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.
Most animals inhabit the seas, with fewer in fresh water and even fewer on land.
Research continues on the evolutionary relationships of the major groups of animals. Chordata Written by Philip Myers, December 1994. Last updated 14 March 2000. Sponsored in part by the Interagency Education Research Initiative, the Homeland Foundation and the University of Michigan Museum of Zoology . The ADW Team gratefully acknowledges their support.