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Encyclopedia > Tardigrade
Tardigrade
Fossil range: Early Cambrian to Recent[1]
The tardigrade Hypsibius dujardini
The tardigrade Hypsibius dujardini
Scientific classification
Kingdom: Animalia
Subkingdom: Ecdysozoa
(unranked) Panarthropoda
Phylum: Tardigrada
Spallanzani, 1777
Classes [2]

Heterotardigrada
Mesotardigrada
Eutardigrada For other uses, see Cambrian (disambiguation). ... Image File history File links Metadata No higher resolution available. ... Scientific classification redirects here. ... For other uses, see Animal (disambiguation). ... Phyla Scalidophora (288 species)   Priapulida (16 species)   Kinorhyncha (150 species)   Loricifera (122 species) Nematoda (20,000+ species) Nematomorpha (320 species) Panarthropoda (6,181,000-10,193,000+ species)   Onychophora (200 species)   Tardigrada (1,000+ species)   Arthropoda (6,180,000-10,192,000+ species) The Ecdysozoa are a group of protostome... Panarthropoda is a taxon combining the Phyla Arthropoda, Tardigrada and Onychophora. ... Lazzaro Spallanzani. ... Families Order Arthrotardigrada     Archechiniscidae     Batillipedidae     Coronarctidae     Halechiniscidae     Renaudarctidae     Stygarctidae Order Echiniscoidea     Echiniscidae     Echiniscoididae     Oreellidae The class Heterotardigrada includes tardigrades (water bears) that have cephalic appendages and legs with four separate but similar digits and/or claws on each. ... Family Thermozodiidae The class Mesotardigrada has only one species, Thermozodium esakii. ... Families Order Apochaela     Milnesiidae Order Parachaela     Macrobiotidae     Microhypsibiidae     Calohypsibiidae     Hypsibiidae Eutardigrada are tardigrada without lateral appendices. ...

Tardigrades (commonly known as water bears) comprise the phylum Tardigrada. They are small, segmented animals, similar and probably related to the arthropods. Tardigrades were first described by Johann August Ephraim Goeze in 1773 (kleiner Wasserbär = little water bear). The name Tardigrada means "slow walker" and was given by Spallanzani in 1777. The biggest adults may reach a body length of 1.5 mm, the smallest below 0.1 mm. Freshly hatched larvae may be smaller than 0.05 mm. For other uses, see phyla. ... For other uses, see Animal (disambiguation). ... Subphyla and Classes Subphylum Trilobitomorpha Trilobita - trilobites (extinct) Subphylum Chelicerata Arachnida - spiders,scorpions, etc. ... Johann August Ephraim Goeze (28 May 1731 - 27 June 1793) was a German zoologist. ... Year 1773 (MDCCLXXIII) was a common year starting on Friday (link will display the full calendar) of the Gregorian calendar (or a common year starting on Tuesday of the 11-day slower Julian calendar). ... Lazzaro Spallanzani. ... Year 1777 (MDCCLXXVII) was a common year starting on Wednesday (link will display the full calendar) of the Gregorian calendar (or a common year starting on Sunday of the 11-day slower Julian calendar). ... A millimetre (American spelling: millimeter, symbol mm) is an SI unit of length that is equal to one thousandth of a metre. ... A larval insect A larva (Latin; plural larvae) is a juvenile form of animal with indirect development, undergoing metamorphosis (for example, insects or amphibians). ...


More than 1000 species of tardigrades have been described. Tardigrades occur over the entire world, from the high Himalayas (above 6,000 m), to the deep sea (below 4,000 m) and from the polar regions to the equator. For the movie Himalaya, see Himalaya (film). ... This article is about the unit of length. ... For the IMAX movie, see Deep Sea 3D. A hydrothermal vent in the deep sea The deep sea, or deep layer[1] is the lowest layer in the ocean, existing below the thermocline. ... Location of the polar regions Northern Hemisphere permafrost (permanently frozen ground) in purple. ... World map showing the equator in red In tourist areas, the equator is often marked on the sides of roads The equator marked as it crosses Ilhéu das Rolas, in São Tomé and Príncipe. ...


The most convenient place to find tardigrades is on lichens and mosses. Other environments are dunes, beaches, soil and marine or freshwater sediments, where they may occur quite frequently (up to 25,000 animals per litre). Tardigrades often can be found by soaking a piece of moss in spring water.[3] For other uses, see Lichen (disambiguation). ... For other uses, see Moss (disambiguation). ... This article is about sand formations. ... For other uses, see Beach (disambiguation). ... Loess field in Germany Surface-water-gley developed in glacial till, Northern Ireland For the American hard rock band, see SOiL. For the System of a Down song, see Soil (song). ... Animated map exhibiting the worlds oceanic waters. ... Fresh water redirects here. ... The litre or liter (see spelling differences) is a unit of volume. ... For other uses, see Moss (disambiguation). ...


Water bears are able to survive in extreme environments that would kill almost any other animal. They can survive temperatures close to absolute zero[4], temperatures as high as 151°C (303°F), 1,000 times more radiation than any other animal[5], nearly a decade without water, and can also survive in a vacuum like that found in space.

Contents

Anatomy and morphology

Tardigrades have a body with four segments (not counting the head), four pairs of legs without joints, and feet with claws or toes. The cuticle contains chitin and is moulted. They have a ventral nervous system with one ganglion per segment, and a multilobed brain. Instead of a coelom they have a haemocoel. The only place where a true coelom can be found is around the gonad (coelomic pouch). The pharynx is of a triradiate, muscular, sucking kind, armed with stylets. Although some species are parthenogenetic, males and females are usually present, each with a single gonad. Tardigrades are eutelic (all adult tardigrades of the same species are believed to have the same number of cells) and oviparous. Some tardigrade species have as many as about 40,000 cells in each adult's body, others have far fewer. [6][7] Morphogenesis (from the Greek morphê shape and genesis creation) is one of three fundamental aspects of developmental biology along with the control of cell growth and cellular differentiation. ... Cat claw A claw is a curved pointed appendage, found at the end of a toe or finger or, in arthropods, of the tarsus. ... This article is about the body part. ... Eponychium is the anatomical term for the human cuticle In biology, the term cuticle or cuticula is given to to a variety of tough but flexible, non-mineral outer coverings of an organism, or part of an organism, that provide prtoection. ... Structure of the chitin molecule, showing two of the N-Acetylglucosamine units that repeat to form long chains in beta-1,4 linkage. ... Ecdysis is the molting of the cuticula in arthropods and related groups (Ecdysozoa). ... The ventral nerve cords make up the nervous system of arthropods. ... This is a dorsal root ganglion (DRG) from a chicken embryo (around stage of day 7) after incubation overnight in NGF growth medium stained with anti-neurofilament antibody. ... For other uses, see Brain (disambiguation). ... Coelom with Dermal Tissue One of the primary ways zoologists group animals has to do with the presence or absence of a coelom and how it is formed. ... A Hemocoel is a cavity or series of spaces between the organs of organisms with open circulatory systems like most arthropods and mollusks. ... The pharynx (plural: pharynges) is the part of the neck and throat situated immediately posterior to the mouth and nasal cavity, and cranial, or superior, to the esophagus, larynx, and trachea. ... The stylet or stomatostyle, is the primitive mouth-parts of the nematode. ... For the religious belief, see Virgin Birth of Jesus. ... The gonad is the organ that makes gametes. ... Eutelic means that there are a fixed number of cells in an adult body of an organism of a single species. ...


Ecology and life history

Feeding ecology

Most tardigrades are phytophagous or bacteriophagous, but some are predatory[8] (e.g. Milnesium tardigradum).[9] Phagy or phagia is an ecological term that is used to identify particular nutritional systems. ... This snapping turtle is trying to make a meal of a Canada goose, but the goose is too wary. ...


Physiology

Extreme environments

Tardigrades are very hardy animals; scientists have reported their existence in hot springs, on top of the Himalayas, under layers of solid ice and in ocean sediments. Many species can be found in a milder environment like lakes, ponds and meadows, while others can be found in stone walls and roofs. Tardigrades are most common in moist environments, but can stay active wherever they can retain at least some moisture. Green Dragon Spring at Norris Geyser A hot spring is a place where warm or hot groundwater issues from the ground on a regular basis for at least a predictable part of the year, and is significantly above the ambient ground temperature (which is usually around 55~57 F or... For the movie Himalaya, see Himalaya (film). ... This article is about water ice. ... For other uses, see Lake (disambiguation). ... Two people reflected in a fish pond A pond is typically a man made body of water smaller than a lake. ... A meadow is a habitat of rolling or flat terrain where grasses predominate. ...


Tardigrades are one of the few groups of species that are capable of reversibly suspending their metabolism and going into a state of cryptobiosis. Several species regularly survive in a dehydrated state for nearly ten years. Depending on the environment they may enter this state via anhydrobiosis, cryobiosis, osmobiosis or anoxybiosis. While in this state their metabolism lowers to less than 0.01% of what is normal and their water content can drop to 1% of normal. Their ability to remain desiccated for such a long period is largely dependent on the high levels of the non-reducing sugar trehalose, which protects their membranes. Structure of the coenzyme adenosine triphosphate, a central intermediate in energy metabolism. ... Cryptobiosis is an ametabolic state of life entered by some lower organisms in response to adverse environmental conditions such as desiccation, freezing, and oxygen deficiency. ... Cryptobiosis is an ametabolic state of life entered by some lower organisms in response to adverse environmental conditions such as desiccation, freezing, and oxygen deficiency. ... This article is about sugar as food and as an important and widely-traded commodity. ... Trehalose, also known as mycose, is a type of alpha-linked disaccharide formed by an α, α-1, 1-glucoside bond between α-glucose units found extensively but not abundantly in nature. ... Look up cell membrane in Wiktionary, the free dictionary. ...


Tardigrades have been known to withstand the following extremes while in this state:

  • Temperature — tardigrades can survive being heated for a few minutes to 151°C or being chilled for days at -200°C, or for a few minutes at -272°C. (1° warmer than absolute zero).[10]
  • Pressure — they can withstand the extremely low pressure of a vacuum and also very high pressures, many times greater than atmospheric pressure. It has recently been proven that they can survive in the vacuum of space. Recent research has notched up another feat of endurability; apparently they can withstand 6,000 atmospheres pressure, which is nearly six times the pressure of water in the deepest ocean trench. [11]
  • Dehydration - tardigrades have been shown to survive nearly one decade in a dry state.[12] Another researcher reported that a tardigrade survived over a period of 120 years in a dehydrated state, but soon died after 2 to 3 minutes.[13] Subsequent research has cast doubt on its accuracy since it was only a small movement in the leg.[14]
  • Radiation — as shown by Raul M. May from the University of Paris, tardigrades can withstand 5,700 grays or 570,000 rads of x-ray radiation. (Ten to twenty grays or 1,000–2,000 rads could be fatal to a human). The only explanation thus far for this ability is that their lowered hydration state provides fewer reactants for the ionizing radiation.

Recent experiments conducted by Cai and Zabder have also shown that these water bears can undergo chemobiosis — a cryptobiotic response to high levels of environmental toxins. However, their results have yet to be verified.[15][16] For other uses, see Temperature (disambiguation). ... For other uses, see Absolute Zero (disambiguation). ... This article is about pressure in the physical sciences. ... Look up Vacuum in Wiktionary, the free dictionary. ... Atmospheric pressure is the pressure at any given point in the Earths atmosphere. ... Dehydration (hypohydration) is the removal of water (hydro in ancient Greek) from an object. ... For other uses, see Radiation (disambiguation). ... The gray (symbol: Gy) is the SI unit of absorbed dose. ... The rad is a unit of radiation dose, with symbol rad. ... An X-ray picture (radiograph), taken by Wilhelm Röntgen in 1896, of his wife, Anna Bertha Ludwigs[1] hand X-rays (or Röntgen rays) are a form of electromagnetic radiation with a wavelength in the range of 10 to 0. ...


Evolutionary relationships and history

Recent DNA and RNA sequencing data indicate that tardigrades are the sister group to the arthropods and Onychophora. These groups have been traditionally thought of as close relatives of the annelids, but newer schemes consider them Ecdysozoa, together with the roundworms (Nematoda) and several smaller phyla. The Ecdysozoa-concept resolves the problem of the nematode-like pharynx as well as some data from 18S-rRNA and HOX (homeobox) gene data, which indicate a relation to roundworms. The structure of part of a DNA double helix Deoxyribonucleic acid, or DNA, is a nucleic acid molecule that contains the genetic instructions used in the development and functioning of all known living organisms. ... For other uses, see RNA (disambiguation). ... Subphyla and Classes Subphylum Trilobitomorpha Trilobita - trilobites (extinct) Subphylum Chelicerata Arachnida - spiders,scorpions, etc. ... Global range of Onychophora: Peripatidae in green, Peripatopsidae in blue Extant families Peripatidae Peripatopsidae Onychophora, the velvet worms (occasionally called walking worms or spitting worms), are segmented, caterpillar-like, terrestrial animals somewhat resembling both arthropods and annelid worms. ... For the characters from System Shock 2, see The Many. ... Phyla Scalidophora (288 species)   Priapulida (16 species)   Kinorhyncha (150 species)   Loricifera (122 species) Nematoda (20,000+ species) Nematomorpha (320 species) Panarthropoda (6,181,000-10,193,000+ species)   Onychophora (200 species)   Tardigrada (1,000+ species)   Arthropoda (6,180,000-10,192,000+ species) The Ecdysozoa are a group of protostome... Classes Adenophorea    Subclass Enoplia    Subclass Chromadoria Secernentea    Subclass Rhabditia    Subclass Spiruria    Subclass Diplogasteria The roundworms or nematodes (Phylum Nematoda from Gr. ... Phyla Scalidophora (288 species)   Priapulida (16 species)   Kinorhyncha (150 species)   Loricifera (122 species) Nematoda (20,000+ species) Nematomorpha (320 species) Panarthropoda (6,181,000-10,193,000+ species)   Onychophora (200 species)   Tardigrada (1,000+ species)   Arthropoda (6,180,000-10,192,000+ species) The Ecdysozoa are a group of protostome... The pharynx (plural: pharynges) is the part of the neck and throat situated immediately posterior to the mouth and nasal cavity, and cranial, or superior, to the esophagus, larynx, and trachea. ... A non-coding RNA (ncRNA) is any RNA molecule that functions without being translated into a protein. ... A homeobox is a stretch of DNA sequence found in genes involved in the regulation of the development (morphogenesis) of animals, fungi and plants. ... A homeobox is a DNA sequence found within genes that are involved in the regulation of development (morphogenesis) of animals, fungi and plants. ...


The minute sizes of tardigrades and their membranous integuments make their fossilization both difficult to detect and highly unlikely. The only known fossil specimens comprise some from mid-Cambrian deposits in Siberia and a few rare specimens from Cretaceous amber.[17] A fossil Ammonite Fossils (from Latin fossus, literally having been dug up) are the mineralized or otherwise preserved remains or traces (such as footprints) of animals, plants, and other organisms. ... For other uses, see Cambrian (disambiguation). ... This article is about Siberia as a whole. ... // The Cretaceous Period (pronounced ) is one of the major divisions of the geologic timescale, reaching from the end of the Jurassic Period (i. ... For other uses, see Amber (disambiguation). ...


The Siberian tardigrades differ from living tardigrades in several ways. They have three pairs of legs rather than four; they have a simplified head morphology; and they have no posterior head appendages. It is considered that they probably represent a stem group of living tardigrades.[17]


The rare specimens in Cretaceous amber comprise Milnesium swolenskyi, from New Jersey, the oldest, whose claws and mouthparts are indistinguishable from the living M. tartigradum; and two specimens from western Canada, some 15–20 million years younger than M. swolenskyi. Of the two latter, one has been given its own genus and family, Beorn leggi (the genus named by Cooper after the character Beorn from The Hobbit by J. R. R. Tolkien and the species named after his student William M. Legg), however it bears a strong resemblance to many living specimens in the family Hipsiblidae.[17][18] This article is about the U.S. state. ... In J. R. R. Tolkiens Middle-earth legendarium, Beorn was a shape-shifter, a man who could assume the appearance of a great black bear. ... For other uses, see Hobbit (disambiguation) and There and Back Again (disambiguation). ... Tolkien redirects here. ...


Aysheaia from the middle Cambrian Burgess shale might be related to tardigrades. Aysheaia pedunculata is a soft-bodied, caterpillar-shaped organism average body length of 1-6 cm. ... For other uses, see Cambrian (disambiguation). ... Hallucigenia sparsa, one of the organisms unique to the Burgess Shale. ...


References

  1. ^ Budd, G.E. (2001). "Tardigrades as ‘stem-group arthropods’: the evidence from the Cambrian fauna". Zool. Anz 240: 265-279. doi:10.1078/0044-5231-00034. 
  2. ^ Tardigrada (TSN 155166). Integrated Taxonomic Information System.
  3. ^ Goldstein, B. and Blaxter, M. (2002). Quick Guide: Tardigrades. Current Biology 12: R475. 
  4. ^ Bertolani, R. et al (2004). Experiences with dormancy in tardigrades. Journal of Limnology 63(Suppl 1): 16-25. 
  5. ^ Radiation tolerance in the tardigrade Milnesium tardigradum
  6. ^ Seki, K & Toyoshima, M. (1998). Preserving tardigrades under pressure. Nature 395: 853–854.
  7. ^ Ian M. Kinchin (1994) The Biology of Tardigrades, Ashgate Publishing
  8. ^ Lindahl, K. (2008-03-15). Tardigrade Facts.
  9. ^ Morgan, Clive I. (1977). "Population Dynamics of two Species of Tardigrada, Macrobiotus hufelandii (Schultze) and Echiniscus (Echiniscus) testudo (Doyere), in Roof Moss from Swansea". The Journal of Animal Ecology 46 (1): 263-279. 
  10. ^ Ramel, G. (2005-11-11). The Water Bears (Phylum Tardigrada).
  11. ^ Seki, K & Toyoshima, M. (1998). Preserving tardigrades under pressure. Nature 395: 853–854. 
  12. ^ Guidetti, R. & Jönsson, K.I. (2002). Long-term anhydrobiotic survival in semi-terrestrial micrometazoans. Journal of Zoology 257: 181-187. 
  13. ^ Manga Science Volume VI by Yoshitoh Asari, ISBN-05-202039-1, 1998
  14. ^ Guidetti, R. & Jönsson, K.I. (2002). Long-term anhydrobiotic survival in semi-terrestrial micrometazoans. Journal of Zoology 257. 
  15. ^ Franceschi, T. (1948). Anabiosi nei tardigradi. Bolletino dei Musei e degli Istituti Biologici dell'Università di Genova 22: 47–49. 
  16. ^ Jönsson, K. I. & R. Bertolani (2001). Facts and fiction about long-term survival in tardigrades. Journal of Zoology 255: 121–123. 
  17. ^ a b c David A. Grimaldi and Michael S. Engel (2005). Evolution of the Insects. Cambridge University Press, 96–97. ISBN 0521821495. 
  18. ^ Kenneth W. Cooper (1964). "The first fossil tardigrade: Beorn leggi, from Cretaceous Amber". Psyche – Journal of Entomology 71 (2): 41. 

A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... The Integrated Taxonomic Information System (ITIS) is a partnership designed to provide consistent and reliable information on the taxonomy of biological species. ... 2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Anno Domini (or common era), in accordance to the Gregorian calendar. ... is the 74th day of the year (75th in leap years) in the Gregorian calendar. ... Year 2005 (MMV) was a common year starting on Saturday (link displays full calendar) of the Gregorian calendar. ... is the 315th day of the year (316th in leap years) in the Gregorian calendar. ... This article is about the physical universe. ... The Journal of Zoology (not to be confused with a different journal called Zoology) is a scientific journal concerning zoology, the study of animals. ... The Journal of Zoology (not to be confused with a different journal called Zoology) is a scientific journal concerning zoology, the study of animals. ... The Journal of Zoology (not to be confused with a different journal called Zoology) is a scientific journal concerning zoology, the study of animals. ...

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Tardigrade - Wikipedia, the free encyclopedia (687 words)
Tardigrades occur over the whole world, from the high Himalaya (above 6000 m) to the deep sea (below 4000 m) and from the polar regions to the equator.
Tardigrades are very hardy animals; scientists have reported their existence in hot springs, on top of the Himalayas, under layers of solid ice and in ocean sediments.
Tardigrades are one of the few groups of species that are capable of reversibly suspending their metabolism and going into a state of cryptobiosis.
Tardigrade - definition of Tardigrade in Encyclopedia (519 words)
Tardigrades (Tardigrada), or "water bears", are a phylum of small, segmented animals, similar and related to the Arthropods.
Tardigrades have been found in so many different and varied environments that it is believed that they can be found virtually anywhere.
Tardigrades are one of the few species that are capable of reversibly suspending their metabolism and going into a state of cryptobiosis.
  More results at FactBites »

 
 

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