CHARACTERISTICS: animals with a backbone; periodically shed their whole skin; skin has scales; specially jointed skulls and jaws allow them to open their mouths very wide to swallow unusually large prey KNOWN SPECIES: approximately 6,300 SIZE RANGE: .6 inches to more than 29 feet (1.5 centimeters to more than 9 meters) WHERE THEY LIVE: on land; some in oceans and fresh waters