Green Turtle.

Chelonia mydas, commonly known as the green turtle is a large sea turtle belonging to the family Cheloniidae. It is the only species in the genus Chelonia. The range of the species extends throughout tropical and subtropical seas around the world, with two distinct populations in the Atlantic and Pacific Oceans. Their common name derives from the green fat underneath their shell.

The green turtle is the quintessential sea turtle, possessing a dorsoventrally-flattened body covered by a large, teardrop-shaped carapace and a pair of large, paddle-like flippers. Despite the turtle's common name, it is lightly-colored all around while its carapace's hues range from olive-brown to black in Eastern Pacific green turtles. The turtle is actually named for the greenish coloration of its fat and flesh. Unlike other members of its family such as the hawksbill and loggerhead turtles, Chelonia mydas is mostly herbivorous. The adults are commonly found in shallow lagoons, feeding mostly on various species of seagrass.

Like other sea turtles, green turtles are known to migrate long distances between their feeding grounds and the beaches they hatched from. Many islands worldwide have been called Turtle Islands primarily for the large amounts of green turtles that nest on their beaches each year. Female turtles dredge themselves onto beaches and lay eggs in nests that they dig during the night. After a period of time, hatchlings emerge from the nests and head for the water. Those that survive grow to maturity and live to a maximum of eighty years.

As a species recognized as endangered by the IUCN and CITES, Chelonia mydas is protected from exploitation in most countries worldwide. It is illegal to collect, harm or kill individual turtles. In addition, many countries have implemented various laws and ordinances to protect individual turtles and turtle nesting areas within their jurisdiction. However, the turtles' populations are still in danger because of several human practices. In some countries, the turtles are still hunted for their flesh and their eggs are collected from nests and eaten as a delicacy. Pollution indirectly harms the turtle populations both on the population and the individual scale. Many turtles die as a result of being caught in fishermen's nets and drowning. Finally, habitat loss due to human development is a major reason for the loss of green turtle nesting beaches.
Immature Hawaiian C. mydas.

The appearance of the green turtle is that of a typical sea turtle. Chelonia mydas has a dorsoventrally-flattened body, a beaked head at the end of a short neck, and paddle-like arms well-adapted for swimming. Adult green turtles are known to grow to 5 feet (1.5 m) long[5]. While individuals have been caught that reached weights of up to 315 kilograms (695 lb), the average weight of mature individuals is around 200 kilograms (440 lb). The largest Chelonia mydas ever recorded weighed 395 kilograms (871 pounds).

Anatomically, there are a few characteristics that distinguish the green turtle from the other members of its family. Unlike the closely-related hawksbill turtle, the green turtle's snout is very short and its beak is unhooked. The horny sheath of the turtle's upper jaw possesses a slightly-denticulated edge while its lower jaw has stronger, serrated, more defined denticulation. The dorsal surface of the turtle's head has a single pair of prefrontal scales. Its carapace is composed of five central scutes flanked by four pairs of lateral scutes. Underneath, the green turtle has four pairs of infra-marginal scutes covering the area between the turtle's plastron and its shell. Mature C. mydas front appendages have only a single claw (as opposed to the hawksbill's two), although a second claw is sometimes prominent in young specimens.

The carapace of the turtle is known to have various color patterns that change over time. Hatchlings of C. mydas, like those of other marine turtles, have mostly black carapaces and light-colored plastrons. Carapaces of juveniles are dark brown to olive, while those of mature adults are either entirely brown, spotted or marbled with variegated rays. Underneath, the turtle's plastron is hued yellow. C. mydas limbs are dark-colored and lined with yellow, and are usually marked with a large dark brown spot in the center of each appendage.

Sea turtles spend almost all their lives submerged but must breathe air for the oxygen needed to meet the demands of vigorous activity. With a single explosive exhalation and rapid inhalation, sea turtles can quickly replace the air in their lungs. The lungs are adapted to permit a rapid exchange of oxygen and to prevent gasses from being trapped during deep dives. The blood of sea turtles can deliver oxygen efficiently to body tissues even at the pressures encountered during diving. During routine activity green and loggerhead turtles dive for about 4 to 5 minutes and surface to breathe for 1 to 3 seconds. Turtles can rest or sleep underwater for several hours at a time but submergence time is much shorter while diving for food or to escape predators. Breath-holding ability is affected by activity and stress, which is why turtles drown in shrimp trawls and other fishing gear within a relatively short time.