Tortoises and Turtles: Flat shell or domed shell?

What is the difference between flat-shelled or dome-shelled tortoises and turtles?

The tortoise has a domed shell. The tortoise lives on land. The domed shell is heavy and acts like a shield or armour to protect them from predators.

The turtle has a flat shell. The turtle lives in water. Flat shells are lighter and better for swimming in water.

The terrapin has a flat shell. The terrapin lives partly on land and partly in the water.

On World Turtle Day®, a day that reminds people to protect all species of tortoises and turtles, it is a day to look at their shells.

The upper shells on a turtle’s or tortoise’s back are called carapace.

Flat shells are better for swimming. Light, flat carapaces have spaces in between the shell bones, called fontanelles, which adds buoyancy (floatation) in the water. Turtles and terrapins have flat shells to adapt to swimming in water.

Most turtles like sea water. Terrapins prefer fresh water, such as ponds, rivers, and streams.


tortoise with a domed shell



terrapin with a flat shell


Photographer: Martina Nicolls


American Tortoise Rescue (ATR), a nonprofit organization established in 1990 for the protection of all species of tortoise and turtle, is celebrating its 17th annual World Turtle Day® on 23 May. ATR created the “shellebration” to celebrate and protect turtles and tortoises and their disappearing habitats around the world.

ATR launched World Turtle Day® to increase respect and knowledge for the world’s oldest creatures. Biologists and other experts predict the disappearance of turtles and tortoises within the next 50 years. ATR’s ultimate goal is to stop the illegal trade in turtles and tortoises around the world.

American Tortoise Rescue

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