Earthworms do not have a backbone. They fall under the category of invertebrates. They do not have bones, legs, eyes, or teeth. A cockroach has six legs, three body segments, and no bones. It has an exoskeleton in place of a skeleton. The endoskeleton is hard and shell-like and covers its body. Snails have no bones, or rings or joints in their bodies. Hence, the correct answer is D.