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 behaviors is known as
ethology.
The thylacine (/ˈθaɪləsiːn/;
binomial nameThylacinus cynocephalus), also commonly known as the Tasmanian tiger or Tasmanian wolf, is an
extinct carnivorous
marsupial that was native to the
Australian mainland and the islands of
Tasmania and
New Guinea. The thylacine died out in New Guinea and mainland Australia around 3,600–3,200 years ago, prior to the arrival of Europeans, possibly because of the introduction of the
dingo, whose earliest record dates to around the same time, but which never reached Tasmania. Prior to European settlement, around 5,000 remained in the wild on Tasmania. Beginning in the nineteenth century, they were perceived as a threat to the livestock of farmers and
bounty hunting was introduced. The last known of its species died in 1936 at
Hobart Zoo in Tasmania. The thylacine is widespread in popular culture and is a
cultural icon in Australia.
The thylacine was known as the Tasmanian tiger because of the dark transverse stripes that radiated from the top of its back, and it was called the Tasmanian wolf because it resembled a medium- to large-sized
canid. The name thylacine is derived from thýlakos meaning "pouch" and ine meaning "pertaining to", and refers to the
marsupial pouch. Both sexes had a pouch. The females used theirs for rearing young, and the males used theirs as a protective sheath, covering the
external reproductive organs. The animal had a stiff tail and could open its jaws to an unusual extent. Recent studies and anecdotal evidence on its predatory behaviour suggest that the thylacine was a solitary
ambush predator specialised in hunting small to medium-sized prey. Accounts suggest that in the wild, it fed on small birds and mammals. It was the only member of the genus Thylacinus and family
Thylacinidae to have survived until modern times. Its closest living relatives are the other members of
Dasyuromorphia including the
Tasmanian devil, from which it is estimated to have split 42–36 million years ago. (Full article...)
Anatomical diagram of an adult female
chambered nautilus, the best known species of nautilus, a "
living fossil" related to the octopuses. The animal has a primitive brain that forms a ring around its
oesophagus, has four gills (all other
cephalopods have only two), and can only move shell-first (seemingly "backwards") by pumping water out through its funnel. The shell and tentacles are shown here as shadows.
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.
Aplysina archeri is a species of
sponge that has long tube-like structures of cylindrical shape. Many tubes are attached to one particular part of the organism; a single tube can grow up to 5 feet (1.5 m) high and 3 inches (7.6 cm) thick. These sponges mostly live in the
Atlantic Ocean. These
filter feeders eat food such as
plankton or suspended
detritus as it passes them.
Haliotis laevigata is a species of marine
mollusc in the family
Haliotidae,
endemic to Tasmania and the southern and western coasts of Australia. This picture shows five views of a green H. laevigata shell, 7.5 centimetres (3.0 in) in length. The holes in the shell, characteristic of
abalones, are respiratory apertures for venting water from the gills and for releasing sperm and eggs into the
water column.
The maxima clam (Tridacna maxima) is a species of
bivalve found throughout the
Indo-Pacific. It is found on the surface of reefs or sand, or partly embedded in coral (as with this specimen), in the oceans surrounding east Africa, India, China, Australia, Southeast Asia and the islands of the Pacific. This clam is much sought after in the aquarium trade, as its often striking coloration—the result of crystalline pigment—mimics that of the true
giant clam.
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.
Cymbiola nobilis is a species of
sea snail in the
familyVolutidae. Found in the Pacific Ocean, from Taiwan to Singapore, it averages 6 centimetres (2.4 in) in length; females are
larger than males. Because the shell is commonly collected, there has been an overharvesting of the snail, and it is now considered
vulnerable.
The leopard shark (Triakis semifasciata) is a species of
hound shark found along the
Pacific coast of
North America from the U.S. state of
Oregon to
Mazatlán in Mexico. Typically measuring 1.2–1.5 m (3.9–4.9 ft) long, this slender-bodied shark is characterized by black saddle-like markings and large spots over its back.
Liguus virgineus, also known as the candy cane snail, is a species of snail in the family
Orthalicidae. It is native to the Caribbean island of
Hispaniola, in the nations of Haiti and the Dominican Republic. There have also been at least three reports of living specimens being found in the
Florida Keys of the United States. The snail lives on trees and feeds on moss, fungi and microscopic algae covering the bark.
Brittle stars, serpent stars, or ophiuroids (from
Latin ophiurus 'brittle star'; from
Ancient Greekὄφις (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...)
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.
A cross section of a post-
clitellum segment of an annelid (ringed worm); almost all segments of an annelid contain the same set of organs and parts, a pattern called
metamerism. Annelids have no lungs, but rather exchange
carbon dioxide and
oxygen directly through the moist skin when blood reaches the extremely fine capillaries of the body walls; a dry worm cannot breathe and will die of suffocation. The worm's red blood, which does not consist of
platelets or
red cells but mostly of a liquid containing suspended
hemoglobin, makes a circuit up and down the animal in its closed circulatory systems.
The flatworms, flat worms, Platyhelminthes, or platyhelminths (from the
Greek πλατύ, platy, meaning "flat" and ἕλμινς (root: ἑλμινθ-), helminth-, meaning "worm") are a
phylum of relatively simple
bilaterian,
unsegmented, soft-bodied
invertebrates. Unlike other bilaterians, they are
acoelomates (having no
body cavity), and have no specialised
circulatory and
respiratoryorgans, which restricts them to having flattened shapes that allow
oxygen and nutrients to pass through their bodies by
diffusion. The digestive cavity has only one opening for both ingestion (intake of nutrients) and egestion (removal of undigested wastes); as a result, the food cannot be processed continuously. (Full article...)
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Bharattherium is a
mammal that lived in
India during the
Maastrichtian (latest
Cretaceous) and possibly the
Paleocene. The
genus has a single
species, Bharattherium bonapartei. It is part of the
gondwanathere family
Sudamericidae, which is also found in Madagascar and South America during the latest Cretaceous. The first fossil of Bharattherium was discovered in 1989 and published in 1997, but the animal was not named until 2007, when two teams independently named the animal Bharattherium bonapartei and Dakshina jederi. The latter name is now a
synonym. Bharattherium is known from a total of eight isolated fossil teeth, including one
incisor and seven molariforms (
molar-like teeth, either
premolars or true molars).
Bharattherium molariforms are high, curved teeth, with a height of 6 to 8.5 millimetres (0.24 to 0.33 in). In a number of teeth tentatively identified as fourth lower molariforms (mf4), there is a large furrow on one side and a deep cavity (infundibulum) in the middle of the tooth. Another tooth, perhaps a third lower molariform, has two furrows on one side and three infundibula on the other. The
tooth enamel has traits that have been interpreted as protecting against cracks in the teeth. The
hypsodont (high-crowned) teeth of sudamericids like Bharattherium are reminiscent of later grazing mammals, and the discovery of grass in Indian fossil sites contemporaneous with those yielding Bharattherium suggest that sudamericids were indeed grazers. (Full article...)
Image 3Bright coloration of orange elephant ear sponge, Agelas clathrodes signals its bitter taste to predators (from Animal coloration)
Image 4The 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)
Image 28A
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)
Image 30Idealised
bilaterian 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)
Image 31Kelp gull chicks peck at red spot on mother's beak to stimulate the regurgitating reflex. (from Zoology)
Image 32A
gun dog retrieving a duck during a hunt (from Animal)
Image 37A 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)
Image 46Linnaeus's table of the animal kingdom from the first edition of Systema Naturae (1735) (from Zoology)
Image 47Non-bilaterians include sponges (centre) and corals (background). (from Animal)
Image 48The bilaterian gut develops in two ways. In many
protostomes, the blastopore develops into the mouth, while in
deuterostomes it becomes the anus. (from Animal)
Image 49Butterfly wing at different magnifications reveals microstructured chitin acting as diffraction grating. (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]
^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]
^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.
PMID28938083.
S2CID23755007. Stork notes that 1m insects have been named, making much larger predicted estimates.
^
abcdNicol, David (June 1969). "The Number of Living Species of Molluscs". Systematic Zoology. 18 (2): 251–254.
doi:
10.2307/2412618.
JSTOR2412618.
^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.
S2CID38784755.