The burrowing urchin, a.k.a Martha's Sea Urchin, has a nervous system that is different than most sea urchins. The nerve system of the burrowing urchin consists of a central nerve ring, with radial nerves running off along the underside of the test. The main sensory cells of these are located in the epithelium on the tube feet and spines, and also on the buccal organ. These urchins are also believed to be sensitive to light, however the method of which they sense light is unknown.