Chelonian refers to a group of reptiles that includes turtles, tortoises, and terrapins. These animals are characterized by their bony or cartilaginous shell, which provides protection from predators. Chelonians are found in various habitats, including oceans, rivers, and land, and they play important roles in their ecosystems. The term "chelonians" comes from the Greek word "chelonia," meaning "tortoise." Chelonians are known for their slow movement and long lifespan. They are ectothermic, meaning their body temperature is regulated by their environment. Some well-known species include the green sea turtle and the Galápagos tortoise.