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One of five kingdoms of organisms: Animalia, Plantae, Fungi, Protista, and Monera. Animals are eukaryotic multicellular organisms that take food into their bodies and that develop from blastula embryos. Animal species are organized into phyla that are defined according to comparative patterns of development, body structures, behavior, biochemical pathways, modes of nutrition, and ancestry. See Animal systematics
Traditionally, animals have been grouped into invertebrates (without backbones) and vertebrates (with backbones). Vertebrates include mammals, amphibians, reptiles, birds, and fish. Members of all other animal phyla, more than 98% of all animal species, are invertebrates. Although invertebrates lack backbones, they achieve physical support by structures ranging from delicate glass spicules, to tough rings and rods, to hydrostatic pressure. The phylum Arthropoda alone comprises more than 1 million known species. If tropical species were better described, the arthropods might include as many as 10 million living species. See Amphibia, Aves, Chondrichthyes, Chordata, Mammalia, Osteichthyes, Reptilia