The correct answer is C. Hydra.
A cockroach is an insect that has a circulatory system that includes a heart, blood vessels, and hemolymph. A snail is a mollusk that has a circulatory system that includes a heart, blood vessels, and hemolymph. A kangaroo is a mammal that has a circulatory system that includes a heart, blood vessels, and blood. A hydra is a cnidarian that does not have a circulatory system.
Cnidarians are a phylum of animals that includes jellyfish, corals, and sea anemones. They are characterized by having a radial body plan, stinging tentacles, and a simple digestive system. Cnidarians do not have a circulatory system, which means that they do not have blood or blood vessels. Instead, they exchange gases directly with the environment through their skin.
Respiration is the process by which an organism takes in oxygen and releases carbon dioxide. Cnidarians respire through diffusion, which is the movement of molecules from an area of high concentration to an area of low concentration. Oxygen diffuses into the cnidarian’s body through its skin, and carbon dioxide diffuses out of the cnidarian’s body through its skin.
The process of respiration is essential for all living organisms. It provides the energy that organisms need to function. Without respiration, organisms would not be able to survive.