Smallest organisms

The smallest organism found on Earth can be measured using a variety of different methods, and can be defined as the smallest by volume, mass, height, or length. Because there is some dispute over what the definition of life is and what entities qualify as organisms, the actual "smallest organism" (microorganisms) may be unclear. A further complication is the incomplete nature of scientific knowledge: it is possible that the smallest organism has yet to be discovered.

Contents 1 Microorganisms 1.1 Viruses 1.2 Nanobes 1.3 Nanoarchaeum 1.4 Mycoplasma genitalium 2 Arthropods 2.1 Smallest insect 3 Vertebrates 3.1 Smallest amphibian 3.2 Smallest reptile 3.2.1 Smallest turtle 3.2.2 Smallest crocodilian 3.3 Smallest bird 3.3.1 Dinosaur 3.4 Smallest mammal 4 Plants 4.1 Smallest angiosperms 5 See also 6 References 7 External links

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 synthesise 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. The smallest RNA viruses in terms of genome size are small retroviruses such as rous sarcoma virus with genomes of 3.5 kb and particle diameters of 80 nm. The smallest 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. The smallest DNA bacteriophage is the Phi-X174 phage, thought to be larger than Hepatitis B, at about 4 kb. ^[1]. It is important to consider other self replicating genetic elmenets such as satelliviruses, Viroids and Ribozymes.

The Porcine circovirus 2 is a single stranded DNA virus having a capsid diameter of 17 nm.^[2]

Nanobes

Nanobes are thought by some to be the smallest known organism, about one tenth the size of the smallest known bacteria. Nobes, tiny filamental structures first found in some rocks and sediments, were first described in 1996 by Philipa Uwins of the University of Queensland. The smallest are 20 nm long. Some researchers believe them to be merely crystal growths, but a purported find of DNA in nanobe samples may prove otherwise. They are similar to the life-like structures found in ALH84001, the famous Mars meteorite from the Antarctic.

Nanoarchaeum

Nanoarchaeum equitans is a species of tiny microbe 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. Its cells are only 400 nm in diameter, making it the smallest known living organism, with the possible exception of nanobes (if they are considered to be living). Its genome is only 490,885 nucleotides long; as of 2005 it remains the smallest non-viral genome ever sequenced.

Mycoplasma genitalium

Mycoplasma genitalium, a parasitic bacterium which lives in the primate 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 ultramicrobacteria Sphingomonas sp strain RB2256 is reported to have passed through 220 nm ultrafilter. A complicating factor is nutrient-downsized bacteria, a bacteria that become much smaller due to a lack of available nutrients. ^[3]

Arthropods

Smallest insect

Adult males of the parasitic wasp Dicopomorpha echmepterygis can be as small as 139 μm long; females are 40 percent larger. ^[4]

• Smallest beetle

Beetles of the tribe Nanosellini are all less than 1 mm long; the smallest include Scydosella musawasensis at 300 μm long, Vitusella fijiensis at 310 μm, and Nanosella at 300 to 400 μm. These are among the tiniest non-parasitic insects. ^[5]

Vertebrates

The smallest vertebrates (and smallest fishes) known are part of the genus Paedocypris of Indonesia, which dwell in peat swamps and can survive extreme drought in part due to their small size (just 7.9 mm long at maturity). Much of their habitat is acid water, with pH as low as 2.9. The members of the genus are thought to be highly endangered.

Male individuals of the species anglerfish Photocorynus spiniceps have been documented to be 6.2-7.3 mm 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 50.5 mm. ^[6][7][8][9]

Smallest amphibian

At 9.6 to 9.8 millimeters long, the Monte Iberia Eleuth (Eleutherodactylus iberia) and the Brazilian Gold Frog (Brachycephalus didactylus) are tied as the smallest frog, amphibian, or tetrapod.^[10]

Smallest reptile

The Jaragua Sphaero (Sphaerodactylus ariasae) and the Virgin Gorda Least Gecko (S. parthenopion), two geckos in the genus Sphaerodactylus, are the world's smallest known reptile species, with a snout-vent length of 16 mm.^[11] A few Brookesia chameleons from Madagascar may be equally small, with a reported snout-vent length of 15-18 mm. for male B. minima, and 14-19 mm. for male B. tuberculata, though females are larger.^[12] Of the aforementioned geckos, S. ariasae was first described in 2001 by biologists Blair Hedges and Richard Thomas. This dwarf gecko is endangered and lives in Jaragua National Park in the Dominican Republic and on Beata Island (Isla Beata), off the southern coast of Hispaniola in Haiti.^[13][14]

Smallest turtle

The world's smallest turtle is the Speckled Padloper Tortoise (Homopus signatus) from South Africa. The males measure 6-8 cm (2.3-3.1 in), while females measure up to almost 10 cm (4 in).^[15]

Smallest crocodilian

The smallest crocodilian is the Cuvier's Dwarf Caiman (Paleosuchus palpebrosus) from northern and central South America. It reaches up to 1.6 m (5 ft) in length.^[16]

Smallest bird

With a mass of approximately 1.8 grams (0.063 oz) and a length of 5 centimetres (2.0 in), the Bee Hummingbird (Mellisuga helenae) is the world's smallest bird species and the smallest warm-blooded vertebrate.

M. helenae, called the zunzún in its native habitat on Cuba and the Isle of Youth, has a mass of about 1.8 g, which is lighter than a Canadian or U.S. penny. It is said to be "more apt to be mistaken for a bee than a bird".^[17] The Bee Hummingbird is said to eat half its total body mass and drink eight times its total body mass each day. Its nest is 3 cm across.

Dinosaur

The smallest known non-avian dinosaur is Microraptor, a genus of feathered dinosaurs that lived in what is now China during the early Cretaceous Period 130-125.5 million years ago. Adult specimens range from 42–83 cm (1.4–2.7 ft) long, and the weight has been estimated at up to 1 kg (2.2 lbs). Nevertheless, sizes of dinosaurs are commonly labelled with a level of uncertainty, as the available material often (or even usually) is incomplete.

Smallest mammal

The vulnerable Kitti's Hog-nosed Bat (bumblebee bat; Craseonycteris thonglongyai) from Thailand and Myanmar^[18] is the smallest mammal, at 30-40 mm in length and 1.5 to 2 g in weight, about the weight of a Canadian or U.S. dime.

The Etruscan Shrew is the smallest mammal by mass, though it exceeds the Bumblebee Bat in skull size.

Plants

Smallest angiosperms

Duckweeds of the genus Wolffia are the worlds smallest flowering plants.^[19] Fully grown, they measure only 300 µm by 600 µm and reach a mass of just 150 µg.

See also

• Largest organism

References

External links

• featherwing beetles on the UF / IFAS Featured Creatures Web site