How many animals and plants do oceanographers think there are left to discover in the worlds oceans?
Life on Earth almost certainly originated in the sea and was more or less restricted to the oceans for the first 3 billion years of evolution. As a result, there is a much greater variety of animal forms in the marine environment than on the land. The seas contain representatives of 28 phyla–the major groupings of animals, such as sponges, crustaceans, molluscs and so on–whereas terrestrial environments have only 11 phyla. The situation is very different, however, at the species level. There are only about 4000 marine-plant species compared with an estimated 250,000 species of terrestrial green plants. Similarly, of the 1.7 million-or-so known animal species, only about one-tenth are from the oceans, with most of these living on or close to the bottom in relatively shallow water. (source:
