and the lug worm. Some small segmented worms live in ponds, lakes and slow moving rivers. Most roundworms are much smaller than segmented worms and many are microscopic. You may see some very small roundworms in pond water. They swim by thrashing about. One moment they throw their body into a curve, the next they straighten it out, and then they throw it into another curve.