Reptiles are cold-blooded animals with over 6,800 species worldwide, most having bodies covered with dry, horny scales. They employ various defense mechanisms like hissing, striking, shedding tails, warning colors, camouflage, or tough skin. Major reptile groups include crocodilians, lizards, snakes, and turtles, such as the loggerhead turtle which can lay up to 500 eggs per year.