This green sea urchin (Strongylocentrotus droebachiensis) shell or test close-up shows an interesting pattern across the surface. The test is made up of calcium carbonate to give it strength. The sections with holes are where the green sea urchin would extend its tube feet. The many bumps on the test are where the spines were once attached. A cup-like base to each spine would rest over these bumps. A living green sea urchin can use muscles and tissue attached to the spines to direct them towards a threat. This animal was a herbivore and ate a wide variety of algae. The green sea urchin can grow to 3.6 inches (9 cm) across, with a range that is circumpolar and includes Japan, as well as northern Alaska to northern Washington.