Vetulicolia

مشكلة الحيوانات في الشرق الاوسط

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Animal From Wikipedia, the free encyclopedia For other uses, see Animal (disambiguation). "Animalia" redirects here. For other uses, see Animalia (disambiguation). Animals Temporal range: Cryogenian – Recent 670–0Ma Had'nArcheanProterozoicPha. Animal diversity.png Scientific classification Domain: Eukaryota (unranked) Unikonta (unranked) Opisthokonta (unranked) Holozoa (unranked) Filozoa Kingdom: Animalia Linnaeus, 1758 Phyla Subkingdom Parazoa Porifera Placozoa Subkingdom Eumetazoa Radiata (unranked) Ctenophora Cnidaria Trilobozoa † Bilateria (unranked) Acoelomorpha Tullimonstrum † Proarticulata † Mesozoa (unranked) Orthonectida Rhombozoa Monoblastozoa Nephrozoa (unranked) Chaetognatha Superphylum Deuterostomia Chordata Hemichordata Echinodermata Xenoturbellida Vetulicolia † Protostomia (unranked) Superphylum Ecdysozoa Kinorhyncha Loricifera Priapulida Nematoda Nematomorpha Onychophora Tardigrada Arthropoda Superphylum Platyzoa Platyhelminthes Gastrotricha Rotifera Acanthocephala Gnathostomulida Micrognathozoa Cycliophora Superphylum Lophotrochozoa 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). All animals are motile, meaning they can move spontaneously and independently, at some point in their lives. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their lives. All animals are heterotrophs: they must ingest other organisms or their products for sustenance. 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, octopuses, squid, snails); arthropods (millipedes, centipedes, insects, spiders, scorpions, crabs, lobsters, shrimp); annelids (earthworms, leeches); sponges; 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 separate tissues. 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 elastic glycoproteins.[12] This may be calcified to form structures like shells, bones, and spicules.[13] During development, it forms a relatively flexible framework[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 to animal cells are the following intercellular junctions: tight junctions, gap junctions, and desmosomes.[15] Origin and fossil record Further information: Urmetazoan Dunkleosteus was a 10-metre-long (33 ft) prehistoric fish.[38] Animals are generally considered to have evolved from a flagellated eukaryote.[39] Their closest known living relatives are the choanoflagellates, collared flagellates that have a morphology similar to the choanocytes of certain sponges.[40] Molecular studies place animals in a supergroup called the opisthokonts, which also include the choanoflagellates, fungi and a few small parasitic protists.[41] The name comes from the posterior location of the flagellum in motile cells, such as