Over 1.5 millionlivinganimalspecieshave beendescribed,of which around 1.05 million areinsects,over 85,000 aremolluscs,and around 65,000 arevertebrates.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 complexecologiesandinteractionswith each other and their environments, forming intricatefood webs.The scientific study of animals is known aszoology,and the study of animal behaviors is known asethology.
Leechesare segmentedparasiticorpredatorywormsthat comprise thesubclassHirudineawithin thephylumAnnelida.They are closely related to theoligochaetes,which include theearthworm,and like them have soft, muscular segmented bodies that can lengthen and contract. Both groups arehermaphroditesand have aclitellum,but leeches typically differ from the oligochaetes in having suckers at both ends and in having ring markings that do not correspond with their internal segmentation. The body is muscular and relatively solid, and thecoelom,the spacious body cavity found in other annelids, is reduced to small channels.
The majority of leeches live in freshwater habitats, while some species can be found in terrestrial or marine environments. The best-known species, such as the medicinal leech,Hirudo medicinalis,arehematophagous,attaching themselves to a host with a sucker and feeding on blood, having first secreted the peptidehirudinto prevent the blood from clotting. The jaws used to pierce the skin are replaced in other species by aprobosciswhich is pushed into the skin. A minority of leech species are predatory, mostly preying on small invertebrates. (Full article...)
A caterpillar ofLymantria dispar dispar,also known as the gypsy moth. First described byCarl Linnaeusin 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 initiallydiurnal,but becomenocturnalafter their fourth molting.
Thegolden toad(Bufo periglenes) is anextinctspecies oftrue toadthat was once abundant in a small region of high-altitude cloud-coveredtropical forests,about 30 km2(12 sq mi) in area, above the city ofMonteverde,Costa Rica. The last reported sighting of a golden toad was on15 May1989. Its sudden extinction may have been caused bychytrid fungusand extensivehabitat loss.
Thesperm whaleis the largest toothed animal on Earth. The species was hunted extensively by humans throughout history, until protected by aworldwide moratorium on whalingstarting in 1985–86.
Plate 5 fromErnst Haeckel'sKunstformen der Natur,showing a variety ofcalcareous sponges,aclassof about 400 marinespongesthat 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.
Aplysina archeriis a species ofspongethat 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 theAtlantic Ocean.Thesefilter feederseat food such asplanktonor suspendeddetritusas it passes them.
Cymbiola nobilisis a species ofsea snailin thefamilyVolutidae.Found in the Pacific Ocean, from Taiwan to Singapore, it averages 6 centimetres (2.4 in) in length; females arelarger than males.Because the shell is commonly collected, there has been an overharvesting of the snail, and it is now consideredvulnerable.
Bolinus cornutusis a predatoryspeciesofsea snail,a marinegastropodmolluskin thefamilyMuricidae.This species is common along the west coast of Africa, where it prefers moderately shallow waters. The shell of the snail is distinctively large, spiny, and club-shaped, usually pale brown or tan in colour, with an elongated and straightsiphonal canal.
TheCommon Brushtail Possum(Trichosurus vulpecula) is the largestpossumspecies and is perhaps the most widespreadmammalin Australia. It grows to about 32–58 cm (13–23 in) in length, with an additional 24–40 cm (9–16 in) for itsprehensiletail (seen here hanging below the branch). It is mainly afolivore,but has been known to eat small mammals such as rats. It is common in cities, having adapted well to human habitation.
Theflatworms,flat worms,Platyhelminthes,orplatyhelminths(from theGreekπλατύ,platy,meaning "flat" and ἕλμινς (root: ἑλμινθ-),helminth-,meaning "worm") are aphylumof relatively simplebilaterian,unsegmented,soft-bodiedinvertebrates.Beingacoelomates(having nobody cavity), and having no specialisedcirculatoryandrespiratoryorgans,they are restricted to having flattened shapes that allowoxygenand nutrients to pass through their bodies bydiffusion.The digestive cavity has only one opening for both ingestion (intake of nutrients) and egestion (removal of undigested wastes); as a result, thefoodcan not be processed continuously. (Full article...)
Amacroview of aGonia capitataflyfeeding onhoney,showing itsproboscisandpedipalps(the two appendages protruding from the proboscis), two types ofinsect mouthparts.The proboscis actually comprises the labium, a quadrupedal structure, and a sponge-like labellum at the end. Flies eat solid food by secretingsalivaand dabbing it over the food item. As the saliva dissolves the food, the solution is then drawn up into the mouth as a liquid. The labellum's surface is covered by minute food channels which form a tube leading to theesophagus,and food is drawn up the channels bycapillary action.
Bryozoa(also known as thePolyzoa,Ectoproctaor commonly asmoss animals) are aphylumof simple,aquaticinvertebrateanimals, nearly all living in sedentarycolonies.Typically about0.5 millimetres (1⁄64in) long, they have a special feeding structure called alophophore,a "crown" of tentacles used forfilter feeding.Mostmarinebryozoans live in tropical waters, but a few are found inoceanic trenchesand polar waters. The bryozoans are classified as themarine bryozoans(Stenolaemata),freshwater bryozoans(Phylactolaemata), andmostly-marine bryozoans(Gymnolaemata), a few members of which preferbrackish water.5,869living species 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 has been described in fourgenera;Aethozooides,Aethozoon,FranzenellaandMonobryozoon). The latter having a statocyst‐like organ with a supposed excretory function. (Full article...)
Sexual dimorphismis the condition where the twosexesof the samespeciesexhibit different characteristics. Differences may includesecondary sex characteristics,size, weight, color, or markings, as well as behavioral and cognitive differences. In the butterfly speciesColias 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.
An illustration of variousPulmonata(and one predatorarthropodin the lower right), an informal group ofsnailsandslugscharacterized by the ability to breathe air, by virtue of having apallial lunginstead of agill,or gills. Pulmonata was previously a formaltaxonbut lost its status as one in 2010. The group includes many land and freshwater families, and several marine families. Most species have a shell, but nooperculum,although the group does also include several shell-less slugs. Pulmonates arehermaphroditic,and some groups possesslove darts.
Coralsaremarine invertebratesthat typically live in compactcoloniesof many identical individualpolyps.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 thecoral reefssuch as theGreat Barrier Reef,where this photograph was taken. Coral reefs are under threat globally fromocean acidificationandclimate change.
A lateral (left side) anatomical diagram of an adult-stage nematodehermaphroditeCaenorhabditis elegans(full size) with emphasis on the digestive and reproductive systems.C. elegansis a free-living, transparentnematode(roundworm) which measures about 1 millimetre (0.039 in) in length. The hermaphrodite form, as seen here, is the most common, although a male form is also found. When self-inseminated, the species will lay about 300 eggs, but when the hermaphrodite is inseminated by a male, the number of progeny can exceed 1,000.
Brittle stars,serpent stars,orophiuroids(fromLatinophiurus'brittle star'; fromAncient Greekὄφις(óphis)'serpent', andοὐρά(ourá)'tail'; referring to the serpent-like arms of the brittle star) areechinodermsin the classOphiuroidea,closely related tostarfish.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...)
Rodents(fromLatinrodere,'to gnaw') aremammalsof theorderRodentia(/roʊˈdɛnʃə/roh-DEN-shə), which are characterized by a single pair of continuously growingincisorsin each of the upper and lowerjaws.About 40% of all mammal species are rodents. They are native to all major land masses except forAntarctica,and several oceanic islands, though they have subsequently been introduced to most of these land masses by human activity.
Rodents are extremely diverse in their ecology and lifestyles and can be found in almost every terrestrial habitat, including human-made environments. Species can bearboreal,fossorial(burrowing),saltatorial/richochetal (leaping on their hind legs), or semiaquatic. However, all rodents share several morphological features, including having only a single upper and lower pair of ever-growing incisors. Well-known rodents includemice,rats,squirrels,prairie dogs,porcupines,beavers,guinea pigs,andhamsters.Rabbits,hares,andpikas,which also have incisors that grow continuously (but have two pairs of upper incisors instead of one), were once included with rodents, but are now considered to be in a separate order, theLagomorpha.Nonetheless, Rodentia and Lagomorpha aresister groups,sharing asingle common ancestorand forming thecladeofGlires.(Full article...)
...thatCaecillians,an order ofamphibiansresembling snakes or worms, possess a pair of tentacles, located between their eyes and nostrils which are probably used forolfaction?
The following are images from various animal-related articles on Wikipedia.
Image 1The bilaterian gut develops in two ways. In manyprotostomes,the blastopore develops into the mouth, while indeuterostomesit becomes the anus. (fromAnimal)
Image 2Simplified schematic of an island's fauna – all its animal species, highlighted in boxes (fromFauna)
Image 3A clade representation of seven dog breeds in relation to wolves. (fromZoology)
Image 4Linnaeus's table of the animal kingdom from the first edition ofSystema Naturae(1735) (fromZoology)
Image 5Squidchromatophores appear as black, brown, reddish and pink areas in this micrograph. (fromAnimal coloration)
Image 6The microscopic cave snailZospeum tholussum,found at depths of 743 to 1,392 m (2,438 to 4,567 ft) in theLukina Jama–Trojamacave system ofCroatia,is completely blind with a translucent shell (fromFauna)
Image 13A brilliantly-colouredoriental sweetlipsfish (Plectorhinchus vittatus) waits while two boldly-patternedcleaner 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 thecleaner fishsignal their availability forcleaning service,rather than as prey (fromAnimal coloration)
Image 45Apraying mantisindeimaticor threat pose displays conspicuous patches of colour to startle potential predators. This is not warning coloration as the insect is palatable. (fromAnimal coloration)
Image 47Idealisedbilaterianbody plan. With an elongated body and a direction of movement the animal has head and tail ends. Sense organs and mouth form thebasis of the head.Opposed circular and longitudinal muscles enableperistaltic motion.(fromAnimal)
Image 48The black and yellow warning colours of the cinnabar moth caterpillar,Tyria jacobaeae,are avoided by some birds. (fromAnimal 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 thetaxonomichierarchy, 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 ofDNA barcodingto taxonomy further complicates this; a 2016 barcoding analysis estimated a total count of nearly 100,000insectspecies forCanadaalone, 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.
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