 The tortoises have a large bony carapace ( shell ) of a dull brown colour . The plates of the shell are fused with the ribs in a rigid protective structure that is integral to the skeleton . Lichens can grow on the shells of these slow @-@ moving animals . Tortoises keep a characteristic scute ( shell segment ) pattern on their shells throughout life , though the annual growth bands are not useful for determining age because the outer layers are worn off with time . A tortoise can withdraw its head , neck , and fore limbs into its shell for protection . The legs are large and stumpy , with dry , scaly skin and hard scales . The front legs have five claws , the back legs four . 
