Unlike plants and algae, which produce their own nutrients, animals are heterotrophic, feeding on organic material and digesting it internally. Animals are eukaryotic and multicellular. Nonhuman animals have appeared in art from the earliest times and are featured in mythology and religion.Īnimals are unique in having the ball of cells of the early embryo (1) develop into a hollow ball or blastula (2).Īnimals have several characteristics that set them apart from other living things. Dogs have been used in hunting, as have birds of prey, while many terrestrial and aquatic animals were hunted for sports. Humans make use of many animal species, such as for food (including meat, milk, and eggs), for materials (such as leather and wool), as pets, and as working animals including for transport. In modern times, the biological classification of animals relies on advanced techniques, such as molecular phylogenetics, which are effective at demonstrating the evolutionary relationships between taxa. In 1874, Ernst Haeckel divided the animal kingdom into the multicellular Metazoa (now synonymous for Animalia) and the Protozoa, single-celled organisms no longer considered animals. Carl Linnaeus created the first hierarchical biological classification for animals in 1758 with his Systema Naturae, which Jean-Baptiste Lamarck expanded into 14 phyla by 1809. Historically, Aristotle divided animals into those with blood and those without. 6,331 groups of genes common to all living animals have been identified these may have arisen from a single common ancestor that lived 650 million years ago. Many modern animal phyla became clearly established in the fossil record as marine species during the Cambrian explosion, which began around 542 million years ago. Life forms interpreted as early animals were present in the Ediacaran biota of the late Precambrian. The Bilateria include the protostomes, containing invertebrates such as nematodes, arthropods, and molluscs, and the deuterostomes, containing the echinoderms and the chordates, the latter including the vertebrates. Most living animal species are in Bilateria, a clade whose members have a bilaterally symmetric body plan. The scientific study of animals is known as zoology. They have complex interactions with each other and their environments, forming intricate food webs. Animals range in length from 8.5 micrometres (0.00033 in) to 33.6 metres (110 ft). Over 1.5 million living animal species have been described-of which around 1 million are insects-but it has been estimated there are over 7 million animal species in total. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage in which their body consists of a hollow sphere of cells, the blastula, during embryonic development. Animals (also called Metazoa) are multicellular, eukaryotic organisms in the biological kingdom Animalia.
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