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 organisms (microrganisms) may be nanobes that can be 20 nanometers long.
The genome of Nasuia deltocephalinicola , a symbiont of the European pest leafhopper, Macrosteles quadripunctulatus , consists of a circular chromosome of 112,031 base pairs. [1]
The genome of Nanoarchaeum equitans is 491 Kbp nucleotides long.[ citation needed ]
Pelagibacter ubique is one of the smallest known free-living bacteria, with a length of 370 to 890 nm (0.00037 to 0.00089 mm) and an average cell diameter of 120 to 200 nm (0.00012 to 0.00020 mm). They also have the smallest free-living bacterium genome: 1.3 Mbp, 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. [2]
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 (0.00022 mm) ultrafilter. A complicating factor is nutrient-downsized bacteria, bacteria that become much smaller due to a lack of available nutrients. [3]
Nanoarchaeum equitans is a species of microbe 200 to 500 nm (0.00020 to 0.00050 mm) 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. Guinness World Records recognizes Nanoarchaeum equitans as the smallest living organism.[ citation needed ]
Prasinophyte algae of the genus Ostreococcus are the smallest free-living eukaryote. The single cell of an Ostreococcus measures 800 nm (0.00080 mm) across.[ citation needed ]
Some 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. Some 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 (or virion) is merely a reproductive or dispersal stage, much like pollen or a spore. [4]
The smallest viruses in terms of genome size are single-stranded DNA (ssDNA) viruses. Perhaps the most famous is the bacteriophage Phi-X174 with a genome size of 5,386 nucleotides. [5] However, some ssDNA viruses can be even smaller. For example, Porcine circovirus type 1 has a genome of 1,759 nucleotides [6] and a capsid diameter of 17 nm (1.7×10−5 mm). [7] As a whole, the viral family geminiviridae is about 30 nm (3.0×10−5 mm) in length. However, the two capsids making up the virus are fused; divided, the capsids would be 15 nm (1.5×10−5 mm) 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. [8] [9]
The smallest RNA virus in terms of genome size is phage BZ13 strain T72 at 3,393 nucleotides length. [10] Viruses using both DNA and RNA in their replication (retroviruses) range in size from 7,040 to 12,195 nucleotides. [11] The smallest double-stranded DNA viruses are the hepadnaviruses such as hepatitis B, at 3.2 kb and 42 nm (4.2×10−5 mm); parvoviruses have smaller capsids, at 18–26 nm (1.8×10−5–2.6×10−5 mm), but larger genomes, at 5 kb. It is important to consider other self-replicating genetic elements, such as obelisks, ribozymes, satelliviruses and viroids.[ citation needed ]
Several species of Myxozoa (obligately parasitic cnidarians) never grow larger than 20 μm (0.020 mm). [12] One of the smallest species (Myxobolus shekel) is no more than 8.5 μm (0.0085 mm) when fully grown, making it the smallest known animal. [13]
The shell of the nut clam Condylonucula maya grows 0.54 mm (0.021 in) long. [14]
The smallest water snail (of all snails) is Ammonicera minortalis in North America, originally described from Cuba. It measures 0.32 to 0.46 mm (0.013 to 0.018 in). [15] [16]
The smallest land snail is Acmella nana . Discovered in Borneo, and described in November 2015, it measures 0.7 mm (0.028 in). [17] The previous record was that of Angustopila dominikae from China, which was reported in September 2015. This snail measures 0.86 mm (0.034 in). [18]
Maximites was the smallest known ammonoid. Adult specimens reached only 10 mm (0.39 in) in shell diameter. [19]
The smallest arthropods are crustaceans in the class Tantulocarida. The single smallest species may be Tantulacus dieteri , with a total body length of only 85 micrometres (0.0033 in). [20] Another candidate is Stygotantulus stocki , with a length of 94 micrometres (0.0037 in). [21]
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 (0.16 in). [28] [29]
The smallest sea urchin, Echinocyamus scaber, has a test 6 mm (0.24 in) across. [29]
Patiriella parvivipara is the smallest starfish, at 5 mm (0.20 in) across. [29]
The smallest vertebrates (and smallest amphibians) known are Paedophryne amauensis frogs from Papua New Guinea, which range in length from 7.0–8.0 mm (0.28–0.31 in), and average 7.7 mm (0.30 in). [37] [38] Other very small frogs include:
Paedophryne swiftorum (body length 8.5 mm (0.33 in)) is not included in the smallest vertebrates known with other nine species of frogs. [39] The two species Microhyla borneensis (males: 10.6–13 mm (0.42–0.51 in); females: 16–19 mm (0.63–0.75 in)) [40] [41] and Arthroleptella rugosa (males: 11.9–14.1 mm (0.47–0.56 in); females: 15.5 mm (0.61 in)) 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.
The average snout-to-vent length (SVL) of several specimens of the salamander Thorius arboreus was 17 mm (0.67 in).[ citation needed ]
The smallest turtle is the speckled padloper tortoise (Homopus signatus) from South Africa. The males measure 6–8 cm (2.4–3.1 in), while females measure up to almost 10 cm (3.9 in). [51]
Nemicolopterus was the smallest pterosaur, it reached about 25 cm (9.8 in) in wingspan. [58]
Sizes of non-avian dinosaurs are commonly labelled with a level of uncertainty, as the available material often (or even usually) is incomplete. The smallest known extinct non-avian 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 34 cm (13 in) long, and the weight has been estimated at up to 110 g (3.9 oz). [59] Parvicursor was initially seen as one of the smallest non-avian dinosaurs known from an adult specimen, at 39 cm (15 in) in length, and 162 g (5.7 oz) in weight. [60] However, in 2022 its holotype was concluded to represent a juvenile individual. [61] Epidexipteryx reached 25–30 cm (9.8–11.8 in) in length and 164–220 g (5.8–7.8 oz) in weight. [62] [63]
The smallest Mesozoic mammaliaform was Hadrocodium with a skull of 1.5 cm (0.59 in) in length and a body mass of 2 g (0.071 oz). [69]
The smallest marsupial is the long-tailed planigale from Australia. It has a body length of 110–130 millimetres (4.3–5.1 in) (including tail) and weighs 4.3 grams (0.15 oz) on average. The Pilbara ningaui is considered to be of similar size and weight. [70]
The Etruscan shrew (Suncus etruscus), is the smallest mammal by mass, weighing about 1.8 g (0.063 oz) on average. [71] The smallest mammal that ever lived, the shrew-like Batodonoides vanhouteni , weighed 1.3 grams (0.046 oz). [72]
The Kitti's hog-nosed bat (Craseonycteris thonglongyai), also known as the bumblebee bat, from Thailand and Myanmar [73] is the smallest mammal, at 29–33 millimetres (1.1–1.3 in) in length and 2 grams (0.071 oz) in weight. [74] [75]
The smallest member of the order Carnivora is the least weasel (Mustela nivalis), with an average body length of 114–260 mm (4.5–10.2 in). It weighs between 29.5–250 g (1.04–8.82 oz) with females being lighter.[ citation needed ]
The smallest known member of the rodent order is the Baluchistan pygmy jerboa, with an average body length of 3.8 cm (1.5 in). [70]
The smallest member of the primate order is Madame Berthe's mouse lemur (Microcebus berthae), found in Madagascar, [76] with an average body length of 9.2 cm (3.6 in).
The smallest cetacean, which is also (as of 2006) the most endangered, is the vaquita, a species of porpoise. Male vaquitas grow to an average of around 135 cm (53 in); the females are slightly longer, averaging about 141 cm (56 in) in length.[ citation needed ]
Zamia pygmaea is a cycad found in Cuba, and the smallest known gymnosperm. [77] It grows to a height of 25 cm (10 in). [78]
Duckweeds of the genus Wolffia are the smallest angiosperms. [79] Fully grown, they measure 300 by 600 μm (0.30 by 0.60 mm) and reach a mass of just 150 μg.
The smallest known dicotyledon plant is the Himalayan dwarf mistletoe (Arceuthobium minutissimum). Shoots grow up to 5 mm (0.20 in) in height. [80]
Nanobes are thought by some scientists to be the smallest known organisms, [81] 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, but it is unclear what they are, and if they are alive.[ citation needed ]
Mimivirus is a genus of giant viruses, in the family Mimiviridae. Amoeba serve as their natural hosts. This genus contains a single identified species named Acanthamoeba polyphaga mimivirus (APMV). It also refers to a group of phylogenetically related large viruses.
Potyviridae is a family of positive-strand RNA viruses that encompasses more than 30% of known plant viruses, many of which are of great agricultural significance. The family has 12 genera and 235 species, three of which are unassigned to a genus.
Genome size is the total amount of DNA contained within one copy of a single complete genome. It is typically measured in terms of mass in picograms or less frequently in daltons, or as the total number of nucleotide base pairs, usually in megabases. One picogram is equal to 978 megabases. In diploid organisms, genome size is often used interchangeably with the term C-value.
The Old World silversides are a family, Atherinidae, of fish in the order Atheriniformes. Atherinidae are abundant and considered bony fish (teleost) that are widespread globally, living in rivers, estuaries, and coastal waters. They occur worldwide in tropical and temperate waters. About two-thirds of the species are marine, and the remainder live in fresh water. The 74 species are in 13 genera. The genus Craterocephalus is the most diverse with 25 species. Four genera are monotypic.
Paedocypris is a genus of tiny cyprinid fish found in swamps and streams on the Southeast Asian islands of Borneo, Sumatra and Bintan.
Paedocypris progenetica, the dwarf goby, is a species of tiny cyprinid fish endemic to the Indonesian islands of Sumatra and Bintan where it is found in peat swamps and blackwater streams. It was discovered by Singaporean ichthyologist Heok Hui Tan. He has written a description of the fish along with another species of the same genus called Paedocypris micromegethes.
Quasipaa spinosa is a species of frog in the family Dicroglossidae. It is known under many common names, including Chinese spiny frog, giant spiny frog, Chinese edible frog, and spiny paa frog. Its names refer to the distinctive characteristics of the species, relatively large size and the spiny chest of male frogs. Giant in frog terms only, it can nevertheless grow to lengths above 10 cm (4 in); this makes it the largest frog in Hong Kong.
The western clawed frog is a species of frog in the family Pipidae, also known as tropical clawed frog. It is the only species in the genus Xenopus to have a diploid genome. Its genome has been sequenced, making it a significant model organism for genetics that complements the related species Xenopus laevis, a widely used vertebrate model for developmental biology. X. tropicalis also has a number of advantages over X. laevis in research, such as a much shorter generation time, smaller size, and a larger number of eggs per spawn.
Ultramicrobacteria are bacteria that are smaller than 0.1 μm3 under all growth conditions. This term was coined in 1981, describing cocci in seawater that were less than 0.3 μm in diameter. Ultramicrobacteria have also been recovered from soil and appear to be a mixture of Gram-positive, Gram-negative and cell-wall-lacking species. Ultramicrobacteria possess a relatively high surface-area-to-volume ratio due to their small size, which aids in growth under oligotrophic conditions. The relatively small size of ultramicrobacteria also enables parasitism of larger organisms; some ultramicrobacteria have been observed to be obligate or facultative parasites of various eukaryotes and prokaryotes. One factor allowing ultramicrobacteria to achieve their small size seems to be genome minimization such as in the case of the ultramicrobacterium P. ubique whose small 1.3 Mb genome is seemingly devoid of extraneous genetic elements like non-coding DNA, transposons, extrachromosomal elements etc. However, genomic data from ultramicrobacteria is lacking since the study of ultramicrobacteria, like many other prokaryotes, is hindered by difficulties in cultivating them.
This article lists the largest organisms for various types of life and mostly considers extant species, which found on Earth can be determined according to various aspects of an organism's size, such as: mass, volume, area, length, height, or even genome size. Some organisms group together to form a superorganism, but such are not classed as single large organisms. The Great Barrier Reef is the world's largest structure composed of living entities, stretching 2,000 km (1,200 mi) but contains many organisms of many types of species.
Picobirnavirus is a genus of double-stranded RNA viruses. It is the only genus in the family Picobirnaviridae. Although amniotes, especially mammals, were thought to serve as hosts, it has been recently suggested that these viruses might infect bacteria and possibly some other invertebrates. If they do infect bacteria, then they are Bacteriophages. There are three species in this genus. Associated symptoms include gastroenteritis in animals and humans, though the disease association is unclear.
Lymphocystivirus is a genus of viruses, in the family Iridoviridae. Fish serve as natural hosts. There are four species in this genus. Diseases associated with this genus include: tumor-like growths on the skin.
Megavirus is a viral genus containing a single identified species named Megavirus chilense, phylogenetically related to Acanthamoeba polyphaga Mimivirus (APMV). In colloquial speech, Megavirus chilensis is more commonly referred to as just “Megavirus”. Until the discovery of pandoraviruses in 2013, it had the largest capsid diameter of all known viruses, as well as the largest and most complex genome among all known viruses.
Paedophryne amauensis, also known as the New Guinea Amau frog, is a species of microhylid frog endemic to eastern Papua New Guinea. At 7.7 mm (0.30 in) in snout-to-vent length, it is considered the world's smallest known vertebrate.
The largest animal currently alive is the blue whale. The maximum recorded weight was 190 tonnes for a specimen measuring 27.6 metres (91 ft), whereas longer ones, up to 33 metres (108 ft), have been recorded but not weighed. It is estimated that this individual could have a mass of 250 tonnes or more. The longest non-colonial animal is the lion's mane jellyfish.
Pithovirus, first described in a 2014 paper, is a genus of giant virus known from two species, Pithovirus sibericum, which infects amoebas and Pithovirus massiliensis. It is a DNA based virus and is a member of the nucleocytoplasmic large DNA viruses clade. The 2014 discovery was made when a viable specimen was found in a 30,000-year-old ice core harvested from permafrost in Siberia, Russia.
Genomic streamlining is a theory in evolutionary biology and microbial ecology that suggests that there is a reproductive benefit to prokaryotes having a smaller genome size with less non-coding DNA and fewer non-essential genes. There is a lot of variation in prokaryotic genome size, with the smallest free-living cell's genome being roughly ten times smaller than the largest prokaryote. Two of the free-living bacterial taxa with the smallest genomes are Prochlorococcus and Pelagibacter ubique, both highly abundant marine bacteria commonly found in oligotrophic regions. Similar reduced genomes have been found in uncultured marine bacteria, suggesting that genomic streamlining is a common feature of bacterioplankton. This theory is typically used with reference to free-living organisms in oligotrophic environments.
Batravirus ranidallo1, also known as Ranid herpesvirus 1 (RaHV-1), is a double-stranded DNA virus within the order Herpesvirales. The virus was initially observed within renal tumors in 1934 by Baldwin Lucké, and more recently has become identifiable through the use of PCR in samples isolated from frog tumors. RaHV-1 causes renal tumors within the northern leopard frog, Rana pipiens. The virus has not yet been isolated in vitro within cell lines, meaning that while its existence and symptoms are fairly evident, its methods of transmission, cell infection, and reproduction are largely unknown.
Virosphere was coined to refer to all those places in which viruses are found or which are affected by viruses. However, more recently virosphere has also been used to refer to the pool of viruses that occurs in all hosts and all environments, as well as viruses associated with specific types of hosts, type of genome or ecological niche.