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Do turtles ever leave their shells?

February 2004

 

Contrary to what you see in cartoons and storybooks, turtles can’t actually leave their shells. Neither can tortoises or terrapins, which begs the question: What’s the difference between turtles, terrapins and tortoises?


The main difference between these reptiles has more to do with where they live than how they look. Tortoises live their entire lives on land. Terrapins live in brackish water (a mix of salt and freshwater).

 

Loggerhead sea turtle cruises through a shipwreck.

Sea turtles spend their lives in the ocean, except for a few hours each season when females come ashore to dig nests and lay eggs. In the United States we group them all together and call them turtles.


Turtles, tortoises and terrapins all belong to the order testudines. They are vertebrates, which means they have a backbone or vertebral column. In fact, their backbone and rib cage are actually fused to their shells. So if a turtle tried to walk off without its shell it would be leaving its spine and ribs behind.


A turtle’s shell provides not only a home, but also protection from predators and adverse weather. Most land and freshwater turtles can draw their heads into their shells. However, sea turtles are unable to do so because of the extra muscles near their necks. These muscles help them swim powerfully through the ocean during long migrations or when hunting.


Turtle shells are composed of bone and consist of two main parts. The upper part is called the carapace and the lower part is called the plastron. The scales, or scutes, that cover the carapace, and the arrangement of the scutes, can help identify the species of turtle.


Each section of scutes on the carapace is actually named to help with identification. The scutes down the middle are called central scutes. The ones on either side are called costal scutes, and the small ones around the edge are called marginal scutes.


Each species of turtle has its own pattern and coloration for shell design. Some designs are very beautiful, which has led to serious problems for some turtles. Turtles have long been hunted, not only for their meat but also for their shells. This hunting has led to some species becoming endangered, such as the hawksbill sea turtle. Its shell is highly prized for its beauty and is used to make jewelry, bowls, glasses frames, and many other products.