Animalia

Animals are  organisms that form the  Animalia. With few exceptions, animals, , are , can , and grow from a hollow sphere of cells, the , during. Over 1.5 million animal  have been —of which around 1 million are —but it has been estimated there are over 7 million animal species in total. Animals range in length from 8.5 millionths of a metre to 33.6 m. They have with each other and their environments, forming intricate s. The kingdom Animalia includes s, but in colloquial use the term animal often refers only to non-human animals. The study of non-human animals is known as.

Most living animal species are in the, a whose members have a  body plan. The Bilateria include the —in which many groups of s are found, such as s, s, and s—and the, containing both the s as well as the s, the latter containing the s. Life forms interpreted as early animals were present in the of the late. Many modern animal phyla became clearly established in the as  during the, which began around 542 million years ago. 6,331 groups of s common to all living animals have been identified; these may have arisen from a single that lived.