Echinoderm are marine animals characterised by a radial symmetry and include well-known animals as starfish, sea urchins, sand dollars, and sea cucumbers. They are found at every ocean depth, from the seashore to the abyss. Echinoderms can regenerate missing limbs, arms, spines and even intestines. Some brittle stars and sea stars can reproduce asexually by breaking a ray or arm or by deliberately splitting the body in half. Each half then becomes a whole new animal.