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animal
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{{Other uses}}{{redirect |Animalia}}{{pp-semi-indef}}{{pp-move-indef}}{{short description|kingdom of motile multicellular eukaryotic heterotrophic organisms}}{{good article}}{{Use dmy dates |date=October 2012}}{{Use British English |date=April 2017}}{hide}automatic taxobox
| name = Animals
| display_parents = 6
| taxon = Animalia
| authority = Linnaeus, 1758
| fossil_range = Cryogenian – present, {{Long fossil range |665|0{edih}
| image =
File:Animal diversity.png |300pxrect 0 0 118 86 Echinodermrect 0 86 118 172 Cnidariarect 0 172 118 258 Bivalverect 0 258 118 344 Tardigraderect 0 344 118 430 Crustaceanrect 0 430 118 516 Arachnidrect 118 0 236 86 Spongerect 118 86 236 172 Insectrect 118 172 236 258 Mammalrect 118 258 236 344 Bryozoarect 118 344 236 430 Acanthocephalarect 118 430 236 620 Flatwormrect 236 0 354 86 Cephalopodrect 236 86 354 172 Annelidrect 236 172 354 258 Tunicaterect 236 258 354 344 Fishrect 236 344 354 430 Birdrect 236 430 354 620 Phoronida
| image_upright = 1.4
| subdivision_ranks = Superphyla
| subdivision =
{{Collapse top|title=Major animal taxa |left=yes|padding=0|border=0|border2=0|bg=clear|bg2=clear}} Superphylum Deuterostomia Protostomia (unranked)* Superphylum Ecdysozoa* Superphylum Lophotrochozoa{{Collapse bottom}}
| synonyms =
  • Metazoa
}}Animals are multicellular eukaryotic organisms that form the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can 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 animal species in total. Animals range in length from 8.5 millionths of a metre to {{convert|33.6|m|ft}} and have complex interactions with each other and their environments, forming intricate food webs. The category includes humans, but in colloquial use the term animal often refers only to non-human animals. The study of non-human animals is known as zoology.Most living animal species are in the Bilateria, a clade whose members have a bilaterally symmetric body plan. The Bilateria include the protostomes—in which many groups of invertebrates are found, such as nematodes, arthropods, and molluscs—and the deuterostomes, containing the echinoderms and chordates (including the vertebrates). Life forms interpreted as early animals were present in the Ediacaran biota of the late Precambrian. Many modern animal phyla became clearly established in the fossil record as marine species during the Cambrian explosion which began around 542 million years ago. 6,331 groups of genes common to all living animals have been identified; these may have arisen from a single common ancestor that lived 650 million years ago.Aristotle divided animals into those with blood and those without. Carl Linnaeus created the first hierarchical biological classification for animals in 1758 with his Systema Naturae, which Jean-Baptiste Lamarck expanded into 14 phyla by 1809. In 1874, Ernst Haeckel divided the animal kingdom into the multicellular Metazoa (now synonymous with Animalia) and the Protozoa, single-celled organisms no longer considered animals. In modern times, the biological classification of animals relies on advanced techniques, such as molecular phylogenetics, which are effective at demonstrating the evolutionary relationships between animal taxa.Humans make use of many other animal species for food, including meat, milk, and eggs; for materials, such as leather and wool; as pets; and as working animals for power and transport. Dogs have been used in hunting, while many terrestrial and aquatic animals are hunted for sport. Non-human animals have appeared in art from the earliest times and are featured in mythology and religion.

Etymology

The word "animal" comes from the Latin {{wiktlat |animalis}}, meaning having breath, having soul or living being.BOOK, Cresswell, Julia, The Oxford Dictionary of Word Origins, 2010, Oxford University Press, New York, 2nd, 978-0-19-954793-7, 'having the breath of life', from anima 'air, breath, life'., The biological definition includes all members of the kingdom Animalia.ENCYCLOPEDIA, 2006, Animal, The American Heritage Dictionary, Houghton Mifflin Company, 4th, In colloquial usage, as a consequence of anthropocentrism, the term animal is sometimes used nonscientifically to refer only to non-human animals.WEB, English Oxford Living Dictionaries, animal,weblink 26 July 2018, JOURNAL, Boly, Melanie, Seth, Anil K., Wilke, Melanie, Ingmundson, Paul, Baars, Bernard, Laureys, Steven, Edelman, David, Tsuchiya, Naotsugu, 2013, Consciousness in humans and non-human animals: recent advances and future directions, Frontiers in Psychology, 4, 625, 10.3389/fpsyg.2013.00625, 3814086, 24198791, WEB,weblink The use of non-human animals in research, 7 June 2018, WEB,weblink Nonhuman definition and meaning {{!, Collins English Dictionary |publisher=Collins |access-date=7 June 2018}}

Characteristics

File:Blastulation.png|thumb|upright=1.3|Animals are unique in having the ball of cells of the early embryo (1) develop into a hollow ball or blastulablastulaAnimals have several characteristics that set them apart from other living things. Animals are eukaryotic and multicellular,BOOK, Avila, Vernon L., Biology: Investigating Life on Earth,weblink 1995, Jones & Bartlett Learning, 978-0-86720-942-6, 767–, WEB, Palaeos:Metazoa,weblink Palaeos, 25 February 2018, unlike bacteria, which are prokaryotic, and unlike protists, which are eukaryotic but unicellular. Unlike plants and algae, which produce their own nutrientsWEB, Davidson, Michael W., Animal Cell Structure,weblink 20 September 2007,weblink" title="web.archive.org/web/20070920235924weblink">weblink 20 September 2007, no, animals are heterotrophic,WEB, Bergman, Jennifer, Heterotrophs,weblink 30 September 2007,weblink" title="web.archive.org/web/20070829051950weblink">weblink 29 August 2007, no, feeding on organic material and digesting it internally.JOURNAL, Douglas, Angela E., Raven, John A., Genomes at the interface between bacteria and organelles, Philosophical Transactions of the Royal Society B, 358, 1429, 5–17, January 2003, 12594915, 1693093, 10.1098/rstb.2002.1188, With very few exceptions, animals breathe oxygen and respire aerobically.JOURNAL, Mentel, Marek, Martin, William, Anaerobic animals from an ancient, anoxic ecological niche, BMC Biology, 8, 32, 2010, 10.1186/1741-7007-8-32, 20370917, 2859860, All animals are motileWEB,weblink Saupe, S.G., Concepts of Biology, 30 September 2007, (able to spontaneously move their bodies) during at least part of their life cycle, but some animals, such as sponges, corals, mussels, and barnacles, later become sessile. The blastula is a stage in embryonic development that is unique to most animals,BOOK, Minkoff, Eli C., Barron's EZ-101 Study Keys Series: Biology, 2008, Barron's Educational Series, 978-0-7641-3920-8, 2nd, revised, 48, allowing cells to be differentiated into specialised tissues and organs.

Structure

All animals are composed of cells, surrounded by a characteristic extracellular matrix composed of collagen and elastic glycoproteins.BOOK, Alberts, Bruce, Johnson, Alexander, Lewis, Julian, Raff, Martin, Roberts, Keith, Walter, Peter, Molecular Biology of the Cell, 4th, 2002, Garland Science,weblink 978-0-8153-3218-3, During development, the animal extracellular matrix forms a relatively flexible framework upon which cells can move about and be reorganised, making the formation of complex structures possible. This may be calcified, forming structures such as shells, bones, and spicules.BOOK, Sangwal, Keshra, Additives and crystallization processes: from fundamentals to applications, 2007, John Wiley and Sons, 978-0-470-06153-4, 212, In contrast, the cells of other multicellular organisms (primarily algae, plants, and fungi) are held in place by cell walls, and so develop by progressive growth.BOOK, Becker, Wayne M., The world of the cell, 1991, Benjamin/Cummings, 978-0-8053-0870-9, Animal cells uniquely possess the cell junctions called tight junctions, gap junctions, and desmosomes.BOOK, Magloire, Kim, Cracking the AP Biology Exam, 2004–2005 Edition, 2004, The Princeton Review, 978-0-375-76393-9, 45, With few exceptions—in particular, the sponges and placozoans—animal bodies are differentiated into tissues.BOOK,weblink Biology: Concepts and Applications without Physiology, Starr, Cecie, 2007-09-25, Cengage Learning, 978-0-495-38150-1, 362, 365, These include muscles, which enable locomotion, and nerve tissues, which transmit signals and coordinate the body. Typically, there is also an internal digestive chamber with either one opening (in Ctenophora, Cnidaria, and flatworms) or two openings (in most bilaterians).BOOK, Hillmer, Gero, Lehmann, Ulrich, Translated by J. Lettau, Fossil Invertebrates, 1983, CUP Archive, 978-0-521-27028-1, 54,weblink

Reproduction and development

{{see also|Sexual reproduction#Animals|Asexual reproduction#Examples in animals}}File:Odonata copulation.jpg|thumb|Sexual reproduction is nearly universal in animals, such as these dragonflies.]]Nearly all animals make use of some form of sexual reproduction.BOOK, Knobil, Ernst, Encyclopedia of reproduction, Volume 1, 1998, Academic Press, 978-0-12-227020-8, 315, They produce haploid gametes by meiosis; the smaller, motile gametes are spermatozoa and the larger, non-motile gametes are ova.BOOK, Schwartz, Jill, Master the GED 2011, 2010, Peterson's, 978-0-7689-2885-3, 371, These fuse to form zygotes,BOOK, Hamilton, Matthew B., Population genetics, 2009, Wiley-Blackwell, 978-1-4051-3277-0, 55, which develop via mitosis into a hollow sphere, called a blastula. In sponges, blastula larvae swim to a new location, attach to the seabed, and develop into a new sponge.BOOK, Ville, Claude Alvin, Walker, Warren Franklin, Barnes, Robert D., General zoology, 1984, Saunders College Pub, 978-0-03-062451-3, 467, In most other groups, the blastula undergoes more complicated rearrangement.BOOK, Hamilton, William James, Boyd, James Dixon, Mossman, Harland Winfield, Human embryology: (prenatal development of form and function), 1945, Williams & Wilkins, 330, It first invaginates to form a gastrula with a digestive chamber and two separate germ layers, an external ectoderm and an internal endoderm.BOOK, Philips, Joy B., Development of vertebrate anatomy, 1975, Mosby, 978-0-8016-3927-2, 176, In most cases, a third germ layer, the mesoderm, also develops between them.BOOK, The Encyclopedia Americana: a library of universal knowledge, Volume 10, 1918, Encyclopedia Americana Corp., 281, These germ layers then differentiate to form tissues and organs.BOOK, Romoser, William S., Stoffolano, J.G., The science of entomology, 1998, WCB McGraw-Hill, 978-0-697-22848-2, 156, Repeated instances of mating with a close relative during sexual reproduction generally leads to inbreeding depression within a population due to the increased prevalence of harmful recessive traits.JOURNAL, Charlesworth, D., Willis, J.H., The genetics of inbreeding depression, Nat. Rev. Genet., 10, 11, 783–796, 2009, 19834483, 10.1038/nrg2664, BOOK, Bernstein, H., Hopf, F.A., Michod, R.E., The molecular basis of the evolution of sex, Adv. Genet., 24, 323–370, 1987, 3324702, 10.1016/s0065-2660(08)60012-7, Advances in Genetics, 978-0-12-017624-3, Animals have evolved numerous mechanisms for avoiding close inbreeding.JOURNAL, Pusey, Anne, Wolf, Marisa, Inbreeding avoidance in animals, Trends Ecol. Evol., 11, 5, 201–206, 1996, 21237809, 10.1016/0169-5347(96)10028-8, In some species, such as the splendid fairywren (Malurus splendens), females benefit by mating with multiple males, thus producing more offspring of higher genetic quality.JOURNAL, Petrie, M., Kempenaers, B., 1998, Extra-pair paternity in birds: Explaining variation between species and populations, Trends in Ecology and Evolution, 13, 2, 52–57, 10.1016/s0169-5347(97)01232-9, 21238200, Some animals are capable of asexual reproduction, which often results in a genetic clone of the parent. This may take place through fragmentation; budding, such as in Hydra and other cnidarians; or parthenogenesis, where fertile eggs are produced without mating, such as in aphids.BOOK, Adiyodi, K.G., Hughes, Roger N., Adiyodi, Rita G., Reproductive Biology of Invertebrates, Volume 11, Progress in Asexual Reproduction, July 2002, Wiley, 116, 978-0-471-48968-9, WEB, Schatz, Phil, Concepts of Biology {{!, How Animals Reproduce |url=http://philschatz.com/biology-concepts-book/contents/m45547.html |publisher=OpenStax College |accessdate=5 March 2018}}

Ecology

File:Ultramarine Flycatcher (Ficedula superciliaris) Naggar, Himachal Pradesh, 2013 (cropped).JPG|thumb|upright|left|Predators, such as this ultramarine flycatcherultramarine flycatcherAnimals are categorised into ecological groups depending on how they obtain or consume organic material, including carnivores, herbivores, omnivores, detritivores,BOOK, Geomorphology and environmental impact assessment, 2001, Taylor & Francis, 978-90-5809-344-8, Marchetti, Mauro, Rivas, Victoria, 84, and parasites.BOOK, Levy, Charles K., Elements of Biology, 1973, Appleton-Century-Crofts, 978-0-390-55627-1, 108, Interactions between animals form complex food webs. In carnivorous or omnivorous species, predation is a consumer-resource interaction where a predator feeds on another organism (called its prey).BOOK, Begon, M., Townsend, C., Harper, J., 1996, Ecology: Individuals, populations and communities, Third, Blackwell Science, 978-0-86542-845-4, Selective pressures imposed on one another lead to an evolutionary arms race between predator and prey, resulting in various anti-predator adaptations.BOOK, Ecology of marine fishes: California and adjacent waters, 2006, University of California Press, 978-0-520-24653-9, Allen, Larry Glen, Pondella, Daniel J., Horn, Michael H., 428, BOOK, Caro, Tim, Tim Caro, Antipredator Defenses in Birds and Mammals, 2005, University of Chicago Press, 1–6 and passim, Almost all multicellular predators are animals.JOURNAL, 10.1016/j.cub.2004.08.038, 15341755, The real 'kingdoms' of eukaryotes, Current Biology, 14, 17, R693–696, 2004, Simpson, Alastair G.B, Roger, Andrew J, Some consumers use multiple methods; for example, in parasitoid wasps, the larvae feed on the hosts' living tissues, killing them in the process,JOURNAL, Stevens, Alison N.P., Predation, Herbivory, and Parasitism, Nature Education Knowledge, 2010, 3, 10, 36,weblink 12 February 2018, but the adults primarily consume nectar from flowers.JOURNAL, Jervis, M.A., Kidd, N.A.C, November 1986, Host-Feeding Strategies in Hymenopteran Parasitoids, Biological Reviews, 61, 4, 395–434, 10.1111/j.1469-185x.1986.tb00660.x, Other animals may have very specific feeding behaviours, such as hawksbill sea turtles that primarily eat sponges.JOURNAL, Meylan, Anne, Spongivory in Hawksbill Turtles: A Diet of Glass, Science, 239, 4838, 393–395, 1988-01-22, 10.1126/science.239.4838.393, 17836872, 1700236, 1988Sci...239..393M, File:Expl0072 - Flickr - NOAA Photo Library.jpg|thumb|Hydrothermal ventHydrothermal ventMost animals rely on the energy produced by plants through photosynthesis. Herbivores eat plant material directly, while carnivores, and other animals on higher trophic levels, typically acquire energy (in the form of reduced carbon) by eating other animals. The carbohydrates, lipids, proteins, and other biomolecules are broken down to allow the animal to grow and to sustain biological processes such as locomotion.BOOK, Understanding Science: Upper Primary, Clutterbuck, Peter, 2000, Blake Education, 978-1-86509-170-9, 9, BOOK, Gupta, P.K., Genetics Classical To Modern, Rastogi Publications, 978-81-7133-896-2, 26, 1900, BOOK, Garrett, Reginald, Grisham, Charles M., Biochemistry, 2010, Cengage Learning, 978-0-495-10935-8, 535, Animals living close to hydrothermal vents and cold seeps on the dark sea floor do not depend on the energy of sunlight.JOURNAL, none, 1996, New Scientist, 152, 2050–2055, 105, Rather, archaea and bacteria in these locations produce organic matter through chemosynthesis (by oxidizing inorganic compounds, such as methane) and form the base of the local food web.BOOK, Castro, Peter, Huber, Michael E., Marine Biology, McGraw-Hill, 2007, 7th, 376, 978-0-07-722124-9, Animals originally evolved in the sea. Lineages of arthropods colonised land around the same time as land plants, probably between 510–471 million years ago during the Late Cambrian or Early Ordovician.JOURNAL, 10.1016/j.cub.2013.01.026, 23375891, Molecular Timetrees Reveal a Cambrian Colonization of Land and a New Scenario for Ecdysozoan Evolution, Current Biology, 23, 5, 392–8, 2013, Rota-Stabelli, Omar, Daley, Allison C., Pisani, Davide,weblink 1 March 2018, Vertebrates such as the lobe-finned fish Tiktaalik started to move on to land in the late Devonian, about 375 million years ago.JOURNAL, Nature (journal), Nature, 440, 757–763, 6 April 2006, 10.1038/nature04639, A Devonian tetrapod-like fish and the evolution of the tetrapod body plan,weblink Daeschler, Edward B., Shubin, Neil H., Jenkins, Farish A., Jr., 16598249, 7085, 2006Natur.440..757D, JOURNAL, Jennifer A. Clack, Clack, Jennifer A., Scientific American,weblink Getting a Leg Up on Land, 21 November 2005, Animals occupy virtually all of earth's habitats and microhabitats, including salt water, hydrothermal vents, fresh water, hot springs, swamps, forests, pastures, deserts, air, and the interiors of animals, plants, fungi and rocks.BOOK, Margulis, Lynn, Lynn Margulis, Schwartz, Karlene V., Dolan, Michael, Diversity of Life: The Illustrated Guide to the Five Kingdoms,weblink 1999, Jones & Bartlett Learning, 978-0-7637-0862-7, 115–116, Animals are however not particularly heat tolerant; very few of them can survive at constant temperatures above {{convert|50|°C|0|abbr=on}}.JOURNAL, 10.1017/S1473550413000438, The thermal limits to life on Earth, International Journal of Astrobiology, 13, 2, 141–154, 2014, Clarke, Andrew, 2014IJAsB..13..141C,weblink Only very few species of animals (mostly nematodes) inhabit the most extreme cold deserts of continental Antarctica.WEB, Land animals,weblink British Antarctic Survey, 7 March 2018,

Diversity

File:Anim1754 - Flickr - NOAA Photo Library (1).jpg|thumb|The blue whaleblue whale

Largest and smallest

{{further|Largest organisms|Smallest organisms}}The blue whale (Balaenoptera musculus) is the largest animal that has ever lived, weighing up to 190 metric tonnes and measuring up to {{convert|33.6|m|ft}} long.BOOK, Wood, Gerald, The Guinness Book of Animal Facts and Feats, 1983, 978-0-85112-235-9, WEB, Davies, Ella, The longest animal alive may be one you never thought of,weblink BBC Earth, 1 March 2018, 20 April 2016, WEB,weblink Largest mammal, Guinness World Records, The largest extant terrestrial animal is the African bush elephant (Loxodonta africana), weighing up to 12.25 tonnes and measuring up to {{convert|10.67|m|ft}} long. The largest terrestrial animals that ever lived were titanosaur sauropod dinosaurs such as Argentinosaurus, which may have weighed as much as 73 tonnes.JOURNAL, Mazzetta, Gerardo V., Christiansen, Per, Fariña, Richard A., 2004, Giants and Bizarres: Body Size of Some Southern South American Cretaceous Dinosaurs, Historical Biology, 16, 2–4, 71–83, 10.1080/08912960410001715132, 10.1.1.694.1650, Several animals are microscopic; some Myxozoa (obligate parasites within the Cnidaria) never grow larger than 20 Âµm,WEB,weblink Myxozoa, Fiala, Ivan, 10 July 2008, Tree of Life Web Project, 4 March 2018, and one of the smallest species (Myxobolus shekel) is no more than 8.5 Âµm when fully grown.JOURNAL, Two new species of Myxobolus (Myxozoa: Myxosporea: Bivalvulida) infecting an Indian major carp and a cat fish in wetlands of Punjab, India, 3235390, 23024499, 10.1007/s12639-011-0061-4, 35, 2, 2011, Journal of Parasitic Diseases, 169–176, Kaur, H., Singh, R.,

Numbers and habitats

The following table lists estimated numbers of described extant species for the animal groups with the largest numbers of species,JOURNAL, Zhang, Zhi-Qiang, Animal biodiversity: An update of classification and diversity in 2013. In: Zhang, Z.-Q. (Ed.) Animal Biodiversity: An Outline of Higher-level Classification and Survey of Taxonomic Richness (Addenda 2013), Zootaxa, 3703, 1, 2013-08-30, 10.11646/zootaxa.3703.1.3,weblink 5, along with their principal habitats (terrestrial, fresh water,BOOK, Balian, E.V., Lévêque, C., Segers, H., K., Martens, Freshwater Animal Diversity Assessment,weblink 2008, Springer, 978-1-4020-8259-7, 628, and marine),WEB, Hogenboom, Melissa, There are only 35 kinds of animal and most are really weird,weblink BBC earth, and free-living or parasitic ways of life.BOOK, Poulin, Robert, Robert Poulin (zoologist), Evolutionary Ecology of Parasites, Princeton University Press, 2007, 978-0-691-12085-0, 6, Species estimates shown here are based on numbers described scientifically; much larger estimates have been calculated based on various means of prediction, and these can vary wildly. For instance, around 25,000–27,000 species of nematodes have been described, while published estimates of the total number of nematode species include 10,000–20,000; 500,000; 10 million; and 100 million.BOOK, Felder, Darryl L., Camp, David K., Gulf of Mexico Origin, Waters, and Biota: Biodiversity,weblink 2009, Texas A&M University Press, 978-1-60344-269-5, 1111, Using patterns within the taxonomic hierarchy, the total number of animal species—including those not yet described—was calculated to be about 7.77 million in 2011.WEB, How many species on Earth? About 8.7 million, new estimate says,weblink 2 March 2018, 24 August 2011, JOURNAL, Mora, Camilo, Tittensor, Derek P., Adl, Sina, Simpson, Alastair G.B., Worm, Boris, Mace, Georgina M., How Many Species Are There on Earth and in the Ocean?, PLoS Biology, 9, 8, 2011-08-23, 10.1371/journal.pbio.1001127, e1001127, 21886479, 3160336, {{efn|The application of DNA barcoding to taxonomy further complicates this; a 2016 barcoding analysis estimated a total count of nearly 100,000 insect species for Canada alone, and extrapolated that the global insect fauna must be in excess of 10 million species, of which nearly 2 million are in a single fly family known as gall midges (Cecidomyiidae).JOURNAL, Hebert, Paul D.N., Ratnasingham, Sujeevan, Zakharov, Evgeny V., Telfer, Angela C., Levesque-Beaudin, Valerie, Milton, Megan A., Pedersen, Stephanie, Jannetta, Paul, deWaard, Jeremy R., Counting animal species with DNA barcodes: Canadian insects, Philosophical Transactions of the Royal Society B: Biological Sciences, 1 August 2016, 371, 1702, 20150333, 10.1098/rstb.2015.0333, 27481785, 4971185, }}{|class="wikitable"! Phylum! Example! No. ofSpecies! Land! Sea! Freshwater! Free-living! Parasitic
|Annelids
100px)17,000|Yes (soil)|Yes|1,750|Yes|400
|Arthropods
alt=wasp|100px)1,257,000TITLE=HOW MANY SPECIES OF INSECTS AND OTHER TERRESTRIAL ARTHROPODS ARE THERE ON EARTH? VOLUME=63 DATE=JANUARY 2018 PMID=28938083, 31–45, Stork notes that 1m insects have been named, making much larger predicted estimates.40,000(Malac-ostraca)2002 VOLUME=19.2A PUBLISHER=CSIRO PUBLISHING CHAPTER=INTRODUCTION PAGES=1–7,weblink |94,000|Yes45,000{{efn>Not including parasitoids.}}
|Bryozoa
100px)6,000||Yes|60-80|Yes|
|Chordates
alt=green spotted frog facing right|100px)65,00045,000LAST2=WILSON LAST3=WILSON AUTHOR3LINK=E. O. WILSON URL=HTTPS://BOOKS.GOOGLE.COM/BOOKS?ID=-X5OAGAAQBAJ&PG=PA90 PUBLISHER=JOSEPH HENRY PRESS PAGE=90, |13,000|18,0009,000|YesLAST2=BURTON TITLE=ESSENTIAL FISH BIOLOGY: DIVERSITY, STRUCTURE AND FUNCTION YEAR=2017 ISBN=978-0-19-878555-2 QUOTE=TRICHOMYCTERIDAE ... INCLUDES OBLIGATE PARASITIC FISH. THUS 17 GENERA FROM 2 SUBFAMILIES, VANDELLIINAE; 4 GENERA, 9SPP. AND STEGOPHILINAE; 13 GENERA, 31 SPP. ARE PARASITES ON GILLS (VANDELLIINAE) OR SKIN (STEGOPHILINES) OF FISH.,
|Cnidaria
alt=Table coral|100px)16,000||Yes|Yes (few)|Yes|>1,350(Myxozoa)
|Echinoderms
100px)7,500||7,500||Yes|
|Molluscs
alt=snail|100px)85,000107,000JOURNAL=SYSTEMATIC ZOOLOGY ISSUE=2 PAGES=251–254 JSTOR=2412618, |60,000|5,00012,000|Yes|>5,600
|Nematodes
100px)25,000|Yes (soil)|4,000|2,000|11,000|14,000
|Platyhelminthes
100px)29,500TITLE=GLOBAL DIVERSITY OF LAND PLANARIANS (PLATYHELMINTHES, TRICLADIDA, TERRICOLA): A NEW INDICATOR-TAXON IN BIODIVERSITY AND CONSERVATION STUDIESVOLUME=8 PAGES=1663–1681 YEAR=1999, |Yes|1,300|Yes|>40,000
|Rotifers
100px)2,000|400FONTANETO TITLE=MARINE ROTIFERS {{!, An Unexplored World of Richness publisher=JMBA Global Marine Environment pages=4–5}}|2,000|Yes|
|Sponges
100px)10,800||Yes|200-300|YesLAST2=KRASNOV LAST3=LITTLEWOOD TITLE=PARASITE DIVERSITY AND DIVERSIFICATION YEAR=2015 ISBN=978-1-107-03765-6, 44,
! colspan=8 |{{centre|Total number of described species {{as of|2013|lc=y}}: 1,525,728}}

Evolutionary origin

{{Further |Urmetazoan}}File:DickinsoniaCostata.jpg|thumb|left|Dickinsonia costata from the Ediacaran biotaEdiacaran biotaThe first fossils that might represent animals appear in the 665-million-year-old rocks of the Trezona Formation of South Australia. These fossils are interpreted as most probably being early sponges.JOURNAL, Possible animal-body fossils in pre-Marinoan limestones from South Australia, Nature Geoscience, 3, 653–659, 17 August 2010,weblink 10.1038/ngeo934, 9, 2010NatGe...3..653M, Maloof, Adam C., Rose, Catherine V., Beach, Robert, Samuels, Bradley M., Calmet, Claire C., Erwin, Douglas H., Poirier, Gerald R., Yao, Nan, Simons, Frederik J., The oldest animals are found in the Ediacaran biota, towards the end of the Precambrian, around 610 million years ago. It had long been doubtful whether these included animals,JOURNAL, Shen, Bing, Dong, Lin, Xiao, Shuhai, Kowalewski, MichaÅ‚, 2008, The Avalon Explosion: Evolution of Ediacara Morphospace,weblink Science, 319, 5859, 81–84, 10.1126/science.1150279, 18174439, 2008Sci...319...81S, JOURNAL,weblink Late Ediacaran trackways produced by bilaterian animals with paired appendages, Zhe, Chen, Xiang, Chen, Chuanming, Zhou, Xunlai, Yuan, Shuhai, Xiao, 1 June 2018, Science Advances, 4, 6, eaao6691, 10.1126/sciadv.aao6691, 29881773, 5990303, BOOK, Schopf, J. William, Evolution!: facts and fallacies, 1999, Academic Press, 978-0-12-628860-5, 7, but the discovery of the animal lipid cholesterol in fossils of Dickinsonia establishes that these were indeed animals. Animals are thought to have originated under low-oxygen conditions, suggesting that they were capable of living entirely by anaerobic respiration, but as they became specialized for aerobic metabolism they became fully dependent on oxygen in their environments.JOURNAL, Zimorski, Verena, Mentel, Marek, Tielens, Aloysius G.M., Martin, William F., Energy metabolism in anaerobic eukaryotes and Earth's late oxygenation, Free Radical Biology and Medicine, 2019, 10.1016/j.freeradbiomed.2019.03.030, File:Anomalocaris_NT_small.jpg|thumb|Anomalocaris canadensis is one of the many animal species that emerged in the Cambrian explosion, starting some 542 million years ago, and found in the fossil beds of the Burgess shaleBurgess shaleMany animal phyla first appear in the fossil record during the Cambrian explosion, starting about 542 million years ago, in beds such as the Burgess shale. Extant phyla in these rocks include molluscs, brachiopods, onychophorans, tardigrades, arthropods, echinoderms and hemichordates, along with numerous now-extinct forms such as the predatory Anomalocaris. The apparent suddenness of the event may however be an artefact of the fossil record, rather than showing that all these animals appeared simultaneously.JOURNAL, Maloof, A.C., Porter, S.M., Moore, J.L., Dudas, F.O., Bowring, S.A., Higgins, J.A., Fike, D.A., Eddy, M.P., The earliest Cambrian record of animals and ocean geochemical change, Geological Society of America Bulletin, 2010, 122, 11–12, 1731–1774, 10.1130/B30346.1,weblink 2010GSAB..122.1731M, WEB, New Timeline for Appearances of Skeletal Animals in Fossil Record Developed by UCSB Researchers,weblink The Regents of the University of California, 1 September 2014, 10 November 2010, JOURNAL, Conway-Morris, S., Simon Conway Morris, The Cambrian "explosion" of metazoans and molecular biology: would Darwin be satisfied?, The International Journal of Developmental Biology, 2003, 47, 7–8, 505–515, 14756326,weblink WEB, The Tree of Life,weblink The Burgess Shale, Royal Ontario Museum, 28 February 2018, Some palaeontologists have suggested that animals appeared much earlier than the Cambrian explosion, possibly as early as 1 billion years ago.BOOK, Campbell, Neil A., Reece, Jane B., Biology, 2005, Pearson, Benjamin Cummings, 978-0-8053-7171-0, 7th, 526, Trace fossils such as tracks and burrows found in the Tonian period may indicate the presence of triploblastic worm-like animals, roughly as large (about 5 mm wide) and complex as earthworms.JOURNAL, Seilacher, Adolf, Adolf Seilacher, Bose, Pradip K., Pfluger, Friedrich, Triploblastic animals more than 1 billion years ago: trace fossil evidence from india, Science, 282, 80–83, 2 October 1998, 10.1126/science.282.5386.80, 9756480, 5386, 1998Sci...282...80S, However, similar tracks are produced today by the giant single-celled protist Gromia sphaerica, so the Tonian trace fossils may not indicate early animal evolution.JOURNAL, Matz, Mikhail V., Frank, Tamara M., Marshall, N. Justin, Widder, Edith A., Johnsen, Sönke, Giant Deep-Sea Protist Produces Bilaterian-like Traces, Current Biology, 18, 23, 1849–54, 9 December 2008,weblink 10.1016/j.cub.2008.10.028, 2008-12-05, 19026540,weblink" title="web.archive.org/web/20081216211211weblink">weblink 16 December 2008, yes, dmy-all, NEWS, Reilly, Michael, Single-celled giant upends early evolution, MSNBC, 20 November 2008,weblink 5 December 2008, Around the same time, another line of evidence may indicate the appearance of grazing animals: the layered mats of microorganisms called stromatolites decreased in diversity, perhaps due to grazing.ENCYCLOPEDIA, Bengtson, S., 2002, Origins and early evolution of predation, The Paleontological Society Papers, 8, The fossil record of predation, Kowalewski, M., Kelley, P.H., 289–317, The Paleontological Society,weblink

Phylogeny

{{further|Lists of animals}}Animals are monophyletic, meaning they are derived from a common ancestor. Animals are sister to the Choanoflagellata, with which they form the Choanozoa.JOURNAL, 10.1111/brv.12239, 26588818, The origin of the animals and a 'Savannah' hypothesis for early bilaterian evolution, Biological Reviews, 92, 1, 446–473, 2017, Budd, Graham E, Jensen, Sören, The most basal animals, the Porifera, Ctenophora, Cnidaria, and Placozoa, have body plans that lack bilateral symmetry. Their relationships are still disputed; the sister group to all other animals could be the Porifera or the Ctenophora, which like the Porifera lack hox genes, important in body plan development.JOURNAL, Giribet, Gonzalo, Genomics and the animal tree of life: conflicts and future prospects, Zoologica Scripta, 45, 27 September 2016, 10.1111/zsc.12215, 14–21, These genes are found in the PlacozoaWEB,weblink Evolution and Development, 1 May 2012, Carnegie Institution for Science Department of Embryology, 38,weblink" title="web.archive.org/web/20140302084415weblink">weblink 2 March 2014, yes, 4 March 2018, JOURNAL, Dellaporta, Stephen, Holland, Peter, Schierwater, Bernd, Jakob, Wolfgang, Sagasser, Sven, Kuhn, Kerstin, The Trox-2 Hox/ParaHox gene of Trichoplax (Placozoa) marks an epithelial boundary, Development Genes and Evolution, 214, 4, April 2004, 10.1007/s00427-004-0390-8, 14997392, 170–175, and the higher animals, the Bilateria.JOURNAL, 10.1046/j.1525-142x.2001.003003170.x, 11440251, Animal phylogeny and the ancestry of bilaterians: Inferences from morphology and 18S rDNA gene sequences, Evolution and Development, 3, 3, 170–205, 2001, Peterson, Kevin J., Eernisse, Douglas J, 10.1.1.121.1228, JOURNAL, 10.1101/041806,weblink 25 February 2018, A catalogue of Bilaterian-specific genes – their function and expression profiles in early development, 2016, Kraemer-Eis, Andrea, Ferretti, Luca, Schiffer, Philipp, Heger, Peter, Wiehe, Thomas, 6,331 groups of genes common to all living animals have been identified; these may have arisen from a single common ancestor that lived 650 million years ago in the Precambrian. 25 of these are novel core gene groups, found only in animals; of those, 8 are for essential components of the Wnt and TGF-beta signalling pathways which may have enabled animals to become multicellular by providing a pattern for the body's system of axes (in three dimensions), and another 7 are for transcription factors including homeodomain proteins involved in the control of development.NEWS, Zimmer, Carl, Carl Zimmer, The Very First Animal Appeared Amid an Explosion of DNA,weblink 4 May 2018, The New York Times, 4 May 2018, JOURNAL, Paps, Jordi, Holland, Peter W.H., Reconstruction of the ancestral metazoan genome reveals an increase in genomic novelty,weblink 30 April 2018, Nature Communications, 9, 1730, 1730 (2018), 10.1038/s41467-018-04136-5, 29712911, 5928047, 4 May 2018, 2018NatCo...9.1730P, The phylogenetic tree (of major lineages only) indicates approximately how many millions of years ago ({{em|mya}}) the lineages split.JOURNAL, Peterson, Kevin J., Cotton, James A., Gehling, James G., Pisani, Davide, 27 April 2008, The Ediacaran emergence of bilaterians: congruence between the genetic and the geological fossil records,weblink Philosophical Transactions of the Royal Society of London B: Biological Sciences, 363, 1496, 1435–1443, 10.1098/rstb.2007.2233, 18192191, 2614224, JOURNAL, Parfrey, Laura Wegener, Lahr, Daniel J.G., Knoll, Andrew H., Katz, Laura A., 16 August 2011, Estimating the timing of early eukaryotic diversification with multigene molecular clocks,weblink Proceedings of the National Academy of Sciences, 108, 33, 13624–13629, 10.1073/pnas.1110633108, 21810989, 2011PNAS..10813624P, 3158185, WEB, Raising the Standard in Fossil Calibration,weblink Fossil Calibration Database, 3 March 2018, JOURNAL, Laumer, Christopher E., Gruber-Vodicka, Harald, Hadfield, Michael G., Pearse, Vicki B., Riesgo, Ana, Marioni, John C., Giribet, Gonzalo, 2018-03-17, Placozoa and Cnidaria are sister taxa,weblink bioRxiv, 200972, 10.1101/200972, JOURNAL, Adl, Sina M., Bass, David, Lane, Christopher E., Lukeš, Julius, Schoch, Conrad L., Smirnov, Alexey, Agatha, Sabine, Berney, Cedric, Brown, Matthew W., 2018, Revisions to the Classification, Nomenclature, and Diversity of Eukaryotes, Journal of Eukaryotic Microbiology, 66, 1, 4–119, 10.1111/jeu.12691, 30257078, {{Clade |style = font-size:80%; line-height:80%Choanozoa >sublabel1=950 mya|1={{Clade
|1=Choanoflagellata (File:Desmarella moniliformis.jpg|60 px)
|label2 =Animalia |sublabel2=760 mya
|2={{Clade
|1=Porifera (File:Reef3859 - Flickr - NOAA Photo Library.jpg|60 px)
|label2=Eumetazoa
|2={{clade
|1=Ctenophora (File:Comb jelly.jpg|60 px)
|label2=ParaHoxozoa
|sublabel2=680 mya
|2={{clade
|1={{clade
|1=Placozoa (File:Trichoplax adhaerens photograph.png|60 px)
|2=Cnidaria (File:Cauliflour Jellyfish, Cephea cephea at Marsa Shouna, Red Sea, Egypt SCUBA.jpg|60 px)
}}
|label2=Bilateria |sublabel2=Triploblasts
|2={{clade
|1=Xenacoelomorpha (File:Proporus sp.png|60 px)
|label2=Nephrozoa |sublabel2=650 mya
|2={{clade
|label1=Deuterostomia
|1={{clade

|1=Chordata (File:Cyprinus carpio3.jpg|60 px)
|2=Ambulacraria (File:Portugal 20140812-DSC01434 (21371237591).jpg|60 px)
}}
|label2 =Protostomia |sublabel2=610 mya
|2={{clade
|label1=Ecdysozoa |sublabel1=>529 mya
|1={{clade
|1=Arthropoda and allies (File:Long nosed weevil edit.jpg|60 px)
|2=Nematoda and allies (File:CelegansGoldsteinLabUNC.jpg|60 px)
}}
|label2=Spiralia
|2={{clade
|label1=Gnathifera
|1={{clade
|1=Rotifera and allies (File:Bdelloid Rotifer (cropped).jpg|50 px)
|2=Chaetognatha (File:Chaetoblack.png|60 px)
}}
|label2=Platytrochozoa |sublabel2=580 mya
|2={{clade
|1=Platyhelminthes and allies (File:Sorocelis reticulosa.jpg|60 px)
|label2=Lophotrochozoa |sublabel2=550 mya
|2={{Clade
|1=Mollusca (File:Grapevinesnail 01.jpg|60 px)
|2=Annelida and allies (File:Polychaeta (no).JPG|75 px)
}}
}}
}}
}}
}}
}}
}}
}}
}}
}}
}}{{anchor|Ctenophora.2C_Porifera.2C_Placozoa.2C_Cnidaria_and_Bilateria}}

Non-bilaterian animals

(File:Elephant-ear-sponge.jpg|thumb|upright|right|Non-bilaterians include sponges (centre) and corals (background).)Several animal phyla lack bilateral symmetry. Among these, the sponges (Porifera) probably diverged first, representing the oldest animal phylum.BOOK, Bhamrah, H.S., Juneja, Kavita, An Introduction to Porifera, 2003, Anmol Publications, 978-81-261-0675-2, 58, Sponges lack the complex organization found in most other animal phyla;BOOK, Sumich, James L., Laboratory and Field Investigations in Marine Life, 2008, Jones & Bartlett Learning, 978-0-7637-5730-4, 67, their cells are differentiated, but in most cases not organised into distinct tissues.BOOK, Jessop, Nancy Meyer, Biosphere; a study of life, 1970, Prentice-Hall, 428, They typically feed by drawing in water through pores.BOOK, Sharma, N.S., Continuity And Evolution Of Animals, 2005, Mittal Publications, 978-81-8293-018-6, 106, The Ctenophora (comb jellies) and Cnidaria (which includes jellyfish, sea anemones, and corals) are radially symmetric and have digestive chambers with a single opening, which serves as both mouth and anus.BOOK, A Living Bay: The Underwater World of Monterey Bay, 2000, University of California Press, 978-0-520-22149-9, Langstroth, Lovell, Langstroth, Libby, Newberry, Todd, 244, Animals in both phyla have distinct tissues, but these are not organised into organs.BOOK, Safra, Jacob E., The New Encyclopædia Britannica, Volume 16, 2003, Encyclopædia Britannica, 978-0-85229-961-6, 523, They are diploblastic, having only two main germ layers, ectoderm and endoderm.BOOK, Kotpal, R.L., Modern Text Book of Zoology: Invertebrates, Rastogi Publications, 978-81-7133-903-7, 184, 2012, The tiny placozoans are similar, but they do not have a permanent digestive chamber.BOOK, Barnes, Robert D., 1982, Invertebrate Zoology, Holt-Saunders International, 84–85, 978-0-03-056747-6, WEB, Introduction to Placozoa,weblink UCMP Berkeley, 10 March 2018,

Bilaterian animals

File:Bilaterian body plan.svg|thumb|upright=1.7|left|Idealised bilaterian body plan.{{efn|Compare (:File:Annelid redone w white background.svg) for a more specific and detailed model of a particular phylum with this general body plan.}} With an elongated body and a direction of movement the animal has head and tail ends. Sense organs and mouth form the basis of the head. Opposed circular and longitudinal muscles enable peristaltic motion.]]The remaining animals, the great majority—comprising some 29 phyla and over a million species—form a clade, the Bilateria. The body is triploblastic, with three well-developed germ layers, and their tissues form distinct organs. The digestive chamber has two openings, a mouth and an anus, and there is an internal body cavity, a coelom or pseudocoelom. Animals with this bilaterally symmetric body plan and a tendency to move in one direction have a head end (anterior) and a tail end (posterior) as well as a back (dorsal) and a belly (ventral); therefore they also have a left side and a right side.Having a front end means that this part of the body encounters stimuli, such as food, favouring cephalisation, the development of a head with sense organs and a mouth. Many bilaterians have a combination of circular muscles that constrict the body, making it longer, and an opposing set of longitudinal muscles, that shorten the body; these enable soft-bodied animals with a hydrostatic skeleton to move by peristalsis.JOURNAL, Quillin, K.J., Ontogenetic scaling of hydrostatic skeletons: geometric, static stress and dynamic stress scaling of the earthworm lumbricus terrestris, The Journal of Experimental Biology, 201, 12, 1871–1883, May 1998, 9600869,weblink They also have a gut that extends through the basically cylindrical body from mouth to anus. Many bilaterian phyla have primary larvae which swim with cilia and have an apical organ containing sensory cells. However, there are exceptions to each of these characteristics; for example, adult echinoderms are radially symmetric (unlike their larvae), while some parasitic worms have extremely simplified body structures.BOOK, Minelli, Alessandro, Perspectives in Animal Phylogeny and Evolution,weblink 2009, Oxford University Press, 978-0-19-856620-5, 53, BOOK,weblink Introduction to the Bilateria and the Phylum Xenacoelomorpha {{!, Triploblasty and Bilateral Symmetry Provide New Avenues for Animal Radiation |work=Invertebrates |last=Brusca |first=Richard C. |date=2016 |publisher=Sinauer Associates |pages=345–372 |isbn=978-1-60535-375-3}}Genetic studies have considerably changed zoologists' understanding of the relationships within the Bilateria. Most appear to belong to two major lineages, the protostomes and the deuterostomes.JOURNAL, Telford, Maximilian J., Resolving Animal Phylogeny: A Sledgehammer for a Tough Nut?, Developmental Cell, 14, 4, 2008, 10.1016/j.devcel.2008.03.016, 457–459, 18410719, The basalmost bilaterians are the Xenacoelomorpha.JOURNAL, Philippe, H., Brinkmann, H., Copley, R.R., Moroz, L.L., Nakano, H., Poustka, A.J., Wallberg, A., Peterson, K.J., Telford, M.J., Acoelomorph flatworms are deuterostomes related to Xenoturbella, Nature, 470, 255–258, 2011, 21307940, 10.1038/nature09676, 2011Natur.470..255P, 7333, 4025995, JOURNAL, Perseke, M., Hankeln, T., Weich, B., Fritzsch, G., Stadler, P.F., Israelsson, O., Bernhard, D., Schlegel, M., The mitochondrial DNA of Xenoturbella bocki: genomic architecture and phylogenetic analysis, Theory Biosci, 126, 1, August 2007, 35–42,weblink 18087755, 10.1007/s12064-007-0007-7, 10.1.1.177.8060, JOURNAL, Cannon, Johanna T., Vellutini, Bruno C., Smith III, Julian., Ronquist, Frederik, Jondelius, Ulf, Hejnol, Andreas, 3 February 2016, Xenacoelomorpha is the sister group to Nephrozoa,weblink Nature, 530, 7588, 89–93, 10.1038/nature16520, 3 February 2016, 26842059, 2016Natur.530...89C, {{clear}}

Protostomes and deuterostomes

{{further|Embryological origins of the mouth and anus}}File:Protovsdeuterostomes.svg|thumb|upright=1.3|right|The bilaterian gut develops in two ways. In many protostomes, the blastopore develops into the mouth, while in deuterostomedeuterostomeProtostomes and deuterostomes differ in several ways. Early in development, deuterostome embryos undergo radial cleavage during cell division, while many protostomes (the Spiralia) undergo spiral cleavage.JOURNAL, Valentine, James W., July 1997, Cleavage patterns and the topology of the metazoan tree of life, PNAS, 94, 8001–8005, 1997PNAS...94.8001V, 10.1073/pnas.94.15.8001, 9223303, 21545, 15, Animals from both groups possess a complete digestive tract, but in protostomes the first opening of the embryonic gut develops into the mouth, and the anus forms secondarily. In deuterostomes, the anus forms first while the mouth develops secondarily.BOOK, Peters, Kenneth E., Walters, Clifford C., Moldowan, J. Michael, The Biomarker Guide: Biomarkers and isotopes in petroleum systems and Earth history, 2, 2005, Cambridge University Press, 978-0-521-83762-0, 717, BOOK, Hejnol, A., Martindale, M.Q.,weblink The mouth, the anus, and the blastopore – open questions about questionable openings, Animal Evolution – Genomes, Fossils, and Trees, Telford, M.J., Littlewood, D.J., 2009, Oxford University Press, 978-0-19-957030-0, 33–40, Most protostomes have schizocoelous development, where cells simply fill in the interior of the gastrula to form the mesoderm. In deuterostomes, the mesoderm forms by enterocoelic pouching, through invagination of the endoderm.BOOK, Safra, Jacob E., The New Encyclopædia Britannica, Volume 1; Volume 3, 2003, Encyclopædia Britannica, 978-0-85229-961-6, 767, The main deuterostome phyla are the Echinodermata and the Chordata.BOOK, Hyde, Kenneth, Zoology: An Inside View of Animals, 2004, Kendall Hunt, 978-0-7575-0997-1, 345, Echinoderms are exclusively marine and include starfish, sea urchins, and sea cucumbers.BOOK, Alcamo, Edward, Biology Coloring Workbook, 1998, The Princeton Review, 978-0-679-77884-4, 220, The chordates are dominated by the vertebrates (animals with backbones),BOOK, Holmes, Thom, The First Vertebrates, Infobase Publishing, 2008, 978-0-8160-5958-4, 64, which consist of fishes, amphibians, reptiles, birds, and mammals.BOOK, Rice, Stanley A., Encyclopedia of evolution, Infobase Publishing, 2007, 75, 978-0-8160-5515-9, The deuterostomes also include the Hemichordata (acorn worms).BOOK, Tobin, Allan J., Dusheck, Jennie, Asking about life, 2005, Cengage Learning, 978-0-534-40653-0, 497, JOURNAL, Hemichordate genomes and deuterostome origins,weblink Nature, 26 November 2015, 459–465, 527, 7579, 10.1038/nature16150, Oleg, Simakov, Takeshi, Kawashima, Ferdinand, Marlétaz, Jerry, Jenkins, Ryo, Koyanagi, Therese, Mitros, Kanako, Hisata, Jessen, Bredeson, Eiichi, Shoguchi, 26580012, 4729200, 2015Natur.527..459S,

Ecdysozoa

File:Anax Imperator 2(loz).JPG|thumb|upright|Ecdysis: a dragonfly has emerged from its dry exuviae and is expanding its wings. Like other arthropods, its body is divided into segments.]]The Ecdysozoa are protostomes, named after their shared trait of ecdysis, growth by moulting.BOOK, Dawkins, Richard, Richard Dawkins, The Ancestor's Tale: A Pilgrimage to the Dawn of Evolution, 2005, Houghton Mifflin Harcourt, 978-0-618-61916-0, 381, They include the largest animal phylum, the Arthropoda, which contains insects, spiders, crabs, and their kin. All of these have a body divided into repeating segments, typically with paired appendages. Two smaller phyla, the Onychophora and Tardigrada, are close relatives of the arthropods and share these traits. The ecdysozoans also include the Nematoda or roundworms, perhaps the second largest animal phylum. Roundworms are typically microscopic, and occur in nearly every environment where there is water;BOOK, Prewitt, Nancy L., Underwood, Larry S., Surver, William, BioInquiry: making connections in biology, 2003, John Wiley, 978-0-471-20228-8, 289, some are important parasites.BOOK, Parasites in social insects, 1998, Princeton University Press, 978-0-691-05924-2, Schmid-Hempel, Paul, 75, Smaller phyla related to them are the Nematomorpha or horsehair worms, and the Kinorhyncha, Priapulida, and Loricifera. These groups have a reduced coelom, called a pseudocoelom.BOOK, Miller, Stephen A., Harley, John P., Zoology,weblink 2006, McGraw-Hill Higher Education, 173,

Spiralia

File:Spiral cleavage in Trochus.png|thumb|left|upright=1.6|Spiral cleavageSpiral cleavageThe Spiralia are a large group of protostomes that develop by spiral cleavage in the early embryo.JOURNAL, 10781038, 34316, 122407, 2000PNAS...97.4434S, 10.1073/pnas.97.9.4434, Evolution of the bilaterian body plan: What have we learned from annelids?, Proceedings of the National Academy of Sciences, 97, 9, 4434–4437, 2000, Shankland, M., Seaver, E.C., The Spiralia's phylogeny has been disputed, but it contains a large clade, the superphylum Lophotrochozoa, and smaller groups of phyla such as the Rouphozoa which includes the gastrotrichs and the flatworms. All of these are grouped as the Platytrochozoa, which has a sister group, the Gnathifera, which includes the rotifers.JOURNAL, Struck, Torsten H., Wey-Fabrizius, Alexandra R., Golombek, Anja, Hering, Lars, Weigert, Anne, Bleidorn, Christoph, Klebow, Sabrina, Iakovenko, Nataliia, Hausdorf, Bernhard, Petersen, Malte, Kück, Patrick, Herlyn, Holger, Hankeln, Thomas, Platyzoan Paraphyly Based on Phylogenomic Data Supports a Noncoelomate Ancestry of Spiralia, Molecular Biology and Evolution, 31, 7, 2014, 10.1093/molbev/msu143, 1833–1849, 24748651, JOURNAL, Fröbius, Andreas C., Funch, Peter, April 2017, Rotiferan Hox genes give new insights into the evolution of metazoan bodyplans,weblink Nature Communications, 8, 1, 9, 10.1038/s41467-017-00020-w, 28377584, 5431905, 2017NatCo...8....9F, The Lophotrochozoa includes the molluscs, annelids, brachiopods, nemerteans, bryozoa and entoprocts.JOURNAL, Hervé, Philippe, Lartillot, Nicolas, Brinkmann, Henner, May 2005, Multigene Analyses of Bilaterian Animals Corroborate the Monophyly of Ecdysozoa, Lophotrochozoa, and Protostomia, Molecular Biology and Evolution, 22, 5, 1246–1253, 10.1093/molbev/msi111, 15703236, WEB, Introduction to the Lophotrochozoa {{!, Of molluscs, worms, and lophophores… |url=http://www.ucmp.berkeley.edu/phyla/lophotrochozoa.html |publisher=UCMP Berkeley |accessdate=28 February 2018}} The molluscs, the second-largest animal phylum by number of described species, includes snails, clams, and squids, while the annelids are the segmented worms, such as earthworms, lugworms, and leeches. These two groups have long been considered close relatives because they share trochophore larvae.JOURNAL, Giribet, G., Distel, D.L., Polz, M., Sterrer, W., Wheeler, W.C., 2000, Triploblastic relationships with emphasis on the acoelomates and the position of Gnathostomulida, Cycliophora, Plathelminthes, and Chaetognatha: a combined approach of 18S rDNA sequences and morphology, Syst Biol, 49, 3, 539–562, 10.1080/10635159950127385, 12116426, JOURNAL, Phylogenetic Relationships of Annelids, Molluscs, and Arthropods Evidenced from Molecules and Morphology, Journal of Molecular Evolution, 43, 3, 207–215, September 1996, 10.1007/PL00006079, 8703086, Kim, Chang Bae, Moon, Seung Yeo, Gelder, Stuart R., Kim, Won,

History of classification

{{further|Taxonomy (biology)|History of zoology (through 1859)|History of zoology since 1859}}File:Jean-Baptiste de Lamarck.jpg|thumb|upright|left|Jean-Baptiste de LamarckJean-Baptiste de LamarckIn the classical era, Aristotle divided animals,{{efn|In his History of Animals and Parts of Animals.}} based on his own observations, into those with blood (roughly, the vertebrates) and those without. The animals were then arranged on a scale from man (with blood, 2 legs, rational soul) down through the live-bearing tetrapods (with blood, 4 legs, sensitive soul) and other groups such as crustaceans (no blood, many legs, sensitive soul) down to spontaneously-generating creatures like sponges (no blood, no legs, vegetable soul). Aristotle was uncertain whether sponges were animals, which in his system ought to have sensation, appetite, and locomotion, or plants, which did not: he knew that sponges could sense touch, and would contract if about to be pulled off their rocks, but that they were rooted like plants and never moved about.BOOK, Leroi, Armand Marie, Armand Marie Leroi, The Lagoon: How Aristotle Invented Science, Aristotle's Lagoon, Bloomsbury, 2014, 978-1-4088-3622-4, 111–119, 270–271, In 1758, Carl Linnaeus created the first hierarchical classification in his Systema Naturae.BOOK, Linnaeus, Carl, Carl Linnaeus, Systema naturae per regna tria naturae :secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis., 10th edition of Systema Naturae, 10th, Holmiae (Laurentii Salvii), 1758,weblink 22 September 2008, Latin,weblink" title="web.archive.org/web/20081010032456weblink">weblink 10 October 2008, no, In his original scheme, the animals were one of three kingdoms, divided into the classes of Vermes, Insecta, Pisces, Amphibia, Aves, and Mammalia. Since then the last four have all been subsumed into a single phylum, the Chordata, while his Insecta (which included the crustaceans and arachnids) and Vermes have been renamed or broken up. The process was begun in 1793 by Jean-Baptiste de Lamarck, who called the Vermes une espèce de chaos (a chaotic mess){{efn|The prefix une espèce de is pejorative.WEB, Espèce de,weblink Reverso Dictionnnaire, 1 March 2018, }} and split the group into three new phyla, worms, echinoderms, and polyps (which contained corals and jellyfish). By 1809, in his Philosophie Zoologique, Lamarck had created 9 phyla apart from vertebrates (where he still had 4 phyla: mammals, birds, reptiles, and fish) and molluscs, namely cirripedes, annelids, crustaceans, arachnids, insects, worms, radiates, polyps, and infusorians.BOOK, Gould, Stephen Jay, Stephen Jay Gould, The Lying Stones of Marrakech,weblink 2011, Harvard University Press, 978-0-674-06167-5, 130–134, In his 1817 Le Règne Animal, Georges Cuvier used comparative anatomy to group the animals into four embranchements ("branches" with different body plans, roughly corresponding to phyla), namely vertebrates, molluscs, articulated animals (arthropods and annelids), and zoophytes (radiata) (echinoderms, cnidaria and other forms).BOOK, De Wit, Hendrik C.D., Histoire du Développement de la Biologie, Volume III, Presses Polytechniques et Universitaires Romandes, 1994, 94–96, 978-2-88074-264-5, This division into four was followed by the embryologist Karl Ernst von Baer in 1828, the zoologist Louis Agassiz in 1857, and the comparative anatomist Richard Owen in 1860.In 1874, Ernst Haeckel divided the animal kingdom into two subkingdoms: Metazoa (multicellular animals, with five phyla: coelenterates, echinoderms, articulates, molluscs, and vertebrates) and Protozoa (single-celled animals), including a sixth animal phylum, sponges.BOOK, Haeckel, Ernst, Ernst Haeckel, Anthropogenie oder Entwickelungsgeschichte des menschen, 1874, 202, German, BOOK, Valentine, James W., On the Origin of Phyla,weblink 2004, University of Chicago Press, 978-0-226-84548-7, 7–8, The protozoa were later moved to the former kingdom Protista, leaving only the Metazoa as a synonym of Animalia.BOOK, Hutchins, Michael, Grzimek's Animal Life Encyclopedia, 2003, 2nd, Gale, 978-0-7876-5777-2, 3,

In human culture

File:Carni bovine macellate.JPG|thumb|upright|Sides of beef in a slaughterhouseslaughterhouseThe human population exploits a large number of other animal species for food, both of domesticated livestock species in animal husbandry and, mainly at sea, by hunting wild species.WEB,weblink Fisheries and Aquaculture, FAO, 8 July 2016, Marine fish of many species are caught commercially for food. A smaller number of species are farmed commercially.BOOK, Helfman, Gene S., Fish Conservation: A Guide to Understanding and Restoring Global Aquatic Biodiversity and Fishery Resources, 2007, Island Press, 978-1-59726-760-1, 11, WEB, World Review of Fisheries and Aquaculture,weblink fao.org, FAO, 13 August 2015, Invertebrates including cephalopods, crustaceans, and bivalve or gastropod molluscs are hunted or farmed for food.JOURNAL, Shellfish climbs up the popularity ladder, Seafood Business,weblinkweblink" title="web.archive.org/web/20121105143157weblink">weblink yes, 2012-11-05, 8 July 2016, January 2002, Chickens, cattle, sheep, pigs and other animals are raised as livestock for meat across the world.JOURNAL, Graphic detail Charts, maps and infographics. Counting chickens, The Economist,weblink 23 June 2016, 27 July 2011, WEB, Cattle Today,weblink Breeds of Cattle at CATTLE TODAY, Cattle-today.com, 15 October 2013, WEB, Lukefahr, S.D., Cheeke, P.R., Rabbit project development strategies in subsistence farming systems,weblink Food and Agriculture Organization, 23 June 2016, Animal fibres such as wool are used to make textiles, while animal sinews have been used as lashings and bindings, and leather is widely used to make shoes and other items. Animals have been hunted and farmed for their fur to make items such as coats and hats.WEB, Animals Used for Clothing,weblink PETA, 8 July 2016, WEB, Ancient fabrics, high-tech geotextiles,weblink Natural Fibres, 8 July 2016, Dyestuffs including carmine (cochineal),WEB,weblink Cochineal and Carmine, Major colourants and dyestuffs, mainly produced in horticultural systems, FAO, June 16, 2015, WEB,weblink Guidance for Industry: Cochineal Extract and Carmine, FDA, 6 July 2016, shellac,NEWS, How Shellac Is Manufactured,weblink 17 July 2015, The Mail (Adelaide, SA : 1912–1954), 18 Dec 1937, JOURNAL, Pearnchob, N., Siepmann, J., Bodmeier, R., 2003, Pharmaceutical applications of shellac: moisture-protective and taste-masking coatings and extended-release matrix tablets, Drug Development and Industrial Pharmacy, 29, 8, 925–938, 14570313, 10.1081/ddc-120024188, and kermesBOOK, Barber, E.J.W., Prehistoric Textiles, 1991, Princeton University Press, 978-0-691-00224-8, 230–231, BOOK, Munro, John H., Medieval Woollens: Textiles, Technology, and Organisation, Jenkins, David, 2003, The Cambridge History of Western Textiles, Cambridge University Press, 978-0-521-34107-3, 214–215, have been made from the bodies of insects. Working animals including cattle and horses have been used for work and transport from the first days of agriculture.BOOK, Pond, Wilson G., Encyclopedia of Animal Science,weblink 2004, CRC Press, 978-0-8247-5496-9, 248–250, Animals such as the fruit fly Drosophila melanogaster serve a major role in science as experimental models.WEB, Genetics Research,weblink Animal Health Trust, 24 June 2016, WEB, Drug Development,weblink Animal Research.info, 24 June 2016, WEB, Animal Experimentation,weblink BBC, 8 July 2016, WEB, EU statistics show decline in animal research numbers,weblink Speaking of Research, 2013, January 24, 2016, Animals have been used to create vaccines since their discovery in the 18th century.WEB, Vaccines and animal cell technology,weblink Animal Cell Technology Industrial Platform, 9 July 2016, Some medicines such as the cancer drug Yondelis are based on toxins or other molecules of animal origin.WEB, Medicines by Design,weblink National Institute of Health, 9 July 2016, File:Hebbuz.JPG|thumb|left|A gun doggun dogPeople have used hunting dogs to help chase down and retrieve animals,BOOK, Fergus, Charles, Gun Dog Breeds, A Guide to Spaniels, Retrievers, and Pointing Dogs, The Lyons Press, 2002, 978-1-58574-618-7, and birds of prey to catch birds and mammals,WEB, History of Falconry,weblink The Falconry Centre, 22 April 2016, while tethered cormorants have been used to catch fish.BOOK, King, Richard J., The Devil's Cormorant: A Natural History,weblink 2013, University of New Hampshire Press, 978-1-61168-225-0, 9, Poison dart frogs have been used to poison the tips of blowpipe darts.WEB,weblink AmphibiaWeb – Dendrobatidae, AmphibiaWeb, 2008-10-10, WEB,weblink Dendrobatidae, 9 July 2016, Heying, H., 2003, Animal Diversity Web, A wide variety of animals are kept as pets, from invertebrates such as tarantulas and octopuses, insects including praying mantises,WEB, Other bugs,weblink Keeping Insects, 8 July 2016, reptiles such as snakes and chameleons,WEB, Kaplan, Melissa, So, you think you want a reptile?,weblink Anapsid.org, 8 July 2016, and birds including canaries, parakeets, and parrotsWEB, Pet Birds,weblink PDSA, 8 July 2016, all finding a place. However, the most kept pet species are mammals, namely dogs, cats, and rabbits.WEB,weblink Animals in Healthcare Facilities, 2012, yes,weblink" title="web.archive.org/web/20160304102728weblink">weblink 4 March 2016, WEB, The Humane Society of the United States, U.S. Pet Ownership Statistics,weblink 27 April 2012, WEB, USDA, U.S. Rabbit Industry profile,weblink 10 July 2013, yes,weblink" title="web.archive.org/web/20131020161216weblink">weblink 20 October 2013, There is a tension between the role of animals as companions to humans, and their existence as individuals with rights of their own.JOURNAL, The Role of Animals in Human Society, Plous, S., 1993, 10.1111/j.1540-4560.1993.tb00906.x, Journal of Social Issues, 49, 1, 1–9, A wide variety of terrestrial and aquatic animals are hunted for sport.BOOK, Hummel, Richard, Hunting and Fishing for Sport: Commerce, Controversy, Popular Culture, 1994, Popular Press, 978-0-87972-646-1, File:Alexander Coosemans - Still Life with Lobster and Oysters.jpg|thumb|Artistic vision: Still Life with Lobster and Oysters by Alexander CoosemansAlexander CoosemansAnimals have been the subjects of art from the earliest times, both historical, as in Ancient Egypt, and prehistoric, as in the cave paintings at Lascaux. Major animal paintings include Albrecht Dürer's 1515 The Rhinoceros, and George Stubbs's c. 1762 horse portrait Whistlejacket.NEWS, Jones, Jonathan, The top 10 animal portraits in art,weblink 24 June 2016, The Guardian, 27 June 2014, Insects, birds and mammals play roles in literature and film,JOURNAL, Paterson, Jennifer, Animals in Film and Media,weblink Oxford Bibliographies, 24 June 2016, 29 October 2013, 10.1093/obo/9780199791286-0044, such as in giant bug movies.BOOK, Gregersdotter, Katarina, Höglund, Johan, Hållén, Nicklas, Animal Horror Cinema: Genre, History and Criticism,weblink 2016, Springer, 978-1-137-49639-3, 147, BOOK, Warren, Bill, Thomas, Bill, Keep Watching the Skies!: American Science Fiction Movies of the Fifties, The 21st Century Edition,weblink 2009, McFarland, 978-1-4766-2505-8, 32, BOOK, Crouse, Richard, Son of the 100 Best Movies You've Never Seen,weblink 2008, ECW Press, 978-1-55490-330-6, 200, Animals including insects and mammals feature in mythology and religion. In both Japan and Europe, a butterfly was seen as the personification of a person's soul,BOOK, Hearn, Lafcadio, Lafcadio Hearn, 1904, Kwaidan: Stories and Studies of Strange Things, Kwaidan: Stories and Studies of Strange Things, Dover, 978-0-486-21901-1, JOURNAL,weblink Butterfly, Encyclopedia of Diderot and d'Alembert, 10 July 2016, January 2011, Louis, Chevalier de Jaucourt (Biography), Hutchins, M., Arthur V. Evans, Rosser W. Garrison and Neil Schlager (Eds) (2003) Grzimek's Animal Life Encyclopedia, 2nd edition. Volume 3, Insects. Gale, 2003. while the scarab beetle was sacred in ancient Egypt.BOOK, Ben-Tor, Daphna, Scarabs, A Reflection of Ancient Egypt, Jerusalem, Israel Museum, 1989, 978-965-278-083-6, 8, Among the mammals, cattle,NEWS, Biswas, Soutik, Why the humble cow is India's most polarising animal,weblink BBC, 9 July 2016, BBC News, 2015-10-15, deer,WEB, Deer,weblink Trees for Life (Scotland), Trees for Life, 23 June 2016, horses,BOOK, Hayagrīva: The Mantrayānic Aspect of Horse-cult in China and Japan, Brill Archive, 9, Robert Hans van Gulik, lions,WEB, Grainger, Richard, Lion Depiction across Ancient and Modern Religions,weblink Alert, 6 July 2016, 24 June 2012, yes,weblink 23 September 2016, bats,BOOK, Read, Kay Almere, Gonzalez, Jason J., 2000, Mesoamerican Mythology, Oxford University Press, 132–134, bears,JOURNAL, Wunn, Ina, January 2000, Beginning of Religion,weblink Numen, 47, 4, 417–452, 10.1163/156852700511612, and wolvesBOOK, McCone, Kim R., Hund, Wolf, und Krieger bei den Indogermanen, Meid, W., Studien zum indogermanischen Wortschatz, Innsbruck, 1987, 101–154, are the subjects of myths and worship. The signs of the Western and Chinese zodiacs are based on animals.BOOK, Lau, Theodora, The Handbook of Chinese Horoscopes, 2–8, 30–35, 60–64, 88–94, 118–124, 148–153, 178–184, 208–213, 238–244, 270–278, 306–312, 338–344, Souvenir Press, New York, 2005, BOOK, Tester, S. Jim, A History of Western Astrology,weblink 1987, Boydell & Brewer, 978-0-85115-446-6, 31–33 and passim,

See also

{{Wikipedia books}} {{clear}}

Notes

{{Notelist}}

References

{{Reflist}}

External links

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