Animals are multicellular, eukaryotic organisms comprising 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 sea otter (Enhydra lutris) is a marine mammal native to the coasts of the northern and eastern North Pacific Ocean. Adult sea otters typically weigh between 14 and 45 kg (30–100 lb), making them the heaviest members of the weasel family, but among the smallest marine mammals. Unlike most marine mammals, the sea otter's primary form of insulation is an exceptionally thick coat of fur, the densest in the animal kingdom. Although it can walk on land, the sea otter is capable of living exclusively in the ocean.
The sea otter inhabits nearshore environments, where it dives to the sea floor to forage. It preys mostly on marine invertebrates such as sea urchins, various mollusks and crustaceans, and some species of fish. Its foraging and eating habits are noteworthy in several respects. Its use of rocks to dislodge prey and to open shells makes it one of the few mammal species to use tools. In most of its range, it is a keystone species, controlling sea urchin populations which would otherwise inflict extensive damage to kelp forest ecosystems. Its diet includes prey species that are also valued by humans as food, leading to conflicts between sea otters and fisheries. (Full article...)
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Image 1Photograph 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 2Photograph credit: Charles J. Sharp The paddyfield pipit ( Anthus rufulus) is a passerine bird in the family Motacillidae, comprising pipits, longclaws and wagtails. About 15 cm (6 in) in length and native to southern Asia, its plumage in both sexes is greyish-brown above and paler yellowish-brown below, with dark streaking on the breast. A bird of open country, pasture and cultivated fields, it sometimes makes short flights, but mostly runs on the ground, foraging for insects and other small invertebrates. The paddyfield pipit builds its cup-shaped nest in a concealed location on the ground, and may have two or more broods in a year. This A. r. rufulus individual was photographed in Kanha Tiger Reserve, in the Indian state of Madhya Pradesh.
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Image 3Brittle 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 6Bryozoa (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 7Credit: Twilight Zone Expedition Team 2007, NOAA-OE Sponges or sea sponges are primarily marine invertebrates of the animal phylum Porifera (; meaning 'pore bearer'), a basal clade and a sister taxon of the diploblasts. They are sessile filter feeders that are bound to the seabed, and are one of the most ancient members of macrobenthos, with many historical species being important reef-building organisms. ( Full article...) Included are the yellow tube sponge, Aplysina fistularis, the purple vase sponge, Niphates digitalis, the red encrusting sponge, Spirastrella coccinea, and the gray rope sponge, Callyspongia sp.
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Image 10Photograph: 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 12The 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 13Photo: Charles H. Smith, USFWS
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Image 14Photograph: Kateshortforbob
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Image 15Illustration: Comingio Merculiano
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Image 17The coconut octopus ( Amphioctopus marginatus) is a medium-sized cephalopod found in tropical waters of the western Pacific Ocean. It commonly preys upon shrimp, crabs, and clams, and displays unusual behaviour, including bipedal walking and gathering and using coconut shells and seashells for shelter.
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Image 18A soybean cyst nematode ( Heterodera glycines), together with an egg, as viewed through a low-temperature scanning electron microscope at 1000x magnification. This nematode infects the roots of soybeans, and the female nematode eventually becomes a cyst. Infection causes various symptoms that may include chlorosis of the leaves and stems, root necrosis, loss in seed yield and suppression of root and shoot growth.
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Image 20Photograph: Gabriel Barathieu
Selected article - Entries here consist of Good and Featured articles, which meet a core set of high editorial standards.
Animal coloration is the general appearance of an animal resulting from the reflection or emission of light from its surfaces. Some animals are brightly coloured, while others are hard to see. In some species, such as the peafowl, the male has strong patterns, conspicuous colours and is iridescent, while the female is far less visible.
There are several separate reasons why animals have evolved colours. Camouflage enables an animal to remain hidden from view. Animals use colour to advertise services such as cleaning to animals of other species; to signal their sexual status to other members of the same species; and in mimicry, taking advantage of the warning coloration of another species. Some animals use flashes of colour to divert attacks by startling predators. Zebras may possibly use motion dazzle, confusing a predator's attack by moving a bold pattern rapidly. Some animals are coloured for physical protection, with pigments in the skin to protect against sunburn, while some frogs can lighten or darken their skin for temperature regulation. Finally, animals can be coloured incidentally. For example, blood is red because the haem pigment needed to carry oxygen is red. Animals coloured in these ways can have striking natural patterns. (Full article...)
The following are images from various animal-related articles on Wikipedia.
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Image 1Idealised 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 2Predators, such as this ultramarine flycatcher ( Ficedula superciliaris), feed on other animals. (from Animal)
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Image 3Artistic vision: Still Life with Lobster and Oysters by Alexander Coosemans, c. 1660 (from Animal)
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Image 4Animals 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 5The brilliant iridescent colours of the peacock's tail feathers are created by Structural coloration. (from Animal coloration)
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Image 6Butterfly wing at different magnifications reveals microstructured chitin acting as diffraction grating. (from Animal coloration)
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Image 7Simplified schematic of an island's fauna – all its animal species, highlighted in boxes (from Fauna)
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Image 8The Spiralia develop with spiral cleavage in the embryo, as here in a sea snail. (from Animal)
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Image 9Non-bilaterians include sponges (centre) and corals (background). (from Animal)
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Image 10The 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 11Linnaeus's table of the animal kingdom from the first edition of Systema Naturae (1735) (from Zoology)
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Image 12This frog changes its skin colour to control its temperature. (from Animal coloration)
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Image 13A 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 14Animal anatomical engraving from Handbuch der Anatomie der Tiere für Künstler. (from Zoology)
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Image 15The 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 16A camouflaged orange oak leaf butterfly, Kallima inachus (centre) has protective resemblance. (from Animal coloration)
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Image 17Hydrothermal vent mussels and shrimps (from Animal)
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Image 18A venomous coral snake uses bright colours to warn off potential predators. (from Animal coloration)
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Image 19Robert Hooke's Micrographia (from Animal coloration)
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Image 20Bright coloration of orange elephant ear sponge, Agelas clathrodes signals its bitter taste to predators (from Animal coloration)
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Image 21Male Goldie's bird-of-paradise displays to a female (from Animal coloration)
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Image 22A gun dog retrieving a duck during a hunt (from Animal)
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Image 23Myxozoans such as Myxobolus cerebralis are single-celled parasites, never more than 20 μm across. (from Animal)
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Image 24The 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 26The 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 27Jean-Baptiste de Lamarck led the creation of a modern classification of invertebrates, breaking up Linnaeus's "Vermes" into 9 phyla by 1809. (from Animal)
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Image 28Conrad Gessner (1516–1565). His Historiae animalium is considered the beginning of modern zoology. (from Zoology)
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Image 29The olm's blood makes it appear pink. (from Animal coloration)
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Image 31Warning coloration of the skunk in Edward Bagnall Poulton's The Colours of Animals, 1890 (from Animal coloration)
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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 33Kelp gull chicks peck at red spot on mother's beak to stimulate the regurgitating reflex. (from Zoology)
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Image 34Sides of beef in a slaughterhouse (from Animal)
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Image 35Squid chromatophores appear as black, brown, reddish and pink areas in this micrograph. (from Animal coloration)
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Image 37Sexual reproduction is nearly universal in animals, such as these dragonflies. (from Animal)
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Image 38Papuan, 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 39Side 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 40The 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 41Fish and frog melanophores are cells that can change colour by dispersing or aggregating pigment-containing bodies. (from Animal coloration)
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Image 42Examples of fauna in Olleros de Tera ( Spain) (from Fauna)
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Image 44In 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 45A clade representation of seven dog breeds in relation to wolves. (from Zoology)
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Image 46The black and yellow warning colours of the cinnabar moth caterpillar, Tyria jacobaeae, are avoided by some birds. (from Animal coloration)
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
|
|
17,000[1]
|
Yes (soil)[3]
|
Yes[3]
|
1,750[2]
|
Yes
|
400[4]
|
| Arthropods
|
|
1,257,000[1]
|
1,000,000
(insects)[9]
|
>40,000
(Malac-
ostraca)[10]
|
94,000[2]
|
Yes[3]
|
>45,000[b][4]
|
| Bryozoa
|
|
6,000[1]
|
|
Yes[3]
|
60–80[2]
|
Yes
|
|
| Chordates
|
|
65,000[1]
45,000[11]
|
23,000[11]
|
13,000[11]
|
18,000[2]
9,000[11]
|
Yes
|
40
(catfish)[12][4]
|
| Cnidaria
|
|
16,000[1]
|
|
Yes[3]
|
Yes (few)[3]
|
Yes[3]
|
>1,350
(Myxozoa)[4]
|
| Echinoderms
|
|
7,500[1]
|
|
7,500[1]
|
|
Yes[3]
|
|
| Molluscs
|
|
85,000[1]
107,000[13]
|
35,000[13]
|
60,000[13]
|
5,000[2]
12,000[13]
|
Yes[3]
|
>5,600[4]
|
| Nematodes
|
|
25,000[1]
|
Yes (soil)[3]
|
4,000[5]
|
2,000[2]
|
11,000[5]
|
14,000[5]
|
| Platyhelminthes
|
|
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
|
|
2,000[1]
|
|
>400[16]
|
2,000[2]
|
Yes
|
|
| Sponges
|
|
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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- ^ 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]
- ^ Not including parasitoids.[4]
- ^ 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". Zootaxa. 3703 (1): 5. doi:10.11646/zootaxa.3703.1.3. Archived from the original on 24 April 2019. Retrieved 2 March 2018.
- ^ 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.
- ^ 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.
- ^ 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.
- ^ 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.
- ^ "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.
- ^ 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.
- ^ 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.
- ^ 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.
- ^ Poore, Hugh F. (2002). "Introduction". Crustacea: Malacostraca. Zoological catalogue of Australia. Vol. 19.2A. CSIRO Publishing. pp. 1–7. ISBN 978-0-643-06901-5.
- ^ 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.
- ^ 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.
- ^ 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.
- ^ 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.
- ^ a b Pandian, T. J. (2020). Reproduction and Development in Platyhelminthes. CRC Press. pp. 13–14. ISBN 978-1-000-05490-3.
- ^ 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.
- ^ 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.
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