Smallest organisms
The smallest organisms found on Earth can be determined according to various aspects of organism size, including volume, mass, height, length, or genome size.
Given the incomplete nature of scientific knowledge, it is possible that the smallest organism is undiscovered. Furthermore, there is some debate over the definition of life, and what entities qualify as organisms; consequently the smallest known organism is debatable.
Microorganisms
Viruses
Many biologists consider viruses to be non-living because they lack a cellular structure and cannot metabolize by themselves, requiring a host cell to replicate and synthesize new products. A minority of scientists hold that, because viruses do have genetic material and can employ the metabolism of their host, they can be considered organisms. Also, an emerging concept that is gaining traction among some virologists is that of the virocell, in which the actual phenotype of a virus is the infected cell, and the virus particle is merely a reproductive or dispersal stage, much like pollen or a spore.The smallest viruses in terms of genome size are single-stranded DNA viruses. Perhaps the most famous is the bacteriophage Phi-X174 with a genome size of 5386 nucleotides. However, some ssDNA viruses can be even smaller. For example, Porcine circovirus type 1 has a genome of 1759 nucleotides and a capsid diameter of 17 nm. As a whole, the viral family geminiviridae is about 30 nm in length. However, the two capsids making up the virus are fused; divided, the capsids would be 15 nm in length. Other environmentally characterized ssDNA viruses such as CRESS DNA viruses, among others, can have genomes that are considerably less than 2,000 nucleotides.
The smallest RNA viruses in terms of genome size are small retroviruses such as rous sarcoma virus with genomes of 3.5 kilo base pairs and particle diameters of 80 nanometres. The smallest double-stranded DNA viruses are the hepadnaviruses such as Hepatitis B, at 3.2 kb and 42 nm; parvoviruses have smaller capsids, at 18-26 nm, but larger genomes, at 5 kb. It is important to consider other self-replicating genetic elements, such as satelliviruses, viroids and ribozymes.
Obligate endosymbiotic bacteria
The genome of Nasuia deltocephalinicola, a symbiont of the European pest leafhopper, Macrosteles quadripunctulatus, consists of a circular chromosome of 112,031 base pairs.The genome of Nanoarchaeum equitans is 490,885 nucleotides long.
''Pelagibacter ubique''
Pelagibacter ubique is one of the smallest known free-living bacteria, with a length of 370 to 890 nm and an average cell diameter of 120 to 200 nm. They also have the smallest free-living bacterium genome: 1.3Mbp, 1354 protein genes, 35 RNA genes. They are one of the most common and smallest organisms in the ocean, with their total weight exceeding that of all fish in the sea.''Mycoplasma genitalium''
Mycoplasma genitalium, a parasitic bacterium which lives in the primate bladder, waste disposal organs, genital, and respiratory tracts, is thought to be the smallest known organism capable of independent growth and reproduction. With a size of approximately 200 to 300 nm, M. genitalium is an ultramicrobacterium, smaller than other small bacteria, including rickettsia and chlamydia. However, the vast majority of bacterial strains have not been studied, and the marine ultramicrobacterium Sphingomonas sp. strain RB2256 is reported to have passed through a 220 nm ultrafilter. A complicating factor is nutrient-downsized bacteria, bacteria that become much smaller due to a lack of available nutrients.and archaeon host, Ignicoccus''
''Nanoarchaeum''
Nanoarchaeum equitans is a species of microbe 200 to 500 nm in diameter. It was discovered in 2002 in a hydrothermal vent off the coast of Iceland by Karl Stetter. A thermophile that grows in near-boiling temperatures, Nanoarchaeum appears to be an obligatory symbiont on the archaeon Ignicoccus; it must be in contact with the host organism to survive.Eukaryotes
e of the genus Ostreococcus are the smallest free-living eukaryote. The single cell of an Ostreococcus measures 0.8 μm across.Animals
Several species of Myxozoa never grow larger than 20 µm. One of the smallest species is no more than 8.5 µm when fully grown.[Molluscs]
[Bivalvia]
The shell of the nut clam Condylonucula maya grows 0.54 mm long.[Gastropods]
The smallest water snail is Ammonicera minortalis in North America, originally described from Cuba. It measures 0.32 to 0.46 mm.The smallest land snail is Acmella nana. Discovered in Borneo, and described in November 2015, it measures 0.7 mm. The previous record was that of Angustopila dominikae from China, which was reported in September 2015. This snail measures 0.86 mm.
[Arthropods]
Smallest crustacean
The smallest crustacean, and indeed the smallest arthropod, is the tantulocarid Stygotantulus stocki, at a length of.[Arachnids]
The smallest arachnids are mites of the family Microdispidae, Cochlodispus minimus, at 79 µm long.Insects
Adult males of the parasitic wasp Dicopomorpha echmepterygis can be as small as 139 μm long, smaller than some species of protozoa ; females are 40% larger.Megaphragma caribea from Guadeloupe, measuring 170 μm long, is another contender for smallest known insect in the world.
- Beetles
- Butterflies
The western pygmy blue is one of the smallest butterflies in the world, with a wingspan of about 1 centimetre.
Echinoderms
The smallest sea cucumber, and also the smallest echinoderm, is Psammothuria ganapati, a synaptid that lives between sand grains on the coast of India. Its maximum length is 4 mm.Sea urchins
The smallest sea urchin, Echinocyamus scaber, has a test 6 mm across.Starfish
Patiriella parvivipara is the smallest starfish, at 5 mm across.Vertebrates
The smallest vertebrates known are Paedophryne amauensis frogs from Papua New Guinea, which range in length from, and average. Previously, the title of smallest vertebrate was held by members of the fish genus Paedocypris of Indonesia.Fish
One of the smallest fish based on the minimum size at maturity is Paedocypris progenetica from Indonesia, with mature females measuring as little as in standard length. This fish, a member of the carp family, has a translucent body and a head unprotected by a skeleton.One of smallest fish based on the minimum size at maturity is Schindleria brevipinguis from Australia, their females reach 7 mm and males 6.5 mm, Males of S. brevipinguis have an average standard length of ; a gravid female was. This fish, a member of the goby family, differs from similar members of the group in having its first anal fin ray further forward, under dorsal fin 4.
Male individuals of the anglerfish species Photocorynus spiniceps have been documented to be at maturity, and thus claimed to be a smaller species. However, these survive only by sexual parasitism and the female individuals reach the significantly larger size of.
Amphibians
Salamanders
The average snout-to-vent length of several specimens of the salamander Thorius arboreus was.Frogs
Frogs include the smallest vertebrates known. The smallest known frog species is Paedophryne amauensis, with a snout-vent length reported as 7.7 mm, which occurs among leaf-litter in the tropical montane forests of New Guinea. Other very small frogs include Brachycephalus didactylus from Brazil, several species of Eleutherodactylus such as E. iberia and E. limbatus and Eleutherodactylus orientalis from Cuba, Gardiner's Frog Sechellophryne gardineri from the Seychelles, several species of Stumpffia such as S. tridactyla and S. pygmaea and Wakea madinika from Madagascar. Paedophryne swiftorum is not included in the smallest vertebrates known with other nine species of frogs. The two species Microhyla borneensis and Arthroleptella rugosa were once the smallest known frogs from the Old World. In general these extremely small frogs occur in tropical forest and montane environments. There is relatively little data on size variation among individuals, growth from metamorphosis to adulthood or size variation among populations in these species. Additional studies and the discovery of further minute frog species are likely to change the rank order of this list.Reptiles
Lizards
Two geckos, the dwarf gecko and the Virgin Islands dwarf sphaero, are the smallest known reptile species and smallest lizard, with a snout-vent length of. A few Brookesia chameleons from Madagascar are equally small, with a reported snout-vent length of 15–18 mm for male dwarf chameleons, 14–19 mm for male Mount d'Ambre leaf chameleons and 15–16 mm for male B. micra, though females are larger.Of the aforementioned geckos, S. ariasae was first described in 2001 by the biologists Blair Hedges and Richard Thomas. This dwarf gecko lives in Jaragua National Park in the Dominican Republic and on Beata Island, off the southern coast of the Dominican Republic.
Turtles
The smallest turtle is the speckled padloper tortoise from South Africa. The males measure, while females measure up to almost.Crocodilians
The smallest crocodilian is the Cuvier's dwarf caiman from northern and central South America. It reaches up to in length.Snakes
One of the smallest snakes known is the recently discovered Barbados threadsnake. Adults average about long, which is only about twice as long as the hatchlings. The Common blind snake measures long, occasionally up to long.Dinosaurs
The smallest avian dinosaur is the bee hummingbird. The smallest known extinct dinosaur is Anchiornis, a genus of feathered dinosaur that lived in what is now China during the Late Jurassic Period 160 to 155 million years ago. Adult specimens range from long, and the weight has been estimated at up to. Nevertheless, sizes of dinosaurs are commonly labelled with a level of uncertainty, as the available material often is incomplete. Oculudentavis is even smaller than Anchiornis, but it is uncertain if it is in fact an dinosaur.Birds
With a mass of approximately and a length of 5 centimetres, the bee hummingbird is the smallest bird species, the smallest warm-blooded vertebrate, and smallest known dinosaur. Called the zunzún in its native habitat on Cuba, it is lighter than a Canadian or U.S. penny. It is said that it is "more apt to be mistaken for a bee than a bird". The bee hummingbird eats half its total body mass and drinks eight times its total body mass each day. Its nest is 3 cm across.Mammals
The vulnerable Kitti's hog-nosed bat, also known as the bumblebee bat, from Thailand and Myanmar is the smallest mammal, at in length and in weight.The Etruscan shrew, is the smallest mammal by mass, weighing about on average. The bumblebee bat has a smaller skull size. The smallest mammal that ever lived, the shrew-like Batodonoides vanhouteni, weighed.
Rodents
The smallest known member of the rodent order is the Baluchistan pygmy jerboa, with an average body length of 4.4 cm.Carnivorans
The smallest member of the order Carnivora is the least weasel, with an average body length of 114–260 mm. It weighs between 29.5 – 250 grams with females being lighter.Marsupials
The smallest marsupial is the long-tailed planigale from Australia. It has a body length of and weigh on average.The Pilbara ningaui is considered to be of similar size and weight.
Primates
The smallest member of the primate order is Madame Berthe's mouse lemur, found in Madagascar, with an average body length of 92 mm.Cetaceans
The smallest cetacean, which is also the most endangered, is the vaquita. Male vaquitas grow to an average of around 135 cm ; the females are slightly longer, averaging about 141 cm in length.Plants
Flowering plants (angiosperms)
s of the genus Wolffia are the smallest flowering plants. Fully grown, they measure 300 µm by 600 µm and reach a mass of just 150 µg.Other
Nanobes
s are thought by some scientists to be the smallest known organisms,about one tenth the size of the smallest known bacteria. Nanobes, tiny filamental structures first found in some rocks and sediments, were first described in 1996 by Philippa Uwins of the University of Queensland.