Insects (Class Insecta) are a major group of arthropos and the most diverse group of animals on the Earth, with over a million described species—more than half of all known living organisms—with estimates of undescribed species as high as 30 million, thus potentially representing over 90% of the differing life forms on the planet. Insects may be found in nearly all environments on the planet, although only a small number of species occur in the oceans, a habitat dominated by the other arthropod group of crustaceans.