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Smallest organisms

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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.

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 elements such as satelliviruses, Viroids and Ribozymes.

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

Nanobes

File:Nanobe.gif
Nanobe
File:Nanobe2.gif
Nanobe

Nanobes are thought by some to be the smallest known organism, 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

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, bacteria that become much smaller due to a lack of available nutrients.[3]

Eukaryotes

Prasinophyte algae of the genus Ostreococcus are the smallest free-living eukaryote. The single cell of an Ostreococcus measures only 0.8 μm across.

Arthropods

Smallest arachnid

Eriophyid mites are among the smallest of all arthropods, measuring only 125 to 250 μm in length.[4]

Smallest insect

Adult males of the parasitic wasp Dicopomorpha echmepterygis can be as small as 139 μm long; females are 40 percent larger.[5]

  • 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.[6]

Smallest crustacean

The smallest crustacean, and indeed the smallest arthropod is the tantulocarid Stygotantulus stocki, at a length of only 94 μm (0.0037 in).[7]

Echinoderms

The smallest sea cucumber, and also smallest echinoderm is Psammothuria ganapatii, a synaptid which lives between sand grains on the coast of India. Its maximum length is only 4 mm.[8] [9]

Sea urchins

The smallest sea urchin, Echinocyamus scaber, has a test only 6 mm across.[9]

Starfish

Patiriella parvivipara is the smallest starfish, at only 5 mm across.[9]

Vertebrates

Paratype of Paedophryne amauensis (LSUMZ 95004) on a US dime.

The smallest vertebrates (and smallest amphibians) known are Paedophryne amauensis frogs from Papua New Guinea, which range in length from 7.0 to 8.0 mm, and average 7.7 mm.[10][11] Previously, the title of smallest vertebrate was held by members of the fish genus Paedocypris of Indonesia.

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.[12][13][14][15]

Smallest salamander

The average length of several specimens of the salamander Thorius arboreus was only 17 millimetres (0.67 in) .

Smallest reptile

The Jaragua Sphaero (Sphaerodactylus ariasae) and the Virgin Islands Dwarf Sphaero (S. parthenopion), two geckos in the genus Sphaerodactylus, are the world's smallest known reptile species and smallest lizard, with a snout-vent length of 16 millimetres (0.63 in).[16] 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.[17] 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 the Dominican Republic.[18][19]

Smallest turtle

The world's 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).[20]

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 (5.2 ft) in length.[21]

Smallest snake

One of the smallest snakes known is the recently discovered Barbados Threadsnake (Leptotyphlops carlae). Adults average about 10 cm long, which is only about twice as long as the hatchlings.

Smallest non-avian dinosaur

The smallest known 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).[22] Nevertheless, sizes of dinosaurs are commonly labelled with a level of uncertainty, as the available material often (or even usually) is incomplete.

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 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".[23] 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.

Smallest mammal

The vulnerable Kitti's Hog-nosed Bat (bumblebee bat; Craseonycteris thonglongyai) from Thailand and Myanmar[24] is the smallest mammal, at 30–40 mm in length and 1.5 to 2 g in weight.

The Etruscan Shrew is the smallest mammal by mass, though it exceeds the Bumblebee Bat in skull size. The smallest mammal that ever lived, the shrew-like Batodonoides vanhouteni, weighed only 1.3 g.

Smallest primate

The smallest member of the primate order is Madame Berthe's Mouse Lemur (Microcebus berthae), found in Madagascar, [25] with an average body length of 92 mm (3.6 in).

Plants

Smallest angiosperms

Duckweeds of the genus Wolffia are the world's smallest flowering plants.[26] Fully grown, they measure only 300 µm by 600 µm and reach a mass of just 150 µg.

See also

References

  1. ^ http://www-iphicles.rcsb.org/pdb/lists/pdb-l/200012/msg00048.html
  2. ^ ICTVdB Virus Description - 00.016.0.01.005. Porcine circovirus 2
  3. ^ Re: What is the smallest living thing?
  4. ^ Mohanasudaram, M. (1987). "Studies on the genus Aceria (Acari, Eriophyidae) from South India" (PDF). Journal of Acarology. 12 (1 & 2). Acarological Society of India: 15–88.
  5. ^ University of Florida Book of Insect Records
  6. ^ Polilov, A.A. (2008). "Anatomy of the Smallest Coleoptera, Featherwing Beetles of the Tribe Nanosellini (Coleoptera, Ptiliidae), and Limits of Insect Miniaturization". Entomological Review. 88 (1): 26–33. doi:10.1134/S0013873808010041.
  7. ^ Joel W. Martin & George E. Davis (2001). An Updated Classification of the Recent Crustacea (PDF). Natural History Museum of Los Angeles County. pp. 132 pp.
  8. ^ Rao, G. Chandrasekhara (1968). "On Psammothuria ganapatii n. gen. n. sp., an interstitial holothurian from the beach sands of waltair coast and its autecology". Proceedings: Plant Sciences. 67 (5): 201–206. doi:10.1007/BF03053902.
  9. ^ a b c Gilpin, Daniel (2006). Starfish, urchins, and other echinoderms. London: David West Children's Books. p. 41. ISBN 0-7565-1611-0Template:Inconsistent citations{{cite book}}: CS1 maint: postscript (link)
  10. ^ "World's tiniest frogs found in Papua New Guinea". The Australian. 12 January 2012. Retrieved 11 January 2012.
  11. ^ Rittmeyer, Eric N.; Allison, Allen; Gründler, Michael C.; Thompson, Derrick K.; Austin, Christopher C. (2012). "Ecological guild evolution and the discovery of the world's smallest vertebrate". PLoS ONE. 7 (1). doi:doi:10.1371/journal.pone.0029797. Retrieved 11 January 2012. {{cite journal}}: Check |doi= value (help)
  12. ^ "Scientists find 'smallest fish'". BBC News. 2006-01-25. Retrieved 2010-05-23.
  13. ^ What is the smallest species of fish?
  14. ^ "Smallest fish compete for honours". BBC News. 2006-01-31. Retrieved 2010-05-23.
  15. ^ Bragging Rights: The Smallest Fish Ever | LiveScience
  16. ^ Pennsylvania State University (2001). World's Smallest Lizard Discovered in the Caribbean. Accessed 26 January 2009.
  17. ^ Glaw, F., & Vences, M. (2007). A Field Guide to the Amphibians and Reptiles of Madagascar, 3d edition. Frosch Verlag. ISBN 9783929449037
  18. ^ "Tiny gecko is 'world's smallest'". BBC News. 2001-12-03. Retrieved 2010-05-23.
  19. ^ [1]
  20. ^ Branch, B. (1998). Field Guide to Snakes and other Reptiles of Southern Africa. 3d edition. Struik Publishers. ISBN 1 86872 040 3
  21. ^ CROCODILIANS Natural History & Conservation. Paleosuchus palpebrosus.
  22. ^ Xu, X., Zhao, Q., Norell, M., Sullivan, C., Hone, D., Erickson, G., Wang, X., Han, F. and Guo, Y. (2009). "A new feathered maniraptoran dinosaur fossil that fills a morphological gap in avian origin." Chinese Science Bulletin, 6 pages, accepted November 15, 2008.
  23. ^ Hummingbirds of the Caribbean [mschloe.com]
  24. ^ Template:IUCN2008 Listed as Vulnerable
  25. ^ http://www.primates.co.uk/lemurs/pygmy-mouselemur.html (Retrieved on March 17, 2010).
  26. ^ What is the smallest flower in the world?
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