- They have 5 fold symmetry
- Contain 5 ambulacra and 5 interambulacra
- The ambulacra are narrow, consist of 2 rows of plates and contain pore pairs which have tube feet
- Interambulacra- wider, two rows of plates with tubercles
- Tube feet have three main points - movement, respiration and attachment
- The mouth is surronded my a membrane called the peristome
- Edges of the test turned inwards, to produce a lip called the perignathic girdle
- There are 5 jaws each with a sharp tooth supported inside the mouth, called Arisotles lantern
the tubercles consist of two parts the boss a, a wide base and the mamalon , a nipple like structure in the centre of a boss. muscle attaches the spine to the boss, and as a muscle , it can contract and cause the spine to move in a coordinated manner. this means the echinoid can move it spine for walking.
Mode Of Life
regular echinoids live on rocky shores, a high energy enviroment, which is reflected by their robust test and spines.