Testudine reptiles encased in a body shell, and plastron. This includes turtles and tortoises. It contains 14 families of turtles. Some easy and main ways to tell tortoises from other turtles ( all tortoises are turtles but not all turtles are tortoises ) is that tortoises tend to live on land, and have more domed shells. Tortoises also tend to live longer ( The longest living turtle is the galapogos tortoise )They tend to be larger.(Even though the largest turtle is the loggerhead turtle) This is as opposed to turtles who have more flat aerodynamic shell to live underwater. Turtles also tend to be smaller.