Some 2,000 species of marine stars inhabit all the oceans of the world, from tropical habitats to the seabed. Those with five arms are the most common, but there are species with 10, 20, and even 40 arms.
Because the starfish do not have fins, they have "ambulacrale feet" that are found on the bottom of the starfish. The ambulatory feet emerge through openings in the endoskeleton and are expressed externally by open grooves that are found along the oral surface of each arm.
In some circumstances, the feet seem to function as levers, but when moving on vertical surfaces, they form a traction system. The feet adhere to the surface and move in a wave. However, most starfish can not move very fast.