17 Surprisingly Cute Photos of Turtles

See snakelike necks, alligatorish backs, and a turtle with two heads.

May 23 is World Turtle Day, a date that advocates for the protection and conservation of the world’s hundreds of turtle species. Turtles are threatened by the illegal pet trade, habitat destruction, and global warming. According to the World Wildlife Fund, nearly all sea turtles are endangered.

To celebrate turtles, we’ve collected pictures that show the incredible diversity of these amazing reptiles. All of the images come from the National Geographic Photo Ark, photographer Joel Sartore's project to document the world's captive species. (Find out which Photo Ark animal is most like you.)

Sartore has traveled around the world and photographed more than 9,000 species with the studio lighting and black-and-white backgrounds that give the collection its iconic look. Photo Ark aims to inspire people not just to care about the natural world, but also to help protect these animals for future generations.