Description of Metazoa group.
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  nimal From Wikipedia, the free encyclopedia For other uses, see  Animal (disambiguation).  Animalia redirects here. For other uses, see  Animalia (disambiguation).    Animals Temporal range: Ediacaran   –   Recent   Pre Є   Є   O   S   D   C   P   T   J   K    Pg   N      Scientific classification Domain: Eukaryota     (Unranked) Opisthokonta   (Unranked) Holozoa(Unranked) FilozoaKingdom: Animalia   Linnaeus, 1758   Phyla      Subkingdom Parazoa      Porifera     Placozoa     Subkingdom Eumetazoa      Radiata (unranked)      Ctenophora       Cnidaria     Bilateria (unranked)      Orthonectida      Rhombozoa     Acoelomorpha       Chaetognatha     SuperphylumDeuterostomia      Chordata     Hemichordata     Echinodermata     Xenoturbellida     Vetulicolia  †        Protostomia (unranked)      SuperphylumEcdysozoa        Kinorhyncha       Loricifera     Priapulida        Nematoda      Nematomorpha       Onychophora     Tardigrada       Arthropoda     Superphylum Platyzoa      Platyhelminthes     Gastrotricha     Rotifera     Acanthocephala       Gnathostomulida     Micrognathozoa       Cycliophora     SuperphylumLophotrochozoa      Sipuncula     Hyolitha  †         Nemertea     Phoronida     Bryozoa     Entoprocta       Brachiopoda     Mollusca     Annelida  Synonyms      Metazoa  Haeckel, 1874   Animals  are multicellular , eukaryotic organisms of the kingdom  Animalia  (also called Metazoa ). Their  body plan eventually becomes fixed as they develop, although some undergo a process of  metamorphosis later on in their  lives. Most animals are motile,  meaning they can move spontaneously and independently. All animals must ingest other organisms or their products for  sustenance (seeHeterotroph). Most known animal phyla appeared in the fossil record as marine species during the Cambrian explosion, about 542 million years ago. Animals are divided into various sub- groups, some of which are: vertebrates (birds, mammals, amphibians, reptiles, fish);molluscs (clams, oysters, octo puses, squid, snails); arthropods (millipedes, centipedes, insects, spiders, scorpions, crabs,  lobsters,shrimp); annelids (earthworms, leeches); sponges; and  jellyfish.   Contents [hide]    1 Etymology    2 Characteristics  o  2.1 Structure  o  2.2 Reproduction and development  o  2.3 Food and energy sourcing    3 Origin and fossil record    4 Groups of animals  o  4.1 Ctenophora, Porifera, Placozoa, Cnidaria and Bilateria  o  4.2 Deuterostomes  o  4.3 Ecdysozoa  o  4.4 Platyzoa  o  4.5 Lophotrochozoa    5 Model organisms    6 History of classification    7 See also    8 References    9 Bibliography    10 External links  Etymology The word animal comes from the Latin word animalis , meaning having breath . [1]  In everyday non-scientific usage the word excludes humans  –  that is, animal is often used to refer only to non-human members of the kingdom Animalia; often, only closer relatives of humans such as mammals, or mammals and other  vertebrates, are meant. [2]  The biological definition of the word refers to all members of the kingdom Animalia, encompassing creatures as diverse as sponges,  jellyfish, insects, and humans. [3]   Characteristics  Animals have several characteristics that set them apart from other living things. Animals are eukaryotic and multicellular , [4]  which separates them from bacteria and most protists.  They are heterotrophic, [5]  generally digesting food in an internal chamber, which separates them from plants and algae. [6]  They are also distinguished from plants, algae, and fungi by lacking rigid cell walls. [7]   All animals are motile, [8]  if only at certain life stages. In most animals, embryos pass through a blastula stage, [9]  which is a characteristic exclusive to animals. Structure With a few exceptions, most notably the sponges (Phylum Porifera) and Placozoa, animals have bodies differentiated into separatetissues. These include muscles, which are able to contract and control locomotion, and nerve tissues, which send and process signals. Typically, there is also an internal digestive chamber, with one or two openings. [10]   Animals with this sort of organization are called metazoans, or  eumetazoans when the former is used for animals in general. [11]   All animals have eukaryotic cells, surrounded by a characteristic extracellular matrix composed of  collagen and elasticglycoproteins. [12]  This may be calcified to form structures like shells, bones, and spicules. [13]  During development, it forms a relatively flexible framewor k [14]  upon which cells can move about and be reorganized, making complex structures possible. In contrast, other multicellular organisms, like plants and fungi, have cells held in place by cell walls, and so develop by progressive growth. [10]   Also, unique


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