Brittle stars or ophiuroids are echinoderms in the class Ophiuroidea closely related to starfish. They crawl across the seafloor using their flexible arms for locomotion. The ophiuroids generally have five long slender, whip-like arms which may reach up to 60 centimeters (24 in) in length on the largest specimens. They are also known as serpent stars. Ophiuroids have no eyes, or other specialized sense organs. However, they have several types of sensitive nerve ending in their epidermis, and are able to sense chemicals in the water, touch, and even the presence or absence of light.Moreover, tube feet may sense light as well as odors. These are especially found at the ends of their arms, detecting light and retreating into crevices.