A marine invertebrate (class Asteroidea) that typically has a central disc from which radiate five arms, sometimes more. The upper surface is covered with overlapping plates and is spiny in some species; the mouth is on the lower surface. A hydraulic system operates tube feet used in locomotion and feeding. Many starfish are brightly coloured. They are opportunistic predators on other invertebrates. There are about 1500 species found in all oceans.