Echinoderms are radially symmetrical animals. This means that the creatures have appendages (or a body construction) which point outward from the centre of the body like the spokes on a bicycle wheel. These appendages usually occur in multiples of five, although there are a few exceptions. Most can regenerate lost limbs.
They are only found in the sea (there are none on land or in fresh water). It contains about 6000 species, and gets its name from the Greek, meaning "spiny skin." Many echinoderms actually do have "spiny" skin, but others do not.
They have bony ossicles in their body. They have a water-vascular system which pumps water through the madroporite. They also have small jaws that are supported by the water-vascular system. And they have tube feet which they use to attach to objects, for protection, as well as to obtain food. They are broken down into 5 different classes, which is looked at in more detail below.