Each of these ambulacra was roofed by cover plates. Attached to this are five bands of muscle running internally longitudinally along the ambulacra. The food gathering system of blastoids consisted of several types of ambulacra. The area on the shell between ambulacra is known as an interambulacrum. The ambulacra grew either curved or straight. It is pluralized as "ambulacra". Radiating like flower petals from the center were five food grooves, or "ambulacra". As in other Echinozoans, there are five ambulacra separated by five ambulacral grooves, the interambulacra.