Turtles are not animals living inside separate shells. Their shells are permanent parts of their skeletons. The upper shell, called the carapace, and the lower shell, called the plastron, are made of bone covered by keratin. A turtle's ribs and spine are fused to the shell, which protects vital organs and provides structural support. Because the shell contains nerves and blood vessels, turtles can feel sensations through it and cannot leave or outgrow it. Works Cited: Pough, F. Harvey, et al. Herpetology. 4th ed., Sinauer Associates, 2016. Want more interesting content like this ? Follow gravitonomy :) Via : Unknown No copyright infringement intended. Kindly DM for Credit/Removal/Collaboration :) #science #turtles #skeleton #biology