Animals are multicellular eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, reproduce sexually, and grow from a hollow sphere of cells, the blastula, during embryonic development. 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 in total. Animals range in size from 8.5 millionths of a metre to long and have complex interactions with each other and their environments, forming intricate food webs. The study of animals is called zoology. Animals may be listed or indexed by many criteria, including taxonomy, status as endangered species, their geographical location, and their portrayal and/or naming in human culture. By common name List of animal names (male, female, young, and group) By aspect List of common household pests List of animal sounds List of animals by number of neurons By domestication List of domesticated animals By eating behaviour List of herbivorous animals List of omnivores List of carnivores By endangered status IUCN Red List endangered species (Animalia) United States Fish and Wildlife Service list of endangered species By extinction List of extinct animals List of extinct birds List of extinct mammals List of extinct cetaceans List of extinct butterflies By region Lists of amphibians by region Lists of birds by region Lists of mammals by region Lists of reptiles by region By individual (real or fictional) Real List of individual cats List of oldest cats List of giant squids List of individual elephants List of historical horses List of leading Thoroughbred racehorses List of individual apes List of individual bears List of giant pandas List of individual birds List of individual bovines List of individual cetaceans List of individual dogs List of oldest dogs List of individual monkeys List of individual pigs List of wealthiest animals Fictional List of fictional bears List of fictional birds List of fictional cats List of fictional pachyderms List of fictional pigs By taxonomical classification Phyla The animal Kingdom contains some 35 extant phyla. Basal animals are delineated according to the following cladogram: Animals: Porifera, Diploblasts Diploblasts: Ctenophora, ParaHoxozoa ParaHoxozoa: Placozoa, Cnidaria, Bilateria/Triploblast Bilateria: Xenacoelomorpha, Nephrozoa Nephrozoa: Protostomes, Deuterostomes Phylum Proarticulata † Disputed if this is in or out of Bilateria and Phylum Xenacoelomorpha is basal Deuterostomia Phylum Chordata Ambulacraria (unranked) Phylum Hemichordata Phylum Echinodermata Phylum Cambroernida † Protostomia Ecdysozoa Phylum