regular echinoids

Main Points

• 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 water vascular system - hydraulic system used for animal to extend its tube feet by forcing water itnto its tissues. this is controlled by the mandreporite

The mouth 

• 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 

Spine Attachment

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.