Turtles (lat. Testudines) are one of the four modern orders of reptiles. A characteristic feature of the structure of turtles is a bone-horn or bone-leather carapace, consisting of two parts: a carapace and a plastron, and serving as the main defense against enemiesGo to the #Shell section. Many species are able to retract their head, tail and limbs under the shell. Length from 12 cm to 2 m. Vision and sense of smell are well developed, hearing is weaker. The jaws are devoid of teeth and covered with horny plates in the form of a beak. The cervical and caudal sections of the spine are mobile, the rest are fixedly fused with the carapace. The appearance of the shell evolutionarily caused the movement of the limb belts under the ribs (an exceptional case among vertebrates).

Terrestrial species of turtles are common on the territory of all continents except Antarctica and on many islands. Marine species are widespread in tropical and subtropical zones, less often in the boreal regions of the oceans. They can live in lakes, rivers, swamps, hot deserts, tropical forests, mountain slopes, cultivated lands, sea coasts, and oceans. Most species lead a semi-aquatic lifestyle. In cold and dry seasons, they can hibernate. Land and sea - mainly herbivorous; freshwater species - usually carnivorous: they can eat fish, amphibians, invertebrates. They usually mate on land, where they lay eggs (from one to several hundred pieces). Some species may have up to 3 or more clutches per year. Eggs are spherical or elliptical, covered in most land species with a calcareous shell, and in marine and some freshwater species with a leathery shell. The incubation period is usually 2-3 months (in the elephant tortoise 6-7 months). Maturity occurs at the age of 2-3 years. Growth is unlimited, but in mature individuals it slows down. Life expectancy up to several decades, sometimes up to 150 years.