Animalia

Superregnum: Eukaryota
Cladus: Unikonta
Cladus: Opisthokonta
Cladus: Holozoa
Regnum: Animalia
Subregna (2): Eumetazoa – Parazoa
Overview of phyla (36)

Acanthocephala – Annelida – Arthropoda – Brachiopoda – Bryozoa – Cephalorhyncha – Chaetognatha – Chordata – Cnidaria – Ctenophora – Cycliophora – Echinodermata – Echiura – Gastrotricha – Gnathostomulida – Hemichordata – Kamptozoa – Kinorhyncha – Loricifera – Micrognathozoa – Mollusca – Myxozoa – Nematoda – Nematomorpha – Nemertea – Onychophora – Orthonectida – Phoronida – Placozoa – Platyhelminthes – Porifera – Rhombozoa – Rotifera – Sipuncula – Tardigrada – †Vendobionta – Xenacoelomorpha
†Animalia incertae sedis
Source(s) of checklist:
Catalogue of Life: 2014 Annual Checklist is followed for pragmatic reasons, though the following alternative phyla deserve consideration: Dicyemida – Entoprocta – Monoblastozoa – Myzostomida – Priapulida – †Trilobozoa
Name

Animalia Linnaeus, 1758 emend.
Synonyms

Metazoa Haeckel, 1874
Zooaea Barkley, 1939
Gastrobionta Rothmaler, 1948
Euanimalia Barkley, 1949

Classifications

Main page: Animalia (classifications).

References
Biodiversity

Zhang, Z.-Q. (ed.) 2011. Animal biodiversity: an outline of higher-level classification and survey of taxonomic richness. Zootaxa 3148: 1–237. Open access. Reference page
Zhang, Z.-Q. (ed.) 2013: Animal biodiversity: an outline of higher-level classification and survey of taxonomic richness (Addenda 2013). Zootaxa 3703(1): 1–82. DOI: 10.11646/zootaxa.3703.1.1 Reference page.

Animal biodiversity publishing

Blagoderov, V. et al. 2010. Streamlining taxonomic publication: a working example with Scratchpads and ZooKeys. ZooKeys 50: 17–28. DOI: 10.3897/zookeys.50.539
Penev, L. et al. 2010. Editorial. Taxonomy shifts up a gear: New publishing tools to accelerate biodiversity research. ZooKeys 50: i–iv. DOI: 10.3897/zookeys.50.543
Penev, L. et al. 2010. Semantic tagging of and semantic enhancements to systematics papers: ZooKeys working examples. ZooKeys 50: 1–16. DOI: 10.3897/zookeys.50.538
Penev, L. et al. 2011. Interlinking journal and wiki publications through joint citation: Working examples from ZooKeys and Plazi on Species-ID. ZooKeys 90: 1–12. DOI: 10.3897/zookeys.90.1369
Smith, V. & Penev, L. (eds.) 2011. e-Infrastructures for data publishing in biodiversity science. ZooKeys 150 contents
Valdecasas, A.G. 2011. An index to evaluate the quality of taxonomic publications. Zootaxa 2925: 57–62. Preview PDF
Zhang, Z.-Q. 2011. Describing unexplored biodiversity: Zootaxa in the International Year of Biodiversity. Zootaxa 2768: 1–4. Preview PDF
Zhang, Z.-Q. 2011. Accelerating biodiversity descriptions and transforming taxonomic publishing: the first decade of Zootaxa. Zootaxa 2896: 1–7. Preview PDF

Methodology in zoological taxonomy

Assis, L.C.S., De Carvalho, M.R. & Wheeler, Q.D. 2011. Homoplasy: from detecting pattern to determining process in evolution, but with a secondary role for morphology? Zootaxa 2984: 67–68. Preview (PDF)
Brown, B.V. 2013. Automating the "Material examined" section of taxonomic papers to speed up species descriptions. Zootaxa 3683(3): 297–299. DOI: 10.11646/zootaxa.3683.3.8 Reference page.
Chakrabarty, P. 2010. Genetypes: a concept to help integrate molecular phylogenetics and taxonomy. Zootaxa 2632: 67–68. Preview PDF
Coleman, C.O., Lowry, J.K. & Macfarlane, T. 2010. DELTA for beginners. An introduction into the taxonomy software package DELTA. ZooKeys, 45: 1–75. DOI: 10.3897/zookeys.45.263
Cruickshank, R.H. & Munck, L. 2011. It’s barcoding Jim, but not as we know it. Zootaxa 2933: 55–56. Preview PDF
Ebach, M.C. 2011. Taxonomy and the DNA Barcoding Enterprise. Zootaxa 2742: 67–68. Preview PDF
Faith, D.P. et al. 2012. Corroboration assessments and recent progress towards integrative systematics: a reply to Farris and Carpenter. Zootaxa 3235: 65–68. Preview (PDF)
Farris, J.S. & Carpenter, J.M. 2012. Faith et al. 2011. "corroboration assessment" leads to verificationism. Zootaxa 3235: 62–64. Preview (PDF)
Maddison, D.R., Schulz, K.-S. & Maddison, W.P. 2007. The Tree of Life Web Project. Pp. 19–40 in: Zhang, Z.-Q. & Shear, W.A. (eds.) Linnaeus tercentenary: progress in invertebrate taxonomy. Zootaxa 1668: 1–766. Abstract & excerpt (PDF) PDF
Minelli, A. 2007. Invertebrate taxonomy and evolutionary developmental biology. Pp. 55–60 in: Zhang, Z.-Q. & Shear, W.A. (eds.) Linnaeus tercentenary: progress in invertebrate taxonomy. Zootaxa 1668: 1–766. Abstract & excerpt (PDF) PDF
Mitchell, A. 2011. DNA barcoding is useful for taxonomy: a reply to Ebach. Zootaxa 2772: 67–68. Preview PDF
Rodman, J.E. 2007. Reflections on PEET, the Partnerships for Enhancing Expertise in Taxonomy. Pp. 41–46 in: Zhang, Z.-Q. & Shear, W.A. (eds.) Linnaeus tercentenary: progress in invertebrate taxonomy. Zootaxa 1668: 1–766. Abstract & excerpt (PDF) PDF
Rodríguez-Fernández, J.I. et al. 2011. Barcoding without DNA? Species identification using near infrared spectroscopy. Zootaxa 2933: 46–54. Preview
Rogers, D.C. 2012. Taxonomic certification versus the scientific method. Zootaxa 3257: 66–68. Preview (PDF)
Santos, L.M. & Faria, L.R.R. 2011. The taxonomy’s new clothes: a little more about the DNA-based taxonomy. Zootaxa 3025: 66–68. Preview PDF
Stevens, M.I., Porco, D., D’Haese, C.A. & Deharveng, L. 2011. Comment on "Taxonomy and the DNA Barcoding Enterprise" by Ebach (2011). Zootaxa 2838: 85–88. Preview PDF
Stribling, J. et al. 2012: “Taxonomic certification versus the scientific method”: a rebuttal of Rogers (2012). Zootaxa 3359: 65–68. Preview PDF [erratum in Zootaxa 3383: 14–14. Preview PDF (2012)] Reference page.
Wheeler, Q.D. 2007. Invertebrate systematics or spineless taxonomy? Pp. 10–18 in: Zhang, Z.-Q. & Shear, W.A. (eds.) Linnaeus tercentenary: progress in invertebrate taxonomy. Zootaxa 1668: 1–766. Abstract & excerpt (PDF) PDF
Wilkins, J.S. 2011. Philosophically speaking, how many species concepts are there? Zootaxa 2765: 58–60. Preview (PDF)
Winston, J.E. 2007. Archives of a small planet: The significance of museum collections and museum-based research in invertebrate taxonomy. Pp. 47–54 in: Zhang, Z.-Q. & Shear, W.A. (eds.) Linnaeus tercentenary: progress in invertebrate taxonomy. Zootaxa 1668: 1–766. Abstract & excerpt (PDF) PDF

Phylogeny

Baurain, D., Brinkmann, H. & Philippe, H. 2007. Lack of Resolution in the Animal Phylogeny: Closely Spaced Cladogeneses or Undetected Systematic Errors? Molecular biology and evolution 24: 6–9. DOI: 10.1093/molbev/msl137
Bourlat, S.J., Nielsen, C., Economou, A.D. & Telford, M.J. 2008. Testing the new animal phylogeny: a phylum level molecular analysis of the animal kingdom. Molecular phylogenetics and evolution 49: 23–31. DOI: 10.1016/j.ympev.2008.07.008 PDF
DeSalle, R. & Schierwater, B. 2008. An even "newer" animal phylogeny. BioEssays 30: 1043–1047. DOI: 10.1002/bies.20842 PDF
Dunn, C.W. et al. 2008. Broad phylogenomic sampling improves resolution of the animal tree of life. Nature 452: 745–749. DOI: 10.1038/nature06614
Edgecombe, G.D. et al. 2011. Higher-level metazoan relationships: recent progress and remaining questions. Organisms diversity & evolution 11(2): 151–172. DOI: 10.1007/s13127-011-0044-4
Giribet, G. et al. 2007. A modern look at the Animal Tree of Life. Pp. 61–79 in: Zhang, Z.-Q. & Shear, W.A. (eds.) Linnaeus tercentenary: progress in invertebrate taxonomy. Zootaxa 1668: 1–766. Abstract & excerpt (PDF) PDF
Glenner, H., Hansen, A.J., Sørensen, M.V., Ronquist, F., Huelsenbeck, J.P. & Willerslev, E. 2004. Bayesian inference of the metazoan phylogeny: a combined molecular and morphological approach. Current biology 14: 1644–1649. DOI: 10.1016/j.cub.2004.09.027
Halanych, K.M. 2004. The new view of animal phylogeny. Annual review of ecology, evolution, and systematics 35: 229–256. DOI: 10.1146/annurev.ecolsys.35.112202.130124 PDF PDF
Jenner, R.A. 2004. Towards a phylogeny of the Metazoa: evaluating alternative phylogenetic positions of Platyhelminthes, Nemertea, and Gnathostomulida, with a critical reappraisal of cladistic characters. Contributions to zoology 73(1–2): 3–163.
Leys, S.P. & Eerkes-Medrano, D. 2005. Gastrulation in calcareous sponges: in search of Haeckel’s Gastraea. Integrative & comparative biology 45: 342–351. DOI: 10.1093/icb/45.2.342 PDF
Medina, M., Collins, A.G., Silberman, J.D. & Sogin, M.L. 2001. Evaluating hypotheses of basal animal phylogeny using complete sequences of large and small subunit rRNA. PNAS 98: 9707–9712. DOI: 10.1073/pnas.171316998 JSTOR PubMed
Nielsen, C. 2001. Animal evolution: interrelationships of the living phyla (2nd edition). Oxford University Press, New York. ISBN 0198506821 ISBN 9780198506829
Schierwater, B.& DeSalle, R. 2007. Can we ever identify the Urmetazoan? Integrative and comparative biology 47: 670–676. DOI: 10.1093/icb/icm040
Schierwater, B. et al. 2009: Concatenated Analysis Sheds Light on Early Metazoan Evolution and Fuels a Modern “Urmetazoon” Hypothesis. PLoS Biol 7(1): e1000020. DOI: 10.1371/journal.pbio.1000020
Schmidt-Rhaesa, A. 2003. Old trees, new trees: is there any progress? Zoology 106: 291–301. DOI: 10.1078/0944-2006-00128
Sorensen, M.V., Funch, P., Willerslev, E., Hansen, A.J. & Olesen J. 2000. On the phylogeny of the metazoa in the light of Cycliophora and Micrognathozoa. Zoologischer anzeiger 239: 297–318.
Syed, T., Gudo, M. & Gutmann, M. 2007. The new animal phylogeny – dilemma or progress? Denisia (20): 295–312.
Telford, M.J. 2006. Animal phylogeny. Current biology 16: R981-R985. DOI: 10.1016/j.cub.2006.10.048
Zrzavý, J. 2002. Gastrotricha and metazoan phylogeny. Zoologica scripta 32: 61–81. DOI: 10.1046/j.1463-6409.2003.00104.x

Zoological nomenclature/terminology

Anon. 2010. Official Lists and Indexes of Names in Zoology Updated March 2010
Bour, R. 2010. Constant Duméril’s Zoologie Analytique was published in 1805. Bionomina 1: 56–57. Preview (PDF) PDF
Carlos, C.J. & Voisin, J.-f. 2009. A few remarks on the proposed amendment of the International Code of Zoological Nomenclature to expand and refine methods of publication. Zootaxa 2198: 67–68. Abstract & excerpt (PDF)
Dubois, A. 2007. Nomina zoologica linnaeana. Pp. 81–106 in: Zhang, Z.-Q. & Shear, W.A. (eds.) Linnaeus tercentenary: progress in invertebrate taxonomy. Zootaxa 1668: 1–766. Abstract & excerpt (PDF)
Dubois, A. 2008. Authors of zoological publications and nomina are signatures, not persons. Zootaxa 1771: 63–68. Abstract & excerpt (PDF)
Dubois, A. 2009. Incorporation of nomina of higher-ranked taxa into the International Code of Zoological Nomenclature: the nomenclatural status of class-series zoological nomina published in a non-Latinized form. Zootaxa 2106: 1–12. Abstract & excerpt (PDF)
Dubois, A. 2010. Retroactive changes should be introduced in the Code only with great care: problems related to the spellings of nomina. Zootaxa 2426: 1–42. Preview (PDF) PDF
Dubois, A. 2010. Bionomina, a forum for the discussion of nomenclatural and terminological issues in biology. Bionomina 1: 1–10. Preview (PDF) PDF
Dubois, A. 2011. The International Code of Zoological Nomenclature must be drastically improved before it is too late. Bionomina 2: 1–104. Preview PDF
Dubois, A. 2012. The distinction between introduction of a new nomen and subsequent use of a previously introduced nomen in zoological nomenclature. Bionomina 5: 57–80. Preview (PDF)
Dubois, A., Minelli, A. & Zhang, Z.-Q. 2011. Recommendations about nomenclature for papers submitted to Zootaxa. Zootaxa 2943: 58–62. Preview PDF
Dubois, A. et al. 2013. Nomenclatural and taxonomic problems related to the electronic publication of new nomina and nomenclatural acts in zoology, with brief comments on optical discs and on the situation in botany. Zootaxa 3735(1): 1–94. DOI: 10.11646/zootaxa.3735.1.1 Reference page.
Flann, C. 2011. BioCode: third time lucky? Zootaxa 2874: 38–40. Preview (PDF)
Hedges, S.B. 2011. On the use of high-level taxonomic names. Zootaxa 2867: 67–68. Preview PDF
Hoquet, T. 2010. Why terms matter to biological theories: the term “origin” as used by Darwin. Bionomina 1: 58–60. ISSN: 1179-7649 (print edition) ISSN: 1179-7657 (online edition) Preview (PDF) PDF
ICZN 1987: Official Lists and Indexes of Names and Works in Zoology. London: ICZN. ISBN: 0853010048
ICZN 2012. Amendment of Articles 8, 9, 10, 21 and 78 of the International Code of Zoological Nomenclature to expand and refine methods of publication. Zootaxa 3450: 1–7. Preview (PDF). Full paper (PDF). Reference page.
ICZN 2012. Amendment of Articles 8, 9, 10, 21 and 78 of the International Code of Zoological Nomenclature to expand and refine methods of publication. ZooKeys 219: 1–10. DOI: 10.3897/zookeys.219.3944 Reference page.
Kuhn, J.H. & Wahl-Jensen, V. 2010. Being obsessive-compulsive about terminology and nomenclature is not a vice, but a virtue. Bionomina 1: 11–14. ISSN: 1179-7649 (print edition) ISSN: 1179-7657 (online edition) Preview (PDF) PDF
Minelli, A. 2013. Zoological nomenclature in the digital era. Frontiers in zoology 10: 4. DOI: 10.1186/1742-9994-10-4
Nemésio, A. 2011. Nomenclatural itch versus patrolling itch: comments on O’Hara (2011). Zootaxa 2986: 63–68. Preview (PDF)
O’Hara, J.E. 2011. Cyber nomenclaturalists and the “CESA itch”. Zootaxa 2933: 57–64. Preview PDF
Sepkoski, J.J. 2002. A compendium of fossil marine animal genera. Bulletins of American paleontology 363: 1–560. [not seen]
Steyskal, G.C. 1970. On gender concord in binomina. Coleopterists bulletin 24: 57–58. JSTOR
Zhang, Z.-Q. 2012. A new era in zoological nomenclature and taxonomy: ICZN accepts e-publication and launches ZooBank. Zootaxa 3450: 8–8. Preview (PDF). Reference page.

Additional references

Bigatti, G. & Signorelli, J. 2018. Marine invertebrate biodiversity from the Argentine Sea, South Western Atlantic. ZooKeys 791: 47–70. DOI: 10.3897/zookeys.791.22587 Reference page.
Owen, I.L. 2011. Parasites of animals in Papua New Guinea recorded at the National Veterinary Laboratory: a catalogue, historical review and zoogeographical affiliations. Zootaxa 3143: 1–163. Preview (PDF)
Schilthuizen, M. 2013. Something gone awry: unsolved mysteries in the evolution of asymmetric animal genitalia. Animal biology 63: 1–20. DOI: 10.1163/15707563-00002398 Reference page.
Sosa-Medina, T., Vidal-Martínez, V.M. & Aguirre-Macedo, M.L. 2015. Metazoan parasites of fishes from the Celestun coastal lagoon, Yucatan, Mexico. Zootaxa 4007(4): 529–544. DOI: 10.11646/zootaxa.4007.4.4. Preview (PDF). Reference page.
Tasso, V., Haddad, M. el, Assadi, C., Canales, R., Aguirre, L. & Vélez-Zuazo, X. 2018. Macrobenthic fauna from an upwelling coastal area of Peru (Warm Temperate South-eastern Pacific province -Humboldtian ecoregion). Biodiversity Data Journal 6: e28937. DOI: 10.3897/BDJ.6.e28937 Reference page.

BHL bibliography
ZooBank: 0EA9A33B-6B31-4551-B4E2-A772AAF96231

Links

Animalia – Taxon details on Animal Diversity Web (ADW).
Animalia – Taxon details on Catalogue of Life (CoL).
Animalia – Taxon details on Encyclopedia of Life (EOL).
Animalia – Taxon details on EPPO code.
Animalia – Taxon details on Fauna Europaea.
Animalia - Taxon details on Fossiilid.info.

Animalia – Taxon details on Fossilworks.
Animalia – Taxon details on Global Biodiversity Information Facility (GBIF).
Animalia - Taxon details on iNaturalist.

Animalia - Taxon details on Index to Organism Names (ION).

Animalia – Taxon details on Integrated Taxonomic Information System (ITIS).
Animalia – Taxon details on The Linnean Collections.
Animalia – Taxon details on New Zealand Organisms Register (NZOR).
Animalia – Taxon details on Universal Biological Indexer and Organizer (uBio).
Animalia – Taxon details on World Register of Marine Species (WoRMS).

Vernacular names
Afrikaans: Diere
Akan: Mbowa
Alemannisch: Tierer
aragonés: Animals
العربية: حيوانات
asturianu: Animal
অসমীয়া: প্রাণী
Boarisch: Viecher
беларуская: Жывёлы
български: Животни
भोजपुरी: जानवर
bamanankan: Bagan
বাংলা: প্রাণী
brezhoneg: Loen
bosanski: Životinje
català: Animal
Tsetsêhestâhese: Hova
corsu: Animali
Nēhiyawēwin / ᓀᐦᐃᔭᐍᐏᐣ: ᐱᓯᐢᑭᐤ
čeština: Živočichové
Cymraeg: Anifeiliaid
dansk: Dyr
Deutsch: Tiere
Zazaki: Heywani
Ελληνικά: Ζώα
English: Animals
Esperanto: Besto
español: Animales
eesti: Loomad
euskara: Animaliak
فارسی: جانوران
suomi: Eläinkunta
føroyskt: Djór
arpetan: Animâl
Nordfriisk: Diarten
français: Animaux
Frysk: Dier
Gaeilge: Ainmhí
Gàidhlig: Beathach
galego: Animais
עברית: בעלי חיים
हिन्दी: जन्तु; जानवर; जीव; पशु; प्राणी
hrvatski: Životinje
magyar: Állatok
հայերեն: Կենդանիներ
interlingua: Animales
Bahasa Indonesia: Hewan
Ido: Animalo
íslenska: Dýr
italiano: Animali
ᐃᓄᒃᑎᑐᑦ/inuktitut: ᐆᒻᒪᔪᖅ
日本語: 動物界
ქართული: ცხოველები
ភាសាខ្មែរ: សត្វ
ಕನ್ನಡ: ಪ್ರಾಣಿ
한국어: 동물계(動物界)
kurdî: Candar
kernowek: Enyval
Lëtzebuergesch: Déiereräich
Limburgs: Diere
lietuvių: Gyvūnai
latviešu: Dzīvnieki
Malagasy: Biby
македонски: Животни
मराठी: प्राणी
Bahasa Melayu: Haiwan
မြန်မာဘာသာ: တိရစ္ဆာန်
مازِرونی: جانورون
Nāhuatl: Yōlcatl
Plattdüütsch: Beester
Nederlands: Dieren
norsk nynorsk: Dyr
norsk: Dyr
Nouormand: Animâ
occitan: Animals
ଓଡ଼ିଆ: ପ୍ରାଣୀ
Kapampangan: Animal
ਪੰਜਾਬੀ: ਜਾਨਵਰ
polski: zwierzęta
português: Animais
Runa Simi: Uywa
română: Animale
русский: Животные
sicilianu: Armali
srpskohrvatski / српскохрватски: Životinje
Simple English: Animal
slovenčina: Živočíchy
slovenščina: Živali
српски / srpski: Животиња
Sunda: Sato
svenska: Djur
தமிழ்: விலங்கு
ไทย: สัตว์
Tagalog: Hayop
Türkçe: Hayvanlar
українська: Тварини
اردو: جانور
Tiếng Việt: Động vật
West-Vlams: Bêeste
ייִדיש: בעלי־חיים
中文（简体）: 动物界
中文（繁體）: 動物界
粵語: 動物界

Animals (also called Metazoa) are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage in which their body consists of 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 micrometres (0.00033 in) to 33.6 metres (110 ft). They have complex interactions with each other and their environments, forming intricate food webs. The scientific study of animals is known as zoology.

Most living animal species are in Bilateria, a clade whose members have a bilaterally symmetric body plan. The Bilateria include the protostomes, containing invertebrates such as nematodes, arthropods, and molluscs, and the deuterostomes, containing the echinoderms and the chordates, the latter 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.

Historically, 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 for 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 taxa.

Humans make use of many animal species, such as for food (including meat, milk, and eggs), for materials (such as leather and wool), as pets, and as working animals including for transport. Dogs have been used in hunting, as have birds of prey, while many terrestrial and aquatic animals were hunted for sports. Nonhuman animals have appeared in art from the earliest times and are featured in mythology and religion.

Etymology

The word animal comes from the Latin animalis, meaning 'having breath', 'having soul' or 'living being'.[1] The biological definition includes all members of the kingdom Animalia.[2] In colloquial usage, the term animal is often used to refer only to nonhuman animals.[3][4][5][6]
Characteristics
Animals are unique in having the ball of cells of the early embryo (1) develop into a hollow ball or blastula (2).

Animals have several characteristics that set them apart from other living things. Animals are eukaryotic and multicellular.[7][8] Unlike plants and algae, which produce their own nutrients,[9] animals are heterotrophic,[8][10] feeding on organic material and digesting it internally.[11] With very few exceptions, (example; Henneguya zschokkei[12]) animals respire aerobically.[13] All animals are motile[14] (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 animals,[15] (though it has been lost in some) 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.[16] 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.[17] 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.[18] Animal cells uniquely possess the cell junctions called tight junctions, gap junctions, and desmosomes.[19]

With few exceptions—in particular, the sponges and placozoans—animal bodies are differentiated into tissues.[20] 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).[21]
Reproduction and development
Sexual reproduction is nearly universal in animals, such as these dragonflies.
See also: Sexual reproduction § Animals, and Asexual reproduction § Examples in animals

Nearly all animals make use of some form of sexual reproduction.[22] They produce haploid gametes by meiosis; the smaller, motile gametes are spermatozoa and the larger, non-motile gametes are ova.[23] These fuse to form zygotes,[24] 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.[25] In most other groups, the blastula undergoes more complicated rearrangement.[26] It first invaginates to form a gastrula with a digestive chamber and two separate germ layers, an external ectoderm and an internal endoderm.[27] In most cases, a third germ layer, the mesoderm, also develops between them.[28] These germ layers then differentiate to form tissues and organs.[29]

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.[30][31] Animals have evolved numerous mechanisms for avoiding close inbreeding.[32]

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.[33][34]
Ecology
Predators, such as this ultramarine flycatcher (Ficedula superciliaris), feed on other animals.

Animals are categorised into ecological groups depending on how they obtain or consume organic material, including carnivores, herbivores, omnivores, detritivores,[35] and parasites.[36] 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).[37] Selective pressures imposed on one another lead to an evolutionary arms race between predator and prey, resulting in various anti-predator adaptations.[38][39] Almost all multicellular predators are animals.[40] Some consumers use multiple methods; for example, in parasitoid wasps, the larvae feed on the hosts' living tissues, killing them in the process,[41] but the adults primarily consume nectar from flowers.[42] Other animals may have very specific feeding behaviours, such as hawksbill sea turtles primarily eating sponges.[43]
Hydrothermal vent mussels and shrimps

Most animals rely on the biomass and energy produced by plants through photosynthesis. Herbivores eat plant material directly, while carnivores, and other animals on higher trophic levels typically acquire it indirectly by eating other animals. Animals oxidize carbohydrates, lipids, proteins, and other biomolecules to unlock the chemical energy of molecular oxygen,[44] which allows the animal to grow and to sustain biological processes such as locomotion.[45][46][47] Animals living close to hydrothermal vents and cold seeps on the dark sea floor consume organic matter of archaea and bacteria produced in these locations through chemosynthesis (by oxidizing inorganic compounds, such as hydrogen sulfide).[48]

Animals originally evolved in the sea. Lineages of arthropods colonised land around the same time as land plants, probably between 510 and 471 million years ago during the Late Cambrian or Early Ordovician.[49] Vertebrates such as the lobe-finned fish Tiktaalik started to move on to land in the late Devonian, about 375 million years ago.[50][51] 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.[52] Animals are however not particularly heat tolerant; very few of them can survive at constant temperatures above 50 °C (122 °F).[53] Only very few species of animals (mostly nematodes) inhabit the most extreme cold deserts of continental Antarctica.[54]
Diversity
The blue whale is the largest animal that has ever lived.
Size
Further information: Largest organisms and Smallest organisms

The blue whale (Balaenoptera musculus) is the largest animal that has ever lived, weighing up to 190 tonnes and measuring up to 33.6 metres (110 ft) long.[55][56][57] The largest extant terrestrial animal is the African bush elephant (Loxodonta africana), weighing up to 12.25 tonnes[55] and measuring up to 10.67 metres (35.0 ft) long.[55] The largest terrestrial animals that ever lived were titanosaur sauropod dinosaurs such as Argentinosaurus, which may have weighed as much as 73 tonnes.[58] Several animals are microscopic; some Myxozoa (obligate parasites within the Cnidaria) never grow larger than 20 µm,[59] and one of the smallest species (Myxobolus shekel) is no more than 8.5 µm when fully grown.[60]
Numbers and habitats

The following table lists estimated numbers of described extant species for the animal groups with the largest numbers of species,[61] along with their principal habitats (terrestrial, fresh water,[62] and marine),[63] and free-living or parasitic ways of life.[64] 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.[65] 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.[66][67][a]

Evolutionary origin
Further information: Urmetazoan
Dickinsonia costata from the Ediacaran biota (c. 635–542 MYA) is one of the earliest animal species known.[79]

The 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.[80]

Animals are found as long ago as the Ediacaran biota, towards the end of the Precambrian, and possibly somewhat earlier. It had long been doubted whether these life-forms included animals,[81][82][83] but the discovery of the animal lipid cholesterol in fossils of Dickinsonia establishes their nature.[79] 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.[84]
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 shale.

Many 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.[85][86][87][88]

Some palaeontologists have suggested that animals appeared much earlier than the Cambrian explosion, possibly as early as 1 billion years ago.[89] 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.[90] 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.[91][92] Around the same time, the layered mats of microorganisms called stromatolites decreased in diversity, perhaps due to grazing by newly evolved animals.[93]
Phylogeny
Further information: 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.[94] 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,[95] both of which lack hox genes, important in body plan development.[96]

These genes are found in the Placozoa[97][98] and the higher animals, the Bilateria.[99][100] 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.[101][102]

The phylogenetic tree (of major lineages only) indicates approximately how many millions of years ago (mya) the lineages split.[103][104][105][106][107]

Non-bilateria
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.[108] Sponges lack the complex organization found in most other animal phyla;[109] their cells are differentiated, but in most cases not organised into distinct tissues.[110] They typically feed by drawing in water through pores.[111]

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.[112] Animals in both phyla have distinct tissues, but these are not organised into organs.[113] They are diploblastic, having only two main germ layers, ectoderm and endoderm.[114] The tiny placozoans are similar, but they do not have a permanent digestive chamber.[115][116]
Bilateria
Main articles: Bilateria and Symmetry (biology) § Bilateral symmetry
Idealised bilaterian body plan.[c] 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.[117][118]

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;[118] these enable soft-bodied animals with a hydrostatic skeleton to move by peristalsis.[119] 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.[117][118]

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.[120] The basalmost bilaterians are the Xenacoelomorpha.[121][122][123]
Protostomes and deuterostomes
Further information: Embryological origins of the mouth and anus
The bilaterian gut develops in two ways. In many protostomes, the blastopore develops into the mouth, while in deuterostomes it becomes the anus.
Main articles: Protostome and Deuterostome

Protostomes 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.[124] 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.[125][126] 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.[127]

The main deuterostome phyla are the Echinodermata and the Chordata.[128] Echinoderms are exclusively marine and include starfish, sea urchins, and sea cucumbers.[129] The chordates are dominated by the vertebrates (animals with backbones),[130] which consist of fishes, amphibians, reptiles, birds, and mammals.[131] The deuterostomes also include the Hemichordata (acorn worms).[132][133]
Ecdysozoa
Ecdysis: a dragonfly has emerged from its dry exuviae and is expanding its wings. Like other arthropods, its body is divided into segments.
Main article: Ecdysozoa

The Ecdysozoa are protostomes, named after their shared trait of ecdysis, growth by moulting.[134] 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;[135] some are important parasites.[136] 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.[137]
Spiralia
Main article: Spiralia
Spiral cleavage in a sea snail embryo

The Spiralia are a large group of protostomes that develop by spiral cleavage in the early embryo.[138] 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.[139][140]

The Lophotrochozoa includes the molluscs, annelids, brachiopods, nemerteans, bryozoa and entoprocts.[139][141][142] 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.[143][144]
History of classification
Further information: Taxonomy (biology), History of zoology (through 1859), and History of zoology since 1859
Jean-Baptiste de Lamarck led the creation of a modern classification of invertebrates, breaking up Linnaeus's "Vermes" into 9 phyla by 1809.[145]

In the classical era, Aristotle divided animals,[d] 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.[146]

In 1758, Carl Linnaeus created the first hierarchical classification in his Systema Naturae.[147] 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)[e] 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.[145]

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).[149] 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.[150]

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.[151][150] The protozoa were later moved to the former kingdom Protista, leaving only the Metazoa as a synonym of Animalia.[152]
In human culture
Practical uses
Sides of beef in a slaughterhouse
Main article: Animals in culture

The 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.[153][154] Marine fish of many species are caught commercially for food. A smaller number of species are farmed commercially.[153][155][156] Humans and their livestock make up more than 90% of the biomass of all terrestrial vertebrates, and almost as much as all insects combined.[157]

Invertebrates including cephalopods, crustaceans, and bivalve or gastropod molluscs are hunted or farmed for food.[158] Chickens, cattle, sheep, pigs, and other animals are raised as livestock for meat across the world.[154][159][160] 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.[161] Dyestuffs including carmine (cochineal),[162][163] shellac,[164][165] and kermes[166][167] 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.[168]

Animals such as the fruit fly Drosophila melanogaster serve a major role in science as experimental models.[169][170][171][172] Animals have been used to create vaccines since their discovery in the 18th century.[173] Some medicines such as the cancer drug Yondelis are based on toxins or other molecules of animal origin.[174]
A gun dog retrieving a duck during a hunt

People have used hunting dogs to help chase down and retrieve animals,[175] and birds of prey to catch birds and mammals,[176] while tethered cormorants have been used to catch fish.[177] Poison dart frogs have been used to poison the tips of blowpipe darts.[178][179] A wide variety of animals are kept as pets, from invertebrates such as tarantulas and octopuses, insects including praying mantises,[180] reptiles such as snakes and chameleons,[181] and birds including canaries, parakeets, and parrots[182] all finding a place. However, the most kept pet species are mammals, namely dogs, cats, and rabbits.[183][184][185] There is a tension between the role of animals as companions to humans, and their existence as individuals with rights of their own.[186] A wide variety of terrestrial and aquatic animals are hunted for sport.[187]
Symbolic uses
Artistic vision: Still Life with Lobster and Oysters by Alexander Coosemans, c. 1660

Animals 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.[188] Insects, birds and mammals play roles in literature and film,[189] such as in giant bug movies.[190][191][192]

Animals including insects[193] and mammals[194] feature in mythology and religion. In both Japan and Europe, a butterfly was seen as the personification of a person's soul,[193][195][196] while the scarab beetle was sacred in ancient Egypt.[197] Among the mammals, cattle,[198] deer,[194] horses,[199] lions,[200] bats,[201] bears,[202] and wolves[203] are the subjects of myths and worship. The signs of the Western and Chinese zodiacs are based on animals.[204][205]
See also

Animal attacks
Animal coloration
Ethology
Fauna
List of animal names
Lists of organisms by population

Notes

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).[68]
Not including parasitoids.[64]
Compare File:Annelid redone w white background.svg for a more specific and detailed model of a particular phylum with this general body plan.
In his History of Animals and Parts of Animals.

The prefix une espèce de is pejorative.[148]

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