Which sea turtle species has the largest body and lacks a hard bony shell?

The leatherback sea turtle is the largest sea turtle and lacks a hard bony shell.

Instead of the rigid shell typical of other living sea turtles, the leatherback has a flexible, leathery carapace supported by small bones beneath the skin. Seven prominent ridges run along its back, helping streamline the body during long-distance swimming. Adults can exceed 2 metres in total length and weigh hundreds of kilograms.

Leatherbacks are specialized for feeding on jellyfish and other soft-bodied animals. Their flexible anatomy and thick layer of body fat help them enter colder waters than most other sea turtles. They have been recorded across all major oceans and undertake major migrations between feeding and nesting areas.

The shell is still important for protection, but it is not a detachable covering. Like other sea turtles, leatherbacks breathe air and must surface. They are vulnerable to fisheries bycatch, plastic ingestion and loss of nesting beaches.