Adult male and female sea turtles are equal in size.
- Olive ridleys are the smallest sea turtles. They have carapace lengths of about 51 to 75 cm (20 to 30 in.) and weigh
33 to 50 kg (73 to 110 lbs.).
- The Kemp’s ridley has carapace lengths of 52 to 72 cm (20.5 to 28 in.) and weigh 32 to 50 kg (66 to 110 lbs.).
- Green sea turtle carapaces reach about 78 to 120 cm (31 to 47 in.) long; they weigh 68 to 230 kg (150 to 507 lbs.).
- The largest individual collected was 1.5 m (5 ft.) long and weighed 395 kg (871 lbs.).
- The black sea turtle subspecies tends to be smaller with carapace lengths of 59 to 117 cm (23 to 46 in.); they weigh 70 to 120 kg (150 to 265 lbs.).
- Loggerhead carapace lengths reach about 90 to 105 cm (35 to 41 in.) and they weigh 100 to 180 kg (220 to 397 lbs.).
- Adult hawksbills have a carapace length of 53 to 114 cm (21 to 45 in.) and weigh about 43 to 91 kg (95 to 201 lbs.).
- Flatbacks reach carapace lengths of about 81 to 100 cm (32 to 39 in.) and weigh about 60 to 90 kg (132 to 185 lbs.).
- Mature leatherbacks reach carapace lengths of about 1.2 to 1.8 m (47 to 70 in.) and weigh 200 to 900 kg (441 to 1,984 lbs.).
- The leatherback is the largest of all living sea turtles.
- The largest leatherback recorded weighed 916 kg (2,020 lbs.).
Sea turtles are characterized by a large, streamlined shell and non-retractile head and limbs.
Depending on the species, sea turtles' color range can be olive-green, yellow, greenish-brown, reddish-brown, or black in color. Some green turtles and hawksbills have shells patterned with streaks and blotches of brown or black. Leatherbacks have black carapaces (top shells) dotted with white and white plastrons (bottom shells) with dark splotches.
As its common name implies, the black subspecies (Chelonia m. agassizii) of green sea turtle is typically darker than C. m. mydas.
The green sea turtle gets its name from the color of its body fat (due to its diet of seagrasses and algae), not its shell.
Like many other aquatic animals, sea turtles are countershaded with a dark dorsal (back) and light ventral (lower surface) coloration. Countershading camouflages the turtles from potential predators. When viewed from above, the turtle’s dark back blends in with the ocean depths. From below, the lighter ventral side blends in with the brighter sea surface.
Limbs are flippers adapted for swimming. Sea turtles are awkward and vulnerable on land.
Unlike land turtles, a sea turtle cannot retract its limbs under its shell.
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 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.
A sea turtle’s large, bony shell provides protection from predation and abrasion. 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.
- Green sea turtles have 5 central scutes and 4 lateral scutes. The carapace is oval when viewed from above. Adults of the black subspecies have a higher domed carapace.
- Hawksbill turtles have 5 central scutes and 4 lateral scutes. The scutes overlap and are pointed at the back end. The carapace is elliptical when viewed from above.
- Loggerhead turtles have 5 central scutes and 5 lateral scutes.
- Kemp’s ridley turtles have 5 central scutes and 5 lateral scutes. When viewed from above, their carapace is almost completely round.
- Olive ridleys have 5 central scutes and 6 or more lateral scutes. When viewed from above, their carapace is almost completely round.
- Flatback turtles have 5 central scutes and 4 lateral scutes. The carapace is rounded when viewed from above and has a flattened profile. The carapace edges of most adult flatbacks are turned up.
The leatherback turtle has a thick and rubbery oil-suffused skin, which is an excellent insulator, allowing this species to venture into much colder water than other sea turtles. The leatherback’s tear-drop shaped carapace is composed largely of cartilage raised into seven prominent longitudinal ridges. A layer of thousands of small dermal bones lies just below the leathery skin.
The shells of adult green and loggerhead turtles are often covered with algae, barnacles, sponges, skeleton shrimp and other ocean animals. Cleaner fish often follow the turtles closely; dining on the shells’ external occupants and helping to keep the turtle shells clean. This cleaning service benefits the turtle by reducing the amount of drag as the turtle swims.
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.