Brittle star
Usually they have 5 arms, which can grow long, up to 60 cm, in the largest species. The central disk of brittle stars can be three to eight inches in diameter. Unlike starfish, they live deeper in the ocean. Ophiuroids are known even from abyssal (>6000 m) depths.  However, brittle stars are also common members of reef communities, where they hide under rocks and even within other living organisms. Generally, brittle stars live below 500m of depth.