The chordates have an endoskeleton with a backbone, which allows them to be called vertebrates.
Sturgeons
The Sturgeons are to be consider the bony fishes in the Chordata phylum. This animal has a very tough, yet flexible skeletal structure that has a tough, elastic-like, fibrous tissue which is called cartilage.The tissue is connected to many part of the body such as their sides, lower side, back and most of their head. Its thick cartilage plate serve as a protective armor as it covers the skin. This type fish lack bones. It is believed that this fish inherited the characteristics of the fish in the Devonian Period which is the shark-like tail fin, having the upper lobe larger than the lower lobe.
Sharks
Sharks are also consist cartilage like the sturgeons, but less durable than them. Since the cartilage is less dense than the regular bone, the shark is lighter in water and save energy when swimming in the water for a long time. But since it is less durable, on land the shark may crush their heart, lungs, etc. with their own weight.
Turtles
The turtle is a vertebrate in the chordate category. The turtle's system is just as complex as the human skeleton, only they have less bones. Also their spine is actually fused with the shell on their back. Since they have heavy shells and small arms, they move quite slow. The shell have two different parts; the lower part that protects the belly of the turtle is called the plastron and the upper part is the carapace.