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.

Microorganisms

Viruses

The majority of 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 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. [http://www-iphicles.rcsb.org/pdb/lists/pdb-l/200012/msg00048.html]

The Porcine circovirus 2 is a single stranded DNA virus having a capsid diameter of 17 nm. [ [http://phene.cpmc.columbia.edu/ICTVdB/WWW/16002005.htm ICTVdB Virus Description - 00.016.0.01.005. Porcine circovirus 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 0.2 to 0.3 µm (micrometers), "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 0.22 µm ultrafilter. A complicating factor is nutrient-downsized bacteria, bacteria that become much smaller due to lack of available nutrients. [ [http://www.madsci.org/posts/archives/sep2001/1001464156.Gb.r.html Re: What is the smallest living thing? ] ]

mallest organisms in certain groups

mallest insect

Adult males of the parasitic wasp "Dicopomorpha echmepterygis" can be as small as 139 μm long; females are 40 percent larger. [ [http://ufbir.ifas.ufl.edu/chap38.htm University of Florida Book of Insect Records] ]

mallest 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. [cite journal
quotes = no
author = Polilov, A.A.
year = 2008
title = Anatomy of the Smallest Coleoptera, Featherwing Beetles of the Tribe Nanosellini (Coleoptera, Ptiliidae), and Limits of Insect Miniaturization
journal = Entomological Review
volume = 88 | issue = 1 | pages = 26–33]

mallest 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 [ [http://magma.nationalgeographic.com/ngexplorer/0403/articles/mainarticle.html National Geographic Explorer (Student Magazine) - Freaky Frogs ] ] .

mallest reptile

The Jaragua Sphaero (dwarf gecko) ("Sphaerodactylus ariasae"), a gecko in the "Sphaerodactylus" genus, is the world's smallest known reptile species, at 16 mm long. The species was first described in the December 2001 issue of the "Caribbean Journal of Science" by Pennsylvania State University evolutionary biologist Blair Hedges and University of Puerto Rico biologist Richard Thomas. The 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. [ [http://news.bbc.co.uk/1/hi/sci/tech/1689313.stm BBC News | SCI/TECH | Tiny gecko is 'world's smallest' ] ] The species's binomial name was in honor of Yvonne Arias, the leader of the Dominican environmental group Grupo Jaragua. [http://www.conservation.org/xp/news/press_releases/2001/120301.xml] [http://forests.org/archive/samerica/wosmliza.htm]

mallest bird

The bee hummingbird ("Mellisuga helenae") is the world's smallest known bird species and the smallest known 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. Said to be "more apt to be mistaken for a bee than a bird," the hummingbird's wings beat 80 times per second and up to 200 times when mating. [ [http://www.mschloe.com/hummer/carib.htm Hummingbirds of the Caribbean [mschloe.com ] ] 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.

mallest fish

The smallest known fish (and smallest known vertebrate) are part of the "Paedocypris" genus 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. [ [http://news.bbc.co.uk/1/hi/sci/tech/4645708.stm BBC NEWS | Science/Nature | Scientists find 'smallest fish' ] ] [ [http://www.amonline.net.au/fishes/faq/smallest.htm What is the smallest species of fish? ] ] [ [http://news.bbc.co.uk/2/hi/science/nature/4666736.stm BBC NEWS | Science/Nature | Smallest fish compete for honours ] ] [ [http://www.livescience.com/animalworld/041027_Smallest_Fish.html Bragging Rights: The Smallest Fish Ever | LiveScience ] ]

mallest mammal

The endangered Kitti's Hog-nosed Bat (bumblebee bat; "Craseonycteris thonglongyai") of Thailand 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. However, the Etruscan Shrew is the smallest mammal by mass, though it exceeds the Bumblebee Bat in skull size.

ee also

*Largest organism

References

External Links

* [http://creatures.ifas.ufl.edu/misc/beetles/featherwing_beetles.htm featherwing beetles] on the UF / IFAS Featured Creatures Web site