Medium:

The spines of the amazing banded sea urchin (Echinothrix Calamaris)

Sea urchins are spiny, globular animals living on the sea bed,
Inhabiting all oceans and depth zones. Their are 950 species of them. Their tests (hard shells) are round and spiny, they move slowly, crawling with their tube feet or pushing themselves with their spines. Sea urchins feed mostly on Algae but will also eat small slow moving animals. Their predators include sea otters,star fish, eels, and trigger fish,