Portal:Animals

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Animals (also called Metazoa) 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 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 kingdom Animalia includes humans but in colloquial use the term animal often refers only to non-human animals. 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—in which many groups of invertebrates are found, such as nematodes, arthropods, and molluscs—and the deuterostomes, containing both the echinoderms as well as the chordates, the latter containing 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.

Zoology (/zˈɒləi/) is the branch of biology that studies the animal kingdom, including the structure, embryology, evolution, classification, habits, and distribution of all animals, both living and extinct, and how they interact with their ecosystems. The term is derived from Ancient Greek ζῷον, zōion, i.e. "animal" and λόγος, logos, i.e. "knowledge, study".

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Starfish or sea stars are star-shaped echinoderms belonging to the class Asteroidea. Common usage frequently finds these names being also applied to ophiuroids, which are correctly referred to as brittle stars or basket stars. Starfish are also known as Asteroids due to being in the class Asteroidea. About 1,500 species of starfish occur on the seabed in all the world's oceans, from the tropics to frigid polar waters. They are found from the intertidal zone down to abyssal depths, 6,000 m (20,000 ft) below the surface.

Starfish are marine invertebrates. They typically have a central disc and usually five arms, though some species have a larger number of arms. The aboral or upper surface may be smooth, granular or spiny, and is covered with overlapping plates. Many species are brightly coloured in various shades of red or orange, while others are blue, grey or brown. Starfish have tube feet operated by a hydraulic system and a mouth at the centre of the oral or lower surface. They are opportunistic feeders and are mostly predators on benthic invertebrates. Several species have specialized feeding behaviours including eversion of their stomachs and suspension feeding. They have complex life cycles and can reproduce both sexually and asexually. Most can regenerate damaged parts or lost arms and they can shed arms as a means of defense. The Asteroidea occupy several significant ecological roles. Starfish, such as the ochre sea star (Pisaster ochraceus) and the reef sea star (Stichaster australis), have become widely known as examples of the keystone species concept in ecology. The tropical crown-of-thorns starfish (Acanthaster planci) is a voracious predator of coral throughout the Indo-Pacific region, and the northern Pacific sea star is considered to be one of the world's 100 worst invasive species. Read more...

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Bornean orangutan
(Pongo pygmaeus)

Orangutans (genus Pongo, also spelled orang-utan, orangutang, or orang-utang) are great apes native to Indonesia and Malaysia. They are found in the rainforests of Borneo and Sumatra, but during the Pleistocene they ranged throughout Southeast Asia and South China. Classified in the genus Pongo, orangutans were originally considered to be one species. From 1996, they were divided into two species: the Bornean orangutan (P. pygmaeus, with three subspecies) and the Sumatran orangutan (P. abelii). In 2017, a third species, the Tapanuli orangutan (P. tapanuliensis), was identified. The orangutans are the only surviving species of the subfamily Ponginae, who split from humans, chimpanzees and gorillas 19.3 to 15.7 million years ago (mya).

The most arboreal of the great apes, orangutans spend most of their time in trees. They have proportionally long arms and short legs and their hair is reddish-brown. Adult males may develop distinctive cheek pads or flanges and make long calls that attract females and intimidate rivals; younger males do not and resemble adult females. Orangutans are the most solitary of the great apes, social bonds occurring primarily between mothers and their dependent offspring, who remain together for the first two years. Fruit is the most important component of an orangutan's diet, but the apes will also eat vegetation, bark, honey, insects and bird eggs. They can live over 30 years both in the wild and in captivity. Read more...
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Coral
Credit: Toby Hudson

Corals are marine invertebrates that typically live in compact colonies of many identical individual polyps. Each polyp is a sac-like animal typically only a few millimeters in diameter and a few centimeters in length. Corals are major contributors to the physical structure of the coral reefs such as the Great Barrier Reef, where this photograph was taken. Coral reefs are under threat globally from ocean acidification and climate change.

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The following table lists estimated numbers of described extant species for the animal groups with the largest numbers of species,[1] along with their principal habitats (terrestrial, fresh water,[2] and marine),[3] and free-living or parasitic ways of life.[4] 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.[5] 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.[6][7][a]

Phylum Example No. of
Species
Land Sea Fresh
water
Free-
living
Parasitic
Annelids Nerr0328.jpg 17,000[1] Yes (soil)[3] Yes[3] 1,750[2] Yes 400[4]
Arthropods wasp 1,257,000[1] 1,000,000
(insects)[9]
>40,000
(Malac-
ostraca)[10]
94,000[2] Yes[3] >45,000[b][4]
Bryozoa Bryozoan at Ponta do Ouro, Mozambique (6654415783).jpg 6,000[1] Yes[3] 60–80[2] Yes
Chordates green spotted frog facing right 65,000[1]
45,000[11]

23,000[11]

13,000[11]
18,000[2]
9,000[11]
Yes 40
(catfish)[12][4]
Cnidaria Table coral 16,000[1] Yes[3] Yes (few)[3] Yes[3] >1,350
(Myxozoa)[4]
Echinoderms Starfish, Caswell Bay - geograph.org.uk - 409413.jpg 7,500[1] 7,500[1] Yes[3]
Molluscs snail 85,000[1]
107,000[13]

35,000[13]

60,000[13]
5,000[2]
12,000[13]
Yes[3] >5,600[4]
Nematodes CelegansGoldsteinLabUNC.jpg 25,000[1] Yes (soil)[3] 4,000[5] 2,000[2] 11,000[5] 14,000[5]
Platyhelminthes Pseudoceros dimidiatus.jpg 29,500[1] Yes[14] Yes[3] 1,300[2] Yes[3]

3,000–6,500[15]

>40,000[4]

4,000–25,000[15]

Rotifers 20090730 020239 Rotifer.jpg 2,000[1] >400[16] 2,000[2] Yes
Sponges A colourful Sponge on the Fathom.jpg 10,800[1] Yes[3] 200-300[2] Yes Yes[17]
Total number of described extant species as of 2013: 1,525,728[1]

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  1. ^ 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).[8]
  2. ^ Not including parasitoids.[4]
  1. ^ a b c d e f g h i j k l m n Zhang, Zhi-Qiang (2013-08-30). "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): 5. doi:10.11646/zootaxa.3703.1.3. Archived from the original on 24 April 2019. Retrieved 2 March 2018.
  2. ^ a b c d e f g h i j Balian, E. V.; Lévêque, C.; Segers, H.; Martens, K. (2008). Freshwater Animal Diversity Assessment. Springer. p. 628. ISBN 978-1-4020-8259-7.
  3. ^ a b c d e f g h i j k l m n Hogenboom, Melissa. "There are only 35 kinds of animal and most are really weird". BBC Earth. Archived from the original on 10 August 2018. Retrieved 2 March 2018.
  4. ^ a b c d e f g h Poulin, Robert (2007). Evolutionary Ecology of Parasites. Princeton University Press. p. 6. ISBN 978-0-691-12085-0.
  5. ^ a b c d Felder, Darryl L.; Camp, David K. (2009). Gulf of Mexico Origin, Waters, and Biota: Biodiversity. Texas A&M University Press. p. 1111. ISBN 978-1-60344-269-5.
  6. ^ "How many species on Earth? About 8.7 million, new estimate says". 24 August 2011. Archived from the original on 1 July 2018. Retrieved 2 March 2018.
  7. ^ Mora, Camilo; Tittensor, Derek P.; Adl, Sina; Simpson, Alastair G.B.; Worm, Boris (2011-08-23). Mace, Georgina M. (ed.). "How Many Species Are There on Earth and in the Ocean?". PLOS Biology. 9 (8): e1001127. doi:10.1371/journal.pbio.1001127. PMC 3160336. PMID 21886479.
  8. ^ 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. (1 August 2016). "Counting animal species with DNA barcodes: Canadian insects". Philosophical Transactions of the Royal Society B: Biological Sciences. 371 (1702): 20150333. doi:10.1098/rstb.2015.0333. PMC 4971185. PMID 27481785.
  9. ^ Stork, Nigel E. (January 2018). "How Many Species of Insects and Other Terrestrial Arthropods Are There on Earth?". Annual Review of Entomology. 63 (1): 31–45. doi:10.1146/annurev-ento-020117-043348. PMID 28938083. S2CID 23755007. Stork notes that 1m insects have been named, making much larger predicted estimates.
  10. ^ Poore, Hugh F. (2002). "Introduction". Crustacea: Malacostraca. Zoological catalogue of Australia. 19.2A. CSIRO Publishing. pp. 1–7. ISBN 978-0-643-06901-5.
  11. ^ a b c d Reaka-Kudla, Marjorie L.; Wilson, Don E.; Wilson, Edward O. (1996). Biodiversity II: Understanding and Protecting Our Biological Resources. Joseph Henry Press. p. 90. ISBN 978-0-309-52075-1.
  12. ^ Burton, Derek; Burton, Margaret (2017). Essential Fish Biology: Diversity, Structure and Function. Oxford University Press. pp. 281–282. ISBN 978-0-19-878555-2. 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.
  13. ^ a b c d Nicol, David (June 1969). "The Number of Living Species of Molluscs". Systematic Zoology. 18 (2): 251–254. doi:10.2307/2412618. JSTOR 2412618.
  14. ^ Sluys, R. (1999). "Global diversity of land planarians (Platyhelminthes, Tricladida, Terricola): a new indicator-taxon in biodiversity and conservation studies". Biodiversity and Conservation. 8 (12): 1663–1681. doi:10.1023/A:1008994925673. S2CID 38784755.
  15. ^ a b Pandian, T. J. (2020). Reproduction and Development in Platyhelminthes. CRC Press. pp. 13–14. ISBN 9781000054903.
  16. ^ Fontaneto, Diego. "Marine Rotifers | An Unexplored World of Richness" (PDF). JMBA Global Marine Environment. pp. 4–5. Archived (PDF) from the original on 2 March 2018. Retrieved 2 March 2018.
  17. ^ Morand, Serge; Krasnov, Boris R.; Littlewood, D. Timothy J. (2015). Parasite Diversity and Diversification. Cambridge University Press. p. 44. ISBN 978-1-107-03765-6. Archived from the original on 12 December 2018. Retrieved 2 March 2018.