All animals are members of the Kingdom Animalia, also called Metazoa. Most ingest food and digest it in an internal cavity.
Animal cells lack the rigid cell walls that characterize plant cells.
In most, tissues are organized into even more specialized organs. Most animals are capable of complex and relatively rapid movement compared to plants and other organisms. Most reproduce sexually, by means of differentiated eggs and sperm. Most animals are diploid, meaning that the cells of adults contain two copies of the genetic material. Animals range in size from no more than a few cells to organisms weighing many tons, such as blue whales and giant squid.