So there are 285 species of turtles and, obviously, their behaviors very depending on where they live and their size and their social habits. The most noticeable thing about turtles, of course, is their shell. They, actually, are the only animal that exists like this. The upper shell or the top shell is called the carapace and the lower shell is called the plastron. When turtles are scared or feel threatened, they will often withdraw into the shell, so it is protective for them. Some species are very shy.