Turtles are reptiles belonging to the order Testudines, distinguished by their hard shells that protect their bodies. There are over 300 species of turtles, found in a variety of habitats including oceans, rivers, lakes, swamps, and dry land. They are broadly classified into two main groups: sea turtles, which live in oceans, and terrestrial and freshwater turtles.

Sea turtles, such as the green turtle (Chelonia mydas) and the leatherback turtle (Dermochelys coriacea), are known for their long migrations between feeding areas and nesting sites. They have flippers instead of legs, which are adapted for swimming long distances. Terrestrial turtles, like the Galápagos tortoise (Chelonoidis nigra), have sturdy legs adapted for walking on land. All turtles are oviparous, laying their eggs in holes dug in sand or soil, where the eggs are incubated by the ambient heat.