Final answer:
Blood and tissue nematodes are characterized by their heads and tails(A), featuring a radially symmetrical head with sensory bristles and a body covered by a protective cuticle.
Step-by-step explanation:
Blood and tissue nematodes are characterized by their heads and tails(A). These parasitic worms exhibit features such as a radially symmetrical head with sensory bristles and often cuticular formations like teeth around the mouth region. Their bodies are elongated and cylindrical, tapered at both ends and completely covered with a cuticle composed of collagen and chitin which provides a protective layer. Nematodes have a complete digestive system with a mouth opening flanked by three (or six) lips with a muscular pharynx that leads to an intestine and ends with a rectal opening. They move by side-to-side undulations thanks to a layer of longitudinal muscles beneath the epidermis.