Spines are made of calcite and are used by regular echinoids for defence and locomotion. Each spine articulates to a tubercle on the test. In the cidarid pictured below there are large primary spines ...

Spines are generally coloured, with pigment incorporated into the calcite of the skeleton. In cross-section (SEM micrographs below) spines may be hollow or solid. The hollow core to a spine is called ...