Flexi Says: Several types of animals can breathe underwater, including cnidarians (e.g., jellies, coral), crustaceans (e.g., crabs, lobsters), echinoderms (e.g., sea stars, sea cucumbers), and fish. Very simple animals such as jellies take in oxygen from the water by simple diffusion. More complex animals such as lobsters and fish use specialized structures called gills to take in oxygen and remove carbon dioxide.
