Adult male and female sea turtles are equal in size.
The leatherback is the largest of all living sea turtles. Mature leatherbacks reach about 1.2 to 1.9 m (3.9-6.2 ft.) and 200 to 506 kg (441-1,116 lbs.). The largest leatherback recorded weighed 916 kg (2,019 lbs.).
The Kemp's ridley and olive ridley are the smallest species, and reach about 55 to 75 cm (22-30 in.) and 30 to 50 kg (66-110 lbs.).
Green sea turtles reach about 78 to 112 cm (31-44 in.) and 68 to 186 kg (150-410 lbs.). The largest individual collected was 1.5 m (4.9 ft.) and 395 kg (871 lbs.).
Loggerheads reach about 82 to 105 cm (32-41 in.) and 66 to 101 kg (146-223 lbs.).
Hawksbills reach about 53 to 114 cm (21-45 in.) and 27 to 86 kg (60-190 lbs.).
Flatbacks reach about 81 to 97 cm (32-38 in.) and 60 to 84 kg (132-185 lbs.).
Sea turtles are characterized by a large, streamlined shell.
Depending on the species, sea turtles range can be olive-green, yellow, greenish-brown, reddish-brown, or black in color.
The green sea turtle gets its name from the color of its body fat.
Limbs are flippers adapted for swimming. Sea turtles are awkward and vulnerable on land.
Forelimbs are long and paddle-like.
- Long digits are fused throughout the flipper.
- Only one or two claws are present on each fore flipper.
- A sea turtle swims with powerful wing-like beats of its fore flippers.
Hind flippers serve as rudders, stabilizing and directing the animal as it swims. The hind flippers of some species are quite dexterous at digging nests in the sand.
A sea turtle cannot retract its limbs under its shell as a land turtle can.
A sea turtle cannot retract its head under its shell as a land turtle can.
Sea turtles have large upper eyelids that protect their eyes.
Sea turtles do not have an external ear opening.
Like other turtles, sea turtles lack teeth. Jaw shape varies among species. Each species has a jaw shape adapted for its diet.
The dorsal (top) side of the shell is called the carapace.
- Depending on species, the adult carapace ranges in shape from oval to heart-shaped.
- In all species except the leatherback, the bony shell is composed of broadened, fused ribs, and the backbone is attached to the carapace.
The ventral (bottom) side of the shell is called the plastron.
In all species except the leatherback, the shell is covered with a layer of horny plates called scutes.
- Scutes are firm but flexible, not brittle.
- Scientists can identify sea turtle species by the number and pattern of scutes.
- The leatherback turtle has a thick and oil-suffused skin, which is an excellent insulator, allowing this species to venture into cold water.
- The leatherback's carapace is composed largely of cartilage raised into prominent longitudinal ridges. A layer of thousands of small dermal bones lies just below the leathery skin.
A sea turtle's large, bony shell provides protection from predation and abrasion.
Male and female sea turtles do not differ externally until they approach maturity.
Adult males have longer, thicker tails than females, because the male reproductive organ is housed in the base of the tail. In males, the tail may extend beyond the hind flippers.
With the exception of the leatherback turtle, the claws on the fore flippers of sea turtle males are elongated and curved, which may help them grasp a female's shell during mating.