Chelonians

Turtles or Chelonians are reptiles of the order Testudinata, which are characterized by having the body protected by a bony shell. While some remained in terrestrial environments (giant tortoises and turtles), others have sought fresh water (tortoises) or ventured out into the sea (sea turtles), evolving and differentiating themselves from the other reptiles.
There were several modifications that allowed the Chelonians to survive for so long and to adapt to new environments. The number of vertebrae was reduced and those that remained fused with the ribs, forming a shell that is sturdy, yet lightweight; in aquatic species, this shell is flatter, resulting in a great hydrodynamic shape.
In the case of marine turtles, their large forelimbs are modified in a form of flipper. They seem to “fly” while swimming, moving with speed and agility. The posterior limbs are paddle-shaped. The head is relatively large and cannot be hidden inside the shell, contrary to other species of turtles.
Being reptiles, their skin is dry and covered with scales, and they regulate their body temperature by the environment temperature. They breath through lungs, but their respiratory and circulatory system is adapted to long periods underwater, either at rest, in search of food, or diving to great depths. Adaptations include slow body function, slower heartbeat and low metabolic rate. They drink saltwater, and have specialized organs and physiology to maintain the balance of salts. Turtles are not animals with a very developed brain, yet they have an extremely well developed sensory system, such as vision, sense of smell and hearing, and have fantastic navigation capabilities. Everything to adapt to life at sea.
They are long-lived species, although there is no scientific proof of the age that they can attain. Sexual maturity is not reached at the same rate among species and individuals. The passage through puberty can occur between 15 and 50 years of age or more, depending on the species and geographical area.
Great migrators and excellent navigators, turtles can swim hundreds of Kilometers during their migrations between feeding and breeding grounds, spending most of their life at sea.