Sea turtles are a collective term for marine turtles belonging to the order Testudines, specifically Cheloniidae and Dermochelyidae.

They have a flat upper jaw and a slightly upturned lower jaw with serrated edges.

They possess a pair of scales on the forehead, and their carapace is heart-shaped with embedded and arranged scutes. Their limbs are paddle-like, with the front limbs longer than the hind limbs, each with a claw, especially prominent in the front limbs, which are curved like hooks. The carapace is typically olive or brown with light-colored markings.

Sea turtles are distributed in the South Pacific and Indian Oceans, primarily inhabiting shallow coastal waters, bays, coral reefs, and estuaries. They feed on large algae, cephalopods, crustaceans, and fish. The breeding season occurs from April to October when they lay eggs in sandy nests.

They may lay eggs 2-3 times a year, with each clutch containing 91-157 eggs. The eggs are white and spherical, with a diameter ranging from 35-58 millimeters, and the incubation period lasts 30 to 90 days. Hatchlings emerge and immediately crawl into the sea to begin their aquatic life.

Apart from nesting and sunbathing, sea turtles spend little time on land. Most turtles exhibit a gentle temperament and retract their heads when encountering threats, relying on their hard shells for protection. With this unique instinct, sea turtles have peacefully coexisted on Earth for 200 million years. Female sea turtles only come ashore during the nesting process.

Despite lacking teeth, their jaws are sharply edged, allowing them to tear or crush hard food easily. The esophagus also contains numerous spines to aid in digestion. Leatherback sea turtles, in particular, can rival the weight of a cow but exhibit surprisingly agile movements. They can swim up to 24 kilometers per hour, nearly matching the speed of dolphins.

Green sea turtles often visit specific "cleaning stations" where fish serve as cleaners, removing debris from their shells to maintain health and facilitate smoother movement. In return, the fish get an easy meal.

Sea turtle shells are smooth, allowing them to swim effortlessly in the sea. Sea turtles cannot retract their heads into their shells like other turtles. Their transparent facial scales act like goggles, enabling them to see underwater. Sea turtles can consume jellyfish without being harmed by their venom.

Sea turtles are known as "living fossils," originating from the late Paleozoic era in the late Permian period, surviving alongside dinosaurs and persisting to the present day. Despite their long existence, sea turtles face extinction threats due to human activities. Accidental injuries from fishing gear, destruction of nesting sites and coral reefs, and unsustainable illegal harvesting of meat, eggs, shells, or specimens are significant threats to sea turtles.