海龜 Sea turtles
Sea turtles (superfamily Chelonioidea), sometimes called marine turtles, are reptiles of the order Testudines and of the suborder Cryptodira. The seven existing species of sea turtles are the green sea turtle, loggerhead sea turtle, Kemp's ridley sea turtle, olive ridley sea turtle, hawksbill sea turtle, flatback sea turtle, and leatherback sea turtle.
For each of the seven types of sea turtles, females and males are the same size; there is no sexual dimorphism. In general, sea turtles have a more fusiform body plan than their terrestrial or freshwater counterparts. This tapering at both ends reduces volume and means that sea turtles can't, as can other turtles and tortoises, retract their head and limbs into their shells for protection. But the streamlined body plan reduces friction and drag in the water and allows sea turtles to swim more easily and swiftly.
The leatherback sea turtle is the largest sea turtle, measuring 2–3 m (6–9 ft) in length, 1–1.5 m (3–5 ft) in width, and weighing up to 700 kg (1500 lb). Other sea turtle species are smaller, being mostly 60–120 cm (2–4 ft) long and proportionally narrower.
The skulls of sea turtles have cheek regions that are enclosed in bone. Although this condition superficially resembles that found in the earliest known fossil reptiles it is very likely a more recently evolved trait in sea turtles.
Do sea turtles like to gather or keep social distance?
Sea turtles are generally solitary creatures that remain submerged for much of the time they are at sea, which makes them extremely difficult to study. They rarely interact with one another outside of courtship and mating. Ridleys, however, do come together in massive groups during nesting.