Pincushion Sea Urchin

"a hard test or shell composed of fused plates of calcium carbonate covered by a thin dermis and epidermis. The test is rigid, and divides into five ambulacral grooves separated by five interambulacral areas. Each of these areas consists of two rows of plates, so the test includes 20 rows in total. The plates are covered in rounded tubercles, to which the spines are attached. " ~wiki