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 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. ( Full article...)

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 ('animal'), and λόγος, logos ('knowledge', 'study'). ( Full article...)

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The platypus (Ornithorhynchus anatinus), sometimes referred to as the duck-billed platypus, is a semiaquatic, egg-laying mammal endemic to eastern Australia, including Tasmania. The platypus is the sole living representative of its family ( Ornithorhynchidae) and genus (Ornithorhynchus), though a number of related species appear in the fossil record.

Together with the four species of echidna, it is one of the five extant species of monotremes, the only mammals that lay eggs instead of giving birth to live young; they are all native to Australia. Like other monotremes, it senses prey through electrolocation. It is one of the few species of venomous mammals, as the male platypus has a spur on the hind foot that delivers a venom, capable of causing severe pain to humans. The unusual appearance of this egg-laying, duck-billed, beaver-tailed, otter-footed mammal baffled European naturalists when they first encountered it, and the first scientists to examine a preserved platypus body (in 1799) judged it a fake, made of several animals sewn together. ( Full article...)
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Anti-predator adaptation in action: the seal shark Dalatias licha (a–c) and the wreckfish Polyprion americanus (d–f) attempt to prey on hagfishes. First, the predators approach their potential prey. Predators bite or try to swallow the hagfishes, but the hagfishes have already projected jets of slime (arrows) into the predators' mouths. Choking, the predators release the hagfishes and gag in an attempt to remove slime from their mouths and gill chambers.

Anti-predator adaptations are mechanisms developed through evolution that assist prey organisms in their constant struggle against predators. Throughout the animal kingdom, adaptations have evolved for every stage of this struggle, namely by avoiding detection, warding off attack, fighting back, or escaping when caught.

The first line of defence consists in avoiding detection, through mechanisms such as camouflage, masquerade, apostatic selection, living underground, or nocturnality. ( Full article...)
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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.