turtle v. terrapin v. tortoise

The order Testudines (superorder Chelonia) consists of reptiles with horny, toothless jaws, and bony or leathery shells into which the head and limbs can sometimes be withdrawn.

• Turtle can refer to all Testudines, or only ocean-dwelling sea turtles. Aquatic turtles rarely leave the ocean. They may have webbed feet or flippers, and their bodies may be streamlined. Sea turtles can be omnivorous.
• The term terrapin can be applied to species living in fresh or brackish water, (such as rivers, ponds, and swamps), or specifically to the diamondback terrapin.
• Tortoises live on land, are mostly herbivorous, and may not have webbed feet. They belong to the family Testudinidae. In contrast with the flat shells of turtles, tortoise shells are domed, which makes it challenging for predators to crush them with their jaws.

There are exceptions to these naming conventions (e.g., box turtle).

Tortoise burger. Image courtesy of Beer Can Hill.

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