Final answer:
Barnacles belong to the phylum Crustacea, characterized by features like an exoskeleton and a variety of specialized organs and structures.
Step-by-step explanation:
Among the choices provided, barnacles are the animals that belong to the phylum Crustacea. Crustaceans are a large and diverse group within the arthropod kingdom, which includes organisms like shrimp, lobsters, crabs, and krill. Characteristics of crustaceans include having an exoskeleton with a carapace, a main body cavity with an expanded circulatory system, a digestive system with a gastric mill and digestive glands, and appendages that shed to allow for growth. It's worth noting that barnacles are non-moving crustaceans that often attach themselves to surfaces, including man-made structures.