Animals are multicellular, eukaryotic organisms belonging to the biological kingdom Animalia (). With few exceptions, animals consume organic material, breathe oxygen, have myocytes and are able to move, can reproduce sexually, and grow from a hollow sphere of cells, the blastula, during embryonic development. Animals form a clade, meaning that they arose from a single common ancestor. Over 1.5 million living animal species have been described, of which around 1.05 million are insects, over 85,000 are molluscs, and around 65,000 are vertebrates. It has been estimated there are as many as 7.77 million animal species on Earth. Animal body lengths range from 8.5 μm (0.00033 in) to 33.6 m (110 ft). They have complex ecologies and interactions with each other and their environments, forming intricate food webs. The scientific study of animals is known as zoology, and the study of animal behaviour is known as ethology.
The animal kingdom is divided into five major clades, namely Porifera, Ctenophora, Placozoa, Cnidaria and Bilateria. Most living animal species belong to the clade Bilateria, a highly proliferative clade whose members have a bilaterally symmetric and significantly cephalised body plan, and the vast majority of bilaterians belong to two large clades: the protostomes, which includes organisms such as arthropods, molluscs, flatworms, annelids and nematodes; and the deuterostomes, which include echinoderms, hemichordates and chordates, the latter of which contains the vertebrates. The much smaller basal phylum Xenacoelomorpha have an uncertain position within Bilateria.
Animals first appeared in the fossil record in the late Cryogenian period and diversified in the subsequent Ediacaran period in what is known as the Avalon explosion. Nearly all modern animal phyla first appeared in the fossil record as marine species during the Cambrian explosion, which began around 539 million years ago (Mya), and most classes during the Ordovician radiation 485.4 Mya. Common to all living animals, 6,331 groups of genes have been identified that may have arisen from a single common ancestor that lived about 650 Mya during the Cryogenian period. (Full article...)
Zoology ( zoh-OL-ə-jee, zoo-) is the scientific study of animals. Its studies include the structure, embryology, classification, habits, and distribution of all animals, both living and extinct, and how they interact with their ecosystems. Zoology is one of the primary branches of biology. The term is derived from Ancient Greek ζῷον (zôion) 'animal' and λόγος (lógos) 'study of'. (Full article...)
Entries here consist of Good and Featured articles, which meet a core set of high editorial standards.
The bluebuck (Afrikaans: bloubok ) or blue antelope (Hippotragus leucophaeus) is an extinct species of antelope that lived in South Africa until around 1800. It was smaller than the other two species in its genus Hippotragus, the roan antelope and sable antelope. The bluebuck was sometimes considered a subspecies of the roan antelope, but a genetic study has confirmed it as a distinct species.
The largest mounted bluebuck specimen is 119 centimetres (47 in) tall at the withers. Its horns measure 56.5 centimetres (22.2 in) along the curve. The coat was a uniform bluish-grey, with a pale whitish belly. The forehead was brown, darker than the face. Its mane was not as developed as in the roan and sable antelopes; its ears were shorter and blunter, not tipped with black; and it had a darker tail tuft and smaller teeth. It also lacked the contrasting black and white patterns seen on the heads of its relatives. The bluebuck was a grazer, and may have calved where rainfall, and thus the availability of grasses, would peak. The bluebuck was confined to the southwestern Cape when encountered by Europeans, but fossil evidence and rock paintings show that it originally had a larger distribution. (Full article...)
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Image 1Photograph: Hans Hillewaert The common clam worm ( Alitta succinea) is a widely distributed species of marine polychaete worm. The photograph shows an epitoke specimen, the worm having turned into a form capable of reproduction. After releasing its sperm or eggs, the animal will die.
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Image 2Photograph credit: Frank Schulenburg The brown pelican ( Pelecanus occidentalis) is a bird of the pelican family, Pelecanidae, one of three species found in the Americas and one of two that feed by diving into water. This photograph shows a juvenile brown pelican gliding over the Pacific Ocean at Bodega Head, California. After hatching, the pelican chicks are fed on regurgitated predigested fish and take about two months to fledge. When they leave the nest, they are at first unable to fly and take wing several weeks later. When the parents cease to feed them, some six months later, each will have consumed around 70 kg (150 lb) of fish. The juvenile brown pelican does not acquire adult plumage until three years of age, when the feathers on the neck become paler, the upperparts striped, the wing feathers grayer, and the belly acquires dark spots.
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Image 3Photograph credit: Paolo Costa Baldi Sexual dimorphism is the condition where the two sexes of the same species exhibit different characteristics. Differences may include secondary sex characteristics, size, weight, color, or markings, as well as behavioral and cognitive differences. In the butterfly species Colias dimera (also known as the Dimera sulphur), seen here mating in Venezuela, the male on the right is a brighter shade of yellow than the female.
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Image 4The Osprey ( Pandion haliaetus) is a medium large raptor which is a specialist fish-eater with a worldwide distribution. It is often known by other colloquial names such as Fish Hawk, Sea Hawk or Fish Eagle. The Osprey is particularly well adapted to its diet, with reversible outer toes, closable nostrils to keep out water during dives, and backwards facing scales on the talons which act as barbs to help catch fish.
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Image 5Photograph: Gabriel Barathieu
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Image 6Photograph: Kateshortforbob
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Image 9Photograph credit: Charles J. Sharp The bird-cherry ermine ( Yponomeuta evonymella) is a species of moth in the family Yponomeutidae, native to Europe and parts of Asia. The caterpillars are gregarious and feed on the leaves of the bird cherry tree, forming silken webbing for their own protection. They create further webbing on the trunk and near the base of the tree, which hides them as they pupate. This photograph shows one of many bird-cherry ermine caterpillar nests on a tree in Lahemaa National Park, Estonia. In some years, they are so numerous that they can completely strip a tree of its foliage.
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Image 10Photograph credit: Basile Morin Eutropis macularia, the bronze grass skink, is a species of lizard in the skink family, Scincidae, native to South and Southeast Asia. It lives in both deciduous and evergreen forests, in plantations, in grasslands, and in rocky areas with scattered trees. The species is active in both the day and the night, feeding on insects and other invertebrates. This bronze grass skink was photographed on a tree trunk on the island of Don Det in Laos.
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Image 11A female Calliope Hummingbird ( Stellula calliope), the smallest bird found in Canada and the United States, feeding insects to chicks. Found mostly in western North America (although vagrants have been found in New York and Connecticut), it is migratory and winters in southwestern Mexico.
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Image 12Bryozoa (also known as the Polyzoa, Ectoprocta or commonly as moss animals) are a phylum of simple, aquatic invertebrate animals, nearly all living in sedentary colonies. Typically about 0.5 millimetres ( 1⁄64 in) long, they have a special feeding structure called a lophophore, a "crown" of tentacles used for filter feeding. The bryozoans are classified as the marine bryozoans (Stenolaemata), freshwater bryozoans (Phylactolaemata), and mostly-marine bryozoans (Gymnolaemata), a few members of which prefer brackish water. Most marine bryozoans live in tropical waters, but a few are found in oceanic trenches and polar waters. 5,869 living species of bryozoa are known. Originally all of the crown group Bryozoa were colonial, but as an adaptation to a mesopsammal (interstitial spaces in marine sand) life or to deep-sea habitats, secondarily solitary forms have since evolved. Solitary species have been described in four genera: Aethozooides, Aethozoon, Franzenella, and Monobryozoon, the latter having a statocyst-like organ with a supposed excretory function. ( Full article...)
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Image 13Brittle stars, serpent stars, or ophiuroids (from Latin ophiurus 'brittle star'; from Ancient Greek ὄφις (óphis) 'serpent' and οὐρά (ourá) 'tail'; referring to the serpent-like arms of the brittle star) are echinoderms in the class Ophiuroidea, closely related to starfish. They crawl across the sea floor using their flexible arms for locomotion. The ophiuroids generally have five long, slender, whip-like arms which may reach up to 60 cm (24 in) in length on the largest specimens. ( Full article...)
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Image 14Photograph: Didier Descouens A caterpillar of Lymantria dispar dispar, also known as the gypsy moth. First described by Carl Linnaeus in 1758, the gypsy moth is found throughout Eurasia, where it is considered a pest. The larvae emerge from egg masses in the spring, and then are dispersed by the wind and begin feeding on leaves. They are initially diurnal, but become nocturnal after their fourth molting.
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Image 17Credit: Twilight Zone Expedition Team 2007, NOAA-OE
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Image 18Plate 5 from Ernst Haeckel's Kunstformen der Natur, showing a variety of calcareous sponges, a class of about 400 marine sponges that are found mostly in shallow tropical waters worldwide. Calcareous sponges vary from radially symmetrical vase-shaped body types to colonies made up of a meshwork of thin tubes, or irregular massive forms. The skeleton has either a mesh or honeycomb structure.
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Image 19Photograph: Taro Taylor; edit: Dapete Glaucus atlanticus is a species of small, blue sea slug. This pelagic aeolid nudibranch floats upside down, using the surface tension of the water to stay up, and is carried along by the winds and ocean currents. The blue side of their body faces upwards, blending in with the blue of the water, while the grey side faces downwards, blending in with the silvery surface of the sea. G. atlanticus feeds on other pelagic creatures, including the Portuguese man o' war.
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Selected article - Entries here consist of Good and Featured articles, which meet a core set of high editorial standards.
Animal Coloration, or in full Animal Coloration: An Account of the Principal Facts and Theories Relating to the Colours and Markings of Animals, is a book by the English zoologist Frank Evers Beddard, published by Swan Sonnenschein in 1892. It formed part of the ongoing debate amongst zoologists about the relevance of Charles Darwin's theory of natural selection to the observed appearance, structure, and behaviour of animals, and vice versa.
Beddard states in the book that it contains little that is new, intending instead to give a clear overview of the subject. The main topics covered are camouflage, then called 'protective coloration'; mimicry; and sexual selection. Arguments for and against these aspects of animal coloration are intensively discussed in the book. (Full article...)
- ...that six new species of marine slugs in the genus Phyllodesmium (Sp. kabiranum pictured) have been described in the last two years?
- ...that Maui's dolphin is the most endangered species of dolphin in the world, with only about 110 left?
- ...that the land snail Euglandina rosea is a significant threat to Hawaiian freshwater snail known as Newcomb's snail (Erinna newcombi), because the predatory Euglandina is able to hunt Erinna under water?
- ...that the body of the "X-ray fish" (Pristella maxillaris ) is so transparent that it is possible to see its backbone?
- ...that even though the lancelets are classified as chordates, they lack a true backbone and well-defined head?
The following are images from various animal-related articles on Wikipedia.
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Image 1Butterfly wing at different magnifications reveals microstructured chitin acting as diffraction grating. (from Animal coloration)
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Image 2Myxozoans such as Myxobolus cerebralis are single-celled parasites, never more than 20 μm across. (from Animal)
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Image 4The bilaterian gut develops in two ways. In many protostomes, the blastopore develops into the mouth, while in deuterostomes it becomes the anus. (from Animal)
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Image 5Sides of beef in a slaughterhouse (from Animal)
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Image 6This frog changes its skin colour to control its temperature. (from Animal coloration)
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Image 7Bright coloration of orange elephant ear sponge, Agelas clathrodes signals its bitter taste to predators (from Animal coloration)
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Image 8In Roseate Spoonbills 1905–1909, Abbott Handerson Thayer tried to show that even the bright pink of these conspicuous birds had a cryptic function. (from Animal coloration)
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Image 9The blue whale is the largest animal that has ever lived; it can be up to 33.6 metres (110 ft) long. (from Animal)
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Image 10Examples of fauna in Olleros de Tera ( Spain) (from Fauna)
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Image 11The black and yellow warning colours of the cinnabar moth caterpillar, Tyria jacobaeae, are avoided by some birds. (from Animal coloration)
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Image 12Kelp gull chicks peck at red spot on mother's beak to stimulate the regurgitating reflex. (from Zoology)
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Image 13Non-bilaterians include sponges (centre) and corals (background). (from Animal)
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Image 14The olm's blood makes it appear pink. (from Animal coloration)
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Image 15A venomous coral snake uses bright colours to warn off potential predators. (from Animal coloration)
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Image 16The microscopic cave snail Zospeum tholussum, found at depths of 743 to 1,392 m (2,438 to 4,567 ft) in the Lukina Jama–Trojama cave system of Croatia, is completely blind with a translucent shell (from Fauna)
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Image 17Linnaeus's table of the animal kingdom from the first edition of Systema Naturae (1735) (from Zoology)
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Image 18Fish and frog melanophores are cells that can change colour by dispersing or aggregating pigment-containing bodies. (from Animal coloration)
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Image 19A gun dog retrieving a duck during a hunt (from Animal)
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Image 20The brilliant iridescent colours of the peacock's tail feathers are created by Structural coloration. (from Animal coloration)
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Image 22Papuan, Australian and New Zealand fauna. This image was likely first published in the first edition (1876–1899) of the Nordisk familjebok. (from Fauna)
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Image 23The red pigment in a flamingo's plumage comes from its diet of shrimps, which get it from microscopic algae. (from Animal coloration)
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Image 25Animals are unique in having the ball of cells of the early embryo (1) develop into a hollow ball or blastula (2). (from Animal)
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Image 26Idealised nephrozoan 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. (from Animal)
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Image 28Predators, such as this ultramarine flycatcher ( Ficedula superciliaris), feed on other animals. (from Animal)
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Image 29Sexual reproduction is nearly universal in animals, such as these dragonflies. (from Animal)
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Image 30The hawk-cuckoo resembles a predatory shikra, giving the cuckoo time to lay eggs in a songbird's nest unnoticed (from Animal coloration)
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Image 31A clade representation of seven dog breeds in relation to wolves. (from Zoology)
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Image 32A praying mantis in deimatic or threat pose displays conspicuous patches of colour to startle potential predators. This is not warning coloration as the insect is palatable. (from Animal coloration)
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Image 33Hydrothermal vent mussels and shrimps (from Animal)
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Image 34Artistic vision: Still Life with Lobster and Oysters by Alexander Coosemans, c. 1660 (from Animal)
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Image 35A camouflaged orange oak leaf butterfly, Kallima inachus (centre) has protective resemblance. (from Animal coloration)
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Image 36Side of zebrafish shows how chromatophores (dark spots) respond to 24 hours in dark (above) or light (below). (from Animal coloration)
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Image 37Squid chromatophores appear as black, brown, reddish and pink areas in this micrograph. (from Animal coloration)
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Image 38Male Goldie's bird-of-paradise displays to a female. (from Animal coloration)
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Image 39The Spiralia develop with spiral cleavage in the embryo, as here in a sea snail. (from Animal)
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Image 40Warning coloration of the skunk in Edward Bagnall Poulton's The Colours of Animals, 1890 (from Animal coloration)
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Image 41Robert Hooke's Micrographia (from Animal coloration)
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Image 42Jean-Baptiste de Lamarck led the creation of a modern classification of invertebrates, breaking up Linnaeus's "Vermes" into nine phyla by 1809. (from Animal)
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Image 43A brilliantly-coloured oriental sweetlips fish ( Plectorhinchus vittatus) waits while two boldly-patterned cleaner wrasse ( Labroides dimidiatus) pick parasites from its skin. The spotted tail and fin pattern of the sweetlips signals sexual maturity; the behaviour and pattern of the cleaner fish signal their availability for cleaning service, rather than as prey. (from Animal coloration)
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Image 45Animal anatomical engraving from Handbuch der Anatomie der Tiere für Künstler. (from Zoology)
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Image 46Simplified schematic of an island's fauna – all its animal species, highlighted in boxes (from Fauna)
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Image 47Conrad Gessner (1516–1565). His Historiae animalium is considered the beginning of modern zoology. (from Zoology)
The following table lists estimated numbers of described extant species for the animal groups with the largest numbers of species, along with their principal habitats (terrestrial, fresh water, and marine), and free-living or parasitic ways of life. 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. 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.
| Phylum
|
Example
|
No. of
Species
|
Land
|
Sea
|
Fresh
water
|
Free-
living
|
Parasitic
|
| Annelids
|
|
17,000
|
Yes (soil)
|
Yes
|
1,750
|
Yes
|
400
|
| Arthropods
|
|
1,257,000
|
1,000,000
(insects)
|
>40,000
(Malac-
ostraca)
|
94,000
|
Yes
|
>45,000
|
| Bryozoa
|
|
6,000
|
|
Yes
|
60–80
|
Yes
|
|
| Chordates
|
|
65,000
45,000
|
23,000
|
13,000
|
18,000
9,000
|
Yes
|
40
(catfish)
|
| Cnidaria
|
|
16,000
|
|
Yes
|
Yes (few)
|
Yes
|
>1,350
(Myxozoa)
|
| Echinoderms
|
|
7,500
|
|
7,500
|
|
Yes
|
|
| Molluscs
|
|
85,000
107,000
|
35,000
|
60,000
|
5,000
12,000
|
Yes
|
>5,600
|
| Nematodes
|
|
25,000
|
Yes (soil)
|
4,000
|
2,000
|
11,000
|
14,000
|
| Platyhelminthes
|
|
29,500
|
Yes
|
Yes
|
1,300
|
Yes
3,000–6,500
|
>40,000
4,000–25,000
|
| Rotifers
|
|
2,000
|
|
>400
|
2,000
|
Yes
|
|
| Sponges
|
|
10,800
|
|
Yes
|
200-300
|
Yes
|
Yes
|
Total number of described extant species as of 2013: 1,525,728
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