Turtles, tortoises, and terrapins are reptiles that belong to the order Testudines (also called Chelonii). While tortoises belong to the Testudinae family, turtles are chelonians that dwell in freshwater bodies or sea. Different types of turtles are classified under different families. Being reptiles, turtles and tortoises are ectothermic, which means that they don't have an internal mechanism to regulate their body temperature. They need external sources to stay warm. The characteristic feature of turtles, as well as tortoises is their shell. The shell is composed of 59 to 61 bones that are covered by scutes, which are plates made of keratin. It must be noted that the shell is permanently attached to the spine and the rib cage. The top and bottom of the shell is referred to as carapace and plastron, respectively. The reason why these reptiles have a long lifespan is often attributed to their slow metabolism, and the protection provided by the shell against predators. Some of the species can hide their legs and head within the shell, when threatened. Though the skin of turtles and tortoises might look tough, it is actually sensitive. Nerves that are present within the shell are responsible for their ability to sense pressure and pain. Though turtles and tortoises have survived for millions of years, some of the species are now threatened with extinction due to habitat degradation or destruction. Consistent efforts are being made throughout the world to keep their numbers from declining. For instance, a global conservation program for freshwater turtles and tortoises has been launched by San Diego Zoo Global, the Turtle Survival Alliance, and the Wildlife Conservation Society. In North America, the term 'turtles' is used for referring to all chelonians, which also includes tortoises. The species Gopherus polyphemus, which is commonly referred to as gopher tortoise, is the only tortoise that is native to North America. This species has been designated as the state reptile of Georgia and the state tortoise of Florida. The following tortoise vs. turtle comparison chart sums up the differences between a turtle and a tortoise. It must be noted that some of the species of turtles and tortoises are endangered. In states such as Arizona, California, and Nevada, one can keep legally-obtained captive tortoises as pets. In case of California, the tortoise must be registered under the California Department of Fish and Wildlife Code. Thus, there are certain restrictions or regulations that one must be aware of. There are restrictions in case of turtles as well. Since 1975, it is illegal to sell turtles that are less than 4 inches in length. This is to reduce the risk of transmission of Salmonella bacterium. For the same reason, the Centers for Disease Control and Prevention suggests that turtles must not be kept as pets if there are children below the age of 5 years, elderly, or immunocompromised individuals. If you have decided to keep a pet turtle or tortoise, you should remember that they require a lot of care.