Classification of living organisms: plants and animals

Animals are multicellular organisms adapted to life in water, on land and in air, and in soil. They are heterotrophs: they eat ready-made organic matter – herbivores eat plants, predators eat other animals, and some feed on remains or live as parasites. Unlike plants and fungi, most animals move actively (a few, such as polyps and sea squirts, are fixed in place). Their bodies can be radially symmetrical (hydra, starfish) or bilaterally symmetrical (worm, insect, fish, human). The animal kingdom is divided into invertebrates and vertebrates; vertebrates have an internal skeleton for support. The main phyla are coelenterates, worms, molluscs, arthropods and chordates. Chordates are divided into the classes fish, amphibians, reptiles, birds and mammals. The smaller the systematic unit, the more alike its animals are. The main ranks for animals: species, genus (urug‘), family, order (turkum), class, phylum (tip), kingdom.