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56 57 aPPendix iv animaLs Animals range from simple unicellular organisms to highly complex multicellular organisms. They are motile, i.e., able to move spontaneously and independently at least at some point in their lives and they, like plants, consist of single cells or collections of cells that communicate and cooperate with one another. Most animal phyla appeared in the seas of the Cambrian era, around 550 million years ago. The classical taxonomic division of the kingdom animalia is into vertebrates and invertebrates with or without spines. The invertebrate group comprises about 97 of all animal species and includes amoebas, hydras, sponges, worms, mollusks slugs, snails, cnidarians jellyfish, anemones, corals, echinoderms urchins, starfish, cephalopods squid, octopus, cuttlefish and arthropods crustaceans, arachnids, insects. The vertebrate group includes fish, amphibians, reptiles, birds, marsupial mammals and placental mammals. Each extant species is at the apex of its own evolutionary story. The modern classification of the Animal kingdom involves 13 phyla, including at least three containing different kinds of worms. The largest phylum by far is arthropoda, mostly populated by insects, with well over a million named species, and 20 million unnamed. In all, there are probably around 30 million species of plants and animals on Earth, of whom human activity is killing off about 50,000 a year, or 1 every 6 years, the fastest rate of genomicide since the KT extinction which wiped out the dinosaurs along with 85 of all species on Earth. Last time it took 30 million years for the Earth to recover.
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