4.2

Key groups of marine organisms: The number of phyla living in the oceans is considerably greater than on land. The adults and larvae of many different types of organism are planktonic, drifting in ocean currents. Crustaceans, echinoderms, bony fish and cartilaginous fish are some of the more obvious animals in the oceans, while macroalgae (seaweeds) and seagrasses form the basis of many food chains.