Edrioasteroids, relatives of starfish, used to live on Earth during the Paleozoic (until about 300 million years ago). They looked like starfish, with five arms radiating from a round body. Unlike starfish, which move around, edrioasteroids stayed in one place, using a thick stalk to attach to the sea bottom or other surface. The stalk was covered with small, hard plates that made it more rigid. The body was also plated, providing protection and structure. Even the anus, where wastes were expelled on the underside of the animal, was plated. On the top of an edrioasteroid were five feeding grooves. Each groove channeled water into the body where nutrients could be filtered out. The feeding tubes tended to curve in the same direction, creating a pattern of spirals. Edriosteroids were most diverse in the Ordovician. Like many other organisms, they went extinct in the mass extinction event at the end of the Permian.