Tardigrades (), known colloquially as water bears or moss piglets,
are a
phylum
In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below kingdom and above class. Traditionally, in botany the term division has been used instead of phylum, although the International Code of Nomenclature ...
of eight-legged
segmented micro-animals.
They were first described by the German zoologist
Johann August Ephraim Goeze in 1773, who called them Kleiner Wasserbär ("little water bear"). In 1777, the Italian biologist
Lazzaro Spallanzani named them Tardigrada (), which means "slow steppers".
They have been found in diverse regions of Earth's
biosphere
The biosphere (from Greek βίος ''bíos'' "life" and σφαῖρα ''sphaira'' "sphere"), also known as the ecosphere (from Greek οἶκος ''oîkos'' "environment" and σφαῖρα), is the worldwide sum of all ecosystems. It can also ...
mountaintops, the
deep sea,
tropical rainforest
Tropical rainforests are rainforests that occur in areas of tropical rainforest climate in which there is no dry season – all months have an average precipitation of at least 60 mm – and may also be referred to as ''lowland equator ...
s, and the
Antarctic
The Antarctic ( or , American English also or ; commonly ) is a polar region around Earth's South Pole, opposite the Arctic region around the North Pole. The Antarctic comprises the continent of Antarctica, the Kerguelen Plateau and othe ...
.
Tardigrades are among the most resilient animals known,
with individual species able to survive extreme conditions – such as exposure to extreme temperatures, extreme
pressures (both high and low), air deprivation,
radiation
In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes:
* ''electromagnetic radiation'', such as radio waves, microwaves, infrared, visi ...
,
dehydration
In physiology, dehydration is a lack of total body water, with an accompanying disruption of metabolic processes. It occurs when free water loss exceeds free water intake, usually due to exercise, disease, or high environmental temperature. Mil ...
, and
starvation
Starvation is a severe deficiency in caloric energy intake, below the level needed to maintain an organism's life. It is the most extreme form of malnutrition. In humans, prolonged starvation can cause permanent organ damage and eventually, de ...
– that would quickly kill most other known forms of
life
Life is a quality that distinguishes matter that has biological processes, such as signaling and self-sustaining processes, from that which does not, and is defined by the capacity for growth, reaction to stimuli, metabolism, energy ...
. Tardigrades have survived exposure to
outer space
Outer space, commonly shortened to space, is the expanse that exists beyond Earth and its atmosphere and between celestial bodies. Outer space is not completely empty—it is a near-perfect vacuum containing a low density of particles, pred ...
. There are about 1,300 known species in the
phylum
In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below kingdom and above class. Traditionally, in botany the term division has been used instead of phylum, although the International Code of Nomenclature ...
Tardigrada, a part of the superphylum
Ecdysozoa
Ecdysozoa () is a group of protostome animals, including Arthropoda ( insects, chelicerata, crustaceans, and myriapods), Nematoda, and several smaller phyla. They were first defined by Aguinaldo ''et al.'' in 1997, based mainly on phylogenetic ...
consisting of animals that grow by
ecdysis
Ecdysis is the moulting of the cuticle in many invertebrates of the clade Ecdysozoa. Since the cuticle of these animals typically forms a largely inelastic exoskeleton, it is shed during growth and a new, larger covering is formed. The remnan ...
such as
arthropod
Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chiti ...
s and
nematode
The nematodes ( or grc-gre, Νηματώδη; la, Nematoda) or roundworms constitute the phylum Nematoda (also called Nemathelminthes), with plant- parasitic nematodes also known as eelworms. They are a diverse animal phylum inhabiting a bro ...
s. The earliest known true members of the group are known from
Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...
(145 to 66 million years ago) amber, found in North America, but are essentially modern forms, and therefore likely have a significantly earlier origin, as they diverged from their closest relatives in the
Cambrian
The Cambrian Period ( ; sometimes symbolized Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million years ago ...
, over 500 million years ago.
Tardigrades are usually about long when fully grown.
They are short and plump, with four pairs of legs, each ending in claws (usually four to eight) or suction disks.
Tardigrades are prevalent in
moss
Mosses are small, non-vascular flowerless plants in the taxonomic division Bryophyta (, ) '' sensu stricto''. Bryophyta ('' sensu lato'', Schimp. 1879) may also refer to the parent group bryophytes, which comprise liverworts, mosses, and ...
es and
lichen
A lichen ( , ) is a composite organism that arises from algae or cyanobacteria living among filaments of multiple fungi species in a mutualistic relationship.[microscope
A microscope () is a laboratory instrument used to examine objects that are too small to be seen by the naked eye. Microscopy is the science of investigating small objects and structures using a microscope. Microscopic means being invisi ...]
, making them accessible to students and amateur scientists.
Naming
Johann August Ephraim Goeze originally named the tardigrade ''Kleiner Wasserbär'', meaning "little water-bear" in German (today, they are often referred to in German as ''Bärtierchen'' or "little bear-animal"). The name "water-bear" comes from the way they walk, reminiscent of a
bear
Bears are carnivoran mammals of the family Ursidae. They are classified as caniforms, or doglike carnivorans. Although only eight species of bears are extant, they are widespread, appearing in a wide variety of habitats throughout the No ...
's
gait
Gait is the pattern of movement of the limbs of animals, including humans, during locomotion over a solid substrate. Most animals use a variety of gaits, selecting gait based on speed, terrain, the need to maneuver, and energetic efficiency. ...
. The name ''Tardigradum'' means "slow walker" and was given by
Lazzaro Spallanzani in 1777.
Description
![Waterbear](https://upload.wikimedia.org/wikipedia/commons/0/08/Waterbear.jpg)
The largest adults may reach a body length of , the smallest below . Newly hatched tardigrades may be smaller than .
Habitat
Tardigrades are often found on lichens and mosses, for example by soaking a piece of moss in water. Other environments in which they are found include
dune
A dune is a landform composed of wind- or water-driven sand. It typically takes the form of a mound, ridge, or hill. An area with dunes is called a dune system or a dune complex. A large dune complex is called a dune field, while broad, f ...
s and
coast
The coast, also known as the coastline or seashore, is defined as the area where land meets the ocean, or as a line that forms the boundary between the land and the coastline. The Earth has around of coastline. Coasts are important zones in n ...
s generally,
soil
Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former ...
,
leaf litter
Plant litter (also leaf litter, tree litter, soil litter, litterfall or duff) is dead plant material (such as leaves, bark, needles, twigs, and cladodes) that have fallen to the ground. This detritus or dead organic material and its constituent ...
, and
marine
Marine is an adjective meaning of or pertaining to the sea or ocean.
Marine or marines may refer to:
Ocean
* Maritime (disambiguation)
* Marine art
* Marine biology
* Marine debris
* Marine habitats
* Marine life
* Marine pollution
Military ...
or
freshwater
Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does incl ...
sediments, where they may occur quite frequently, up to 25,000 animals per litre (95,000 animals per gallon). One tardigrade, ''Echiniscoides wyethi'',
may be found on
barnacle
A barnacle is a type of arthropod constituting the subclass Cirripedia in the subphylum Crustacea, and is hence related to crabs and lobsters. Barnacles are exclusively marine, and tend to live in shallow and tidal waters, typically in erosiv ...
s.
Anatomy and morphology
Tardigrades have barrel-shaped bodies with four pairs of stubby legs. Most range from in length, although the largest species may reach .
The body consists of a head, three body
segments each with a pair of legs, and a
caudal
Caudal may refer to:
Anatomy
* Caudal (anatomical term) (from Latin ''cauda''; tail), used to describe how close something is to the trailing end of an organism
* Caudal artery, the portion of the dorsal aorta of a vertebrate that passes into the ...
segment with a fourth pair of legs. The legs are without
joints, while the feet have four to eight claws each. The
cuticle
A cuticle (), or cuticula, is any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of "cuticle" are non- homologous, differing in their origin, structu ...
contains
chitin
Chitin ( C8 H13 O5 N)n ( ) is a long-chain polymer of ''N''-acetylglucosamine, an amide derivative of glucose. Chitin is probably the second most abundant polysaccharide in nature (behind only cellulose); an estimated 1 billion tons of chit ...
and
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...
and is
moulted periodically. The first three pairs of legs are directed downward along the sides and are the primary means of locomotion, while the fourth pair is directed backward on the last segment of the trunk and is used primarily for grasping the substrate.
Tardigrades lack several
Hox gene
Hox genes, a subset of homeobox genes, are a group of related genes that specify regions of the body plan of an embryo along the head-tail axis of animals. Hox proteins encode and specify the characteristics of 'position', ensuring that the cor ...
s and a large intermediate region of the body axis. In insects, this corresponds to the entire thorax and the abdomen. Practically the whole body, except for the last pair of legs, is made up of just the segments that are homologous to the head region in arthropods.
All adult tardigrades of the same species have the same number of cells (see
eutely). Some species have as many as 40,000 cells in each adult, while others have far fewer.
The body cavity consists of a
haemocoel, but the only place where a true
coelom
The coelom (or celom) is the main body cavity in most animals and is positioned inside the body to surround and contain the digestive tract and other organs. In some animals, it is lined with mesothelium. In other animals, such as molluscs, ...
can be found is around the
gonad
A gonad, sex gland, or reproductive gland is a mixed gland that produces the gametes and sex hormones of an organism. Female reproductive cells are egg cells, and male reproductive cells are sperm. The male gonad, the testicle, produces sp ...
. No respiratory organs are found, with gas exchange able to occur across the entirety of the body. Some tardigrades have three tubular glands associated with the rectum; these may be excretory organs similar to the
Malpighian tubules of
arthropod
Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chiti ...
s, although the details remain unclear.
[ Also, nephridia are absent.
The tubular mouth is armed with stylets, which are used to pierce the plant cells, ]algae
Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular micr ...
, or small invertebrates on which the tardigrades feed, releasing the body fluids or cell contents. The mouth opens into a triradiate, muscular, sucking pharynx
The pharynx (plural: pharynges) is the part of the throat behind the mouth and nasal cavity, and above the oesophagus and trachea (the tubes going down to the stomach and the lungs). It is found in vertebrates and invertebrates, though its st ...
. The stylets are lost when the animal molts, and a new pair is secreted from a pair of glands that lie on either side of the mouth. The pharynx connects to a short esophagus
The esophagus (American English) or oesophagus (British English; both ), non-technically known also as the food pipe or gullet, is an organ in vertebrates through which food passes, aided by peristaltic contractions, from the pharynx to t ...
, and then to an intestine that occupies much of the length of the body, which is the main site of digestion. The intestine opens, via a short rectum, to an anus
The anus (Latin, 'ring' or 'circle') is an opening at the opposite end of an animal's digestive tract from the mouth. Its function is to control the expulsion of feces, the residual semi-solid waste that remains after food digestion, which, ...
located at the terminal end of the body. Some species only defecate when they molt, leaving the feces behind with the shed cuticle.
The brain develops in a bilaterally symmetric
Symmetry in biology refers to the symmetry observed in organisms, including plants, animals, fungi, and bacteria. External symmetry can be easily seen by just looking at an organism. For example, take the face of a human being which has a pl ...
pattern. Tardigrades have a dorsal brain atop a paired ventral nervous system. The brain includes multiple lobes, mostly consisting of three bilaterally paired clusters of neuron
A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa ...
s. The brain is attached to a large ganglion
A ganglion is a group of neuron cell bodies in the peripheral nervous system. In the somatic nervous system this includes dorsal root ganglia and trigeminal ganglia among a few others. In the autonomic nervous system there are both sympathe ...
below the esophagus, from which a double ventral nerve cord
The ventral nerve cord is a major structure of the invertebrate central nervous system. It is the functional equivalent of the vertebrate spinal cord. The ventral nerve cord coordinates neural signaling from the brain to the body and vice versa, i ...
runs the length of the body. The cord possesses one ganglion per segment, each of which produces lateral nerve fibres that run into the limbs. Many species possess a pair of rhabdomeric pigment-cup eyes, and numerous sensory bristles are on the head and body.
Tardigrades all possess a buccopharyngeal apparatus (swallowing device made of muscles and spines that activates an inner jaw and begins digestion and movement along the throat and intestine) which, along with the claws, is used to differentiate species.
Reproduction
Although some species are parthenogenic, both males and females are usually present, although females are frequently larger and more common. Both sexes have a single gonad
A gonad, sex gland, or reproductive gland is a mixed gland that produces the gametes and sex hormones of an organism. Female reproductive cells are egg cells, and male reproductive cells are sperm. The male gonad, the testicle, produces sp ...
located above the intestine. Two ducts run from the testes in males, opening through a single pore in front of the anus. In contrast, females have a single duct opening either just above the anus or directly into the rectum, which forms a cloaca
In animal anatomy, a cloaca ( ), plural cloacae ( or ), is the posterior orifice that serves as the only opening for the digestive, reproductive, and urinary tracts (if present) of many vertebrate animals. All amphibians, reptiles and birds, ...
.[
Tardigrades are ]oviparous
Oviparous animals are animals that lay their eggs, with little or no other embryonic development within the mother. This is the reproductive method of most fish, amphibians, most reptiles, and all pterosaurs, dinosaurs (including birds), and m ...
, and fertilization is usually external. Mating occurs during the molt with the eggs being laid inside the shed cuticle
A cuticle (), or cuticula, is any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of "cuticle" are non- homologous, differing in their origin, structu ...
of the female and then covered with sperm. A few species have internal fertilization, with mating occurring before the female fully sheds her cuticle. In most cases, the eggs are left inside the shed cuticle to develop, but some species attach them to nearby substrate.[
The eggs hatch after no more than 14 days, with the young already possessing their full complement of adult ]cells
Cell most often refers to:
* Cell (biology), the functional basic unit of life
Cell may also refer to:
Locations
* Monastic cell, a small room, hut, or cave in which a religious recluse lives, alternatively the small precursor of a monastery w ...
. Growth to the adult size occurs by enlargement of the individual cells (hypertrophy
Hypertrophy is the increase in the volume of an organ or tissue due to the enlargement of its component cells. It is distinguished from hyperplasia, in which the cells remain approximately the same size but increase in number.Updated by Linda J. ...
), rather than by cell division. Tardigrades may molt up to 12 times.[
Tardigrades tend to court before mating. Courtship is an early step in mating and was first observed in tardigrades in 1895. Research shows that up to nine males aggregate around a female to mate.
]
Ecology and life history
Most tardigrades are phytophagous (plant eaters) or bacteriophagous (bacteria eaters), but some are carnivorous
A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other ...
to the extent that they eat smaller species of tardigrades (e.g., '' Milnesium tardigradum'').
Tardigrades share morphological characteristics with many species that differ largely by class. Biologists have a difficult time finding verification among tardigrade species because of this relationship. These animals are most closely related to the early evolution of arthropod
Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chiti ...
s. Tardigrade fossils go as far back as the Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...
period in North America. Tardigrades are considered cosmopolitan and can be located in regions all over the world. The eggs and cysts of tardigrades are so durable that they can be carried great distances on the feet of other animals.
Tardigrades have survived all five recognized mass extinction
An extinction event (also known as a mass extinction or biotic crisis) is a widespread and rapid decrease in the biodiversity on Earth. Such an event is identified by a sharp change in the diversity and abundance of multicellular organisms. It ...
s due to their plethora of survival characteristics, including the ability to survive conditions that would be fatal to almost all other animals (see the next section).
The lifespan of tardigrades ranges from three to four months for some species, up to two years for other species, not counting their time in dormant states.
Physiology
Scientists have reported tardigrades in hot spring
A hot spring, hydrothermal spring, or geothermal spring is a spring produced by the emergence of geothermally heated groundwater onto the surface of the Earth. The groundwater is heated either by shallow bodies of magma (molten rock) or by circ ...
s, on top of the Himalayas
The Himalayas, or Himalaya (; ; ), is a mountain range in Asia, separating the plains of the Indian subcontinent from the Tibetan Plateau. The range has some of the planet's highest peaks, including the very highest, Mount Everest. Over 100 ...
(6,000 m; 20,000 ft, above sea level) to the deep sea () and from the polar region
The polar regions, also called the frigid geographical zone, zones or polar zones, of Earth are the regions of the planet that surround its geographical poles (the North Pole, North and South Poles), lying within the polar circles. These high l ...
s to the equator
The equator is a circle of latitude, about in circumference, that divides Earth into the Northern and Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the North and South poles. The term can als ...
, under layers of solid ice
Ice is water frozen into a solid state, typically forming at or below temperatures of 0 degrees Celsius or Depending on the presence of impurities such as particles of soil or bubbles of air, it can appear transparent or a more or less opaq ...
, and in ocean sediments. Many species can be found in milder environments such as lakes, ponds, and meadow
A meadow ( ) is an open habitat, or field, vegetated by grasses, herbs, and other non-woody plants. Trees or shrubs may sparsely populate meadows, as long as these areas maintain an open character. Meadows may be naturally occurring or artifi ...
s, 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.
Tardigrades are thought to be able to survive even complete global mass extinction event
An extinction event (also known as a mass extinction or biotic crisis) is a widespread and rapid decrease in the biodiversity on Earth. Such an event is identified by a sharp change in the diversity and abundance of multicellular organisms. I ...
s caused by astrophysical events, such as gamma-ray bursts
In gamma-ray astronomy, gamma-ray bursts (GRBs) are immensely energetic explosions that have been observed in distant galaxies. They are the most energetic and luminous electromagnetic events since the Big Bang. Bursts can last from ten millise ...
, or large meteorite impacts. Some of them can withstand extremely cold temperatures down to (close to absolute zero
Absolute zero is the lowest limit of the thermodynamic temperature scale, a state at which the enthalpy and entropy of a cooled ideal gas reach their minimum value, taken as zero kelvin. The fundamental particles of nature have minimum vibration ...
), while others can withstand extremely hot temperatures up to for several minutes, pressures about six times greater than those found in the deepest ocean trenches, ionizing radiation
Ionizing radiation (or ionising radiation), including nuclear radiation, consists of subatomic particles or electromagnetic waves that have sufficient energy to ionize atoms or molecules by detaching electrons from them. Some particles can travel ...
at doses hundreds of times higher than the lethal dose for a human, and the vacuum of outer space. Tardigrades that live in harsh conditions undergo an annual process of cyclomorphosis Cyclomorphosis (also known as seasonal polyphenism) is the name given to the occurrence of cyclic or seasonal changes in the phenotype of an organism through successive generations.
It occurs in small aquatic invertebrates that reproduce by parthen ...
, allowing for survival in subzero temperatures.
They are not considered extremophilic
An extremophile (from Latin ' meaning "extreme" and Greek ' () meaning "love") is an organism that is able to live (or in some cases thrive) in extreme environments, i.e. environments that make survival challenging such as due to extreme tempe ...
because they are not adapted to exploit these conditions, only to endure them. This means that their chances of dying increase the longer they are exposed to the extreme environments, whereas true extremophile
An extremophile (from Latin ' meaning "extreme" and Greek ' () meaning "love") is an organism that is able to live (or in some cases thrive) in extreme environments, i.e. environments that make survival challenging such as due to extreme temper ...
s thrive in a physically or geochemical
Geochemistry is the science that uses the tools and principles of chemistry to explain the mechanisms behind major geological systems such as the Earth's crust and its oceans. The realm of geochemistry extends beyond the Earth, encompassing the e ...
ly extreme environment
An extreme environment is a habitat that is considered very hard to survive in due to its considerably extreme conditions such as temperature, accessibility to different energy sources or under high pressure. For an area to be considered an extrem ...
that would harm most other organisms.
Tardigrades are one of the few groups of species that are capable of suspending their metabolism (see cryptobiosis
Cryptobiosis or anabiosis is a metabolic state of life entered by an organism in response to adverse environmental conditions such as desiccation, freezing, and oxygen deficiency. In the cryptobiotic state, all measurable metabolic processes stop ...
). While in this state, their metabolism lowers to less than 0.01% of normal and their water content can drop to 1% of normal, and they can go without food or water for more than 30 years, only to later rehydrate, forage, and reproduce. Many species of tardigrade can survive in a dehydrated state up to five years, or longer in exceptional cases. Depending on the environment, they may enter this state via anhydrobiosis
Cryptobiosis or anabiosis is a metabolic state of life entered by an organism in response to adverse environmental conditions such as desiccation, freezing, and oxygen deficiency. In the cryptobiotic state, all measurable metabolic processes sto ...
, allowing tardigrades, along with some other micro-metazoans (such as worms, rotifers, and crustaceans), protozoans, and plants that ability to survive in inhospitable habitats as opposed to other living things. In addition to offering protection from desiccation and freezing under normal circumstances, anhydrobiosis also permits resistance to unnatural abiotic extremes such as subzero temperatures. cryobiosis, osmobiosis, or anoxybiosis.
Their ability to remain desiccated for such long periods of time was thought to be dependent on high levels of the nonreducing disaccharide trehalose
Trehalose (from Turkish '' tıgala'' – a sugar derived from insect cocoons + -ose) is a sugar consisting of two molecules of glucose. It is also known as mycose or tremalose. Some bacteria, fungi, plants and invertebrate animals synthesize it ...
, which is commonly seen in other organisms that survive desiccation, and tardigrades have trehalase
The enzyme Trehalase is a glycoside hydrolase, produced by cells in the brush border of the small intestine, which catalyzes the conversion of trehalose to glucose. It is found in most animals.
The non-reducing disaccharide trehalose (α-D-glucop ...
gene
In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...
s. However, it has been seen that in both tardigrades and bdelloid rotifers
Bdelloidea (Greek ''βδέλλα'', ''bdella'', "leech") is a class of rotifers found in freshwater habitats all over the world. There are over 450 described species of bdelloid rotifers (or 'bdelloids'), distinguished from each other mainl ...
, there is only a partial capability to synthesize trehalose in quantities that may contribute to desiccation tolerance.[
In response to this finding, more research was done on how these animals survived such extreme conditions. It was found that ]intrinsically disordered proteins
In molecular biology, an intrinsically disordered protein (IDP) is a protein that lacks a fixed or ordered three-dimensional structure, typically in the absence of its macromolecular interaction partners, such as other proteins or RNA. IDPs ra ...
(IDPs) were highly expressed in response to desiccation in tardigrades. Additionally, three new IDPs were found to be specific to tardigrades and coined tardigrade specific proteins (TDPs). These TDPs may maintain the structure of membranes by associating with the polar heads of the phospholipids bilayers, avoiding structural damage upon rehydration. Also, TDPs, being highly hydrophilic, are thought to be involved in a vitrification mechanism, where a glass-like matrix forms within cells to protect the cellular contents upon desiccation. Their DNA is further protected from radiation by a protein called "dsup
Dsup (contraction of ''damage suppressor'') is a DNA-associating protein, unique to the tardigrade, that suppresses the occurrence of DNA breaks by radiation. When human HEK293 cells were engineered with Dsup proteins, they showed approximately 40 ...
" (short for ''damage suppressor''). In this cryptobiotic state, the tardigrade is known as a tun.
Tardigrades are able to survive in extreme environments that would kill almost any other animal.[ Extremes at which tardigrades can survive include those of:
* ]Temperature
Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer.
Thermometers are calibrated in various temperature scales that historically have relied o ...
– tardigrades can survive:
** A few minutes at
** 30 years at
** A few days at
** A few minutes at
Research published in 2020 shows that tardigrades are sensitive to high temperatures. Researchers showed it takes 48 hours at to kill half of active tardigrades that have not been acclimated to heat. Acclimation boosted the temperature needed to kill half of active tardigrades to . Tardigrades in the tun state fared a bit better, tolerating higher temperatures. It took heating to to kill half of tun-state tardigrades within one hour. Longer exposure time decreased the temperature needed for lethality, though. For 24 hours of exposure, was enough to kill half of the tun-state tardigrades.
* Pressure
Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and e ...
– they can withstand the extremely low pressure of a vacuum
A vacuum is a space devoid of matter. The word is derived from the Latin adjective ''vacuus'' for "vacant" or "void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often dis ...
and also very high pressures, more than 1,200 times atmospheric pressure
Atmospheric pressure, also known as barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. The standard atmosphere (symbol: atm) is a unit of pressure defined as , which is equivalent to 1013.25 millibars, 7 ...
. Some species can also withstand pressure of 6,000 atmospheres, which is nearly six times the pressure of water in the deepest ocean trench, the Mariana Trench
The Mariana Trench is an oceanic trench located in the western Pacific Ocean, about east of the Mariana Islands; it is the deepest oceanic trench on Earth. It is crescent-shaped and measures about in length and in width. The maximum know ...
. Tardigrades can survive altitudes of over 19,600 feet (6,000 meters) and to depths of over 15,000 feet (4,700 m) below the surface.
* Impact
Impact may refer to:
* Impact (mechanics), a high force or shock (mechanics) over a short time period
* Impact, Texas, a town in Taylor County, Texas, US
Science and technology
* Impact crater, a meteor crater caused by an impact event
* Impac ...
s – tardigrades can survive impacts up to about 900 meters per second, and momentary shock pressures up to about 1.14 gigapascal
The pascal (symbol: Pa) is the unit of pressure in the International System of Units (SI), and is also used to quantify internal pressure, stress, Young's modulus, and ultimate tensile strength. The unit, named after Blaise Pascal, is defined as ...
s.
* Dehydration
In physiology, dehydration is a lack of total body water, with an accompanying disruption of metabolic processes. It occurs when free water loss exceeds free water intake, usually due to exercise, disease, or high environmental temperature. Mil ...
– the longest that living tardigrades have been shown to survive in a dry state is nearly 10 years, although there is one report of leg movement, not generally considered "survival", in a 120-year-old specimen from dried moss. When exposed to extremely low temperatures, their body composition goes from 85% water to only 3%. Because water expands upon freezing, dehydration ensures the tardigrades' tissues are not ruptured by the expansion of freezing ice.
* Radiation
In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes:
* ''electromagnetic radiation'', such as radio waves, microwaves, infrared, visi ...
– tardigrades can withstand 1,000 times more radiation than other animals, median lethal doses of 5,000 Gy (of gamma rays) and 6,200 Gy (of heavy ions) in hydrated animals (5 to 10 Gy could be fatal to a human). The only explanation found in earlier experiments for this ability was that their lowered water state provides fewer reactants for ionizing radiation
Ionizing radiation (or ionising radiation), including nuclear radiation, consists of subatomic particles or electromagnetic waves that have sufficient energy to ionize atoms or molecules by detaching electrons from them. Some particles can travel ...
. However, subsequent research found that tardigrades, when hydrated, still remain highly resistant to shortwave UV radiation
Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation i ...
in comparison to other animals, and that one factor for this is their efficient ability to repair damage to their DNA resulting from that exposure.
:Irradiation of tardigrade eggs collected directly from a natural substrate (moss) showed a clear dose-related response, with a steep decline in hatchability at doses up to 4 kGy, above which no eggs hatched. The eggs were more tolerant to radiation late in development. No eggs irradiated at the early developmental stage hatched, and only one egg at middle stage hatched, while eggs irradiated in the late stage hatched at a rate indistinguishable from controls.
* Environmental toxins
A toxin is a naturally occurring organic matter, organic poison produced by metabolic activities of Life, living Cell (biology), cells or organisms. Toxins occur especially as a protein or conjugated protein. The term toxin was first used by orga ...
– tardigrades are reported to undergo chemobiosis, a cryptobiotic
Cryptobiosis or anabiosis is a metabolic state of life entered by an organism in response to adverse environmental conditions such as desiccation, freezing, and oxygen deficiency. In the cryptobiotic state, all measurable metabolic processes stop ...
response to high levels of environmental toxins. However, as of 2001, these laboratory results have yet to be verified.
Survival after exposure to outer space
Tardigrades are the first known animal to survive after exposure to outer space. In September 2007, dehydrated tardigrades were taken into low Earth orbit
A low Earth orbit (LEO) is an orbit around Earth with a period of 128 minutes or less (making at least 11.25 orbits per day) and an eccentricity less than 0.25. Most of the artificial objects in outer space are in LEO, with an altitude never mor ...
on the FOTON-M3
Foton (or Photon) is the project name of two series of Russian science satellite and reentry vehicle programs. Although uncrewed, the design was adapted from the crewed Vostok spacecraft capsule. The primary focus of the Foton project is materi ...
mission carrying the BIOPAN
BIOPAN is a multi-user research program by the European Space Agency (ESA) designed to investigate the effect of the space environment on biological material. The experiments in BIOPAN are exposed to solar and cosmic radiation, the space vacuu ...
astrobiology payload. For 10 days, groups of tardigrades, some of them previously dehydrated, some of them not, were exposed to the hard vacuum
A vacuum is a space devoid of matter. The word is derived from the Latin adjective ''vacuus'' for "vacant" or "void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often dis ...
of outer space, or vacuum and solar UV radiation. Back on Earth, more than 68% of the subjects protected from solar UV radiation were reanimated within 30 minutes following rehydration, although subsequent mortality was high; many of these produced viable embryos. In contrast, hydrated samples exposed to the combined effect of vacuum and full solar UV radiation had significantly reduced survival, with only three subjects of '' Milnesium tardigradum'' surviving. Also, it was found that the space vacuum did not have a significant effect on egg-laying in either R. ''coronifer'' or M. ''tardigradum''. However, M. ''tardigradum'' exposed to UV radiation had a lower egg laying rate. In May 2011, Italian scientists sent tardigrades on board the International Space Station along with extremophiles on STS-134
STS-134 ( ISS assembly flight ULF6) was the penultimate mission of NASA's Space Shuttle program and the 25th and last spaceflight of . This flight delivered the Alpha Magnetic Spectrometer and an ExPRESS Logistics Carrier to the International ...
, the final flight of . Their conclusion was that microgravity and cosmic radiation "did not significantly affect survival of tardigrades in flight, and stated that tardigrades represent a useful animal for space research." In November 2011, they were among the organisms to be sent by the U.S.-based Planetary Society
The Planetary Society is an American internationally-active non-governmental nonprofit organization. It is involved in research, public outreach, and political space advocacy for engineering projects related to astronomy, planetary science, and ...
on the Russian Fobos-Grunt
Fobos-Grunt or Phobos-Grunt (russian: link=no, Фобос-Грунт, where ''грунт'' refers to the ''ground'' in the narrow geological meaning of any type of soil or rock exposed on the surface) was an attempted Russian sample return mis ...
mission's Living Interplanetary Flight Experiment
The Living Interplanetary Flight ExperimentAsian Scientist"Phobos-Grunt Mission Carrying Yinghuo-1 Space Probe Suffers Technical Glitch" Srinivas Laxman, 9 November 2011 (LIFE or Phobos LIFE) was an interplanetary mission developed by the Planetar ...
to Phobos; however, the launch failed. In August 2019, scientists reported that a capsule containing tardigrades in a cryptobiotic state may have survived for a while on the Moon
The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...
after the April 2019 crash landing of ''Beresheet
''Beresheet'' ( he, בְּרֵאשִׁית, ''Bərēšīṯ'', "In the beginning"; Book of Genesis) was a demonstrator of a small robotic lunar lander and lunar probe operated by SpaceIL and Israel Aerospace Industries. Its aims included insp ...
'', a failed Israeli lunar lander, but in May 2021 it was reported that they were unlikely to have survived the impact.
In recent years, there has also been increased speculation regarding tardigrades' ability to survive on Mars without any life support systems, but despite the hardiness of the tardigrade, it would still "need stuff to eat," in order to set up shop.
Taxonomy
Scientists have conducted morphological and molecular studies to understand how tardigrades relate to other lineages of ecdysozoan animals. Two plausible placements have been proposed: tardigrades are either most closely related to Arthropoda
Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and Arth ...
and Onychophora
Onychophora (from grc, ονυχής, , "claws"; and , , "to carry"), commonly known as velvet worms (due to their velvety texture and somewhat wormlike appearance) or more ambiguously as peripatus (after the first described genus, '' Peripatus ...
, or to nematodes
The nematodes ( or grc-gre, Νηματώδη; la, Nematoda) or roundworms constitute the phylum Nematoda (also called Nemathelminthes), with plant-parasitic nematodes also known as eelworms. They are a diverse animal phylum inhabiting a broa ...
. Evidence for the former is a common result of morphological studies; evidence of the latter is found in some molecular analyses.
The latter hypothesis has been rejected by recent microRNA
MicroRNA (miRNA) are small, single-stranded, non-coding RNA molecules containing 21 to 23 nucleotides. Found in plants, animals and some viruses, miRNAs are involved in RNA silencing and post-transcriptional regulation of gene expression. miRN ...
and expressed sequence tag analyses. Apparently, the grouping of tardigrades with nematodes found in a number of molecular studies is a long branch attraction
In phylogenetics, long branch attraction (LBA) is a form of systematic error whereby distantly related lineages are incorrectly inferred to be closely related. LBA arises when the amount of molecular or morphological change accumulated within a lin ...
artifact. Within the arthropod group (called panarthropoda
Panarthropoda is a proposed animal clade containing the extant phyla Arthropoda, Tardigrada (water bears) and Onychophora (velvet worms). Panarthropods also include extinct marine legged worms known as lobopodians ("Lobopodia"), a paraphylet ...
and comprising onychophora, tardigrades and euarthropoda
Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chitin, oft ...
), three patterns of relationship are possible: tardigrades sister to onychophora
Onychophora (from grc, ονυχής, , "claws"; and , , "to carry"), commonly known as velvet worms (due to their velvety texture and somewhat wormlike appearance) or more ambiguously as peripatus (after the first described genus, '' Peripatus ...
plus arthropods (the lobopodia
The lobopodians, members of the informal group Lobopodia (from the Greek language, Greek, meaning "blunt feet"), or the formally erected phylum Lobopoda Cavalier-Smith (1998), are panarthropods with stubby legs called lobopods, a term which may ...
hypothesis); onychophora sister to tardigrades plus arthropods (the tactopoda hypothesis); and onychophora sister to tardigrades. Recent analyses indicate that the panarthropoda group is monophyletic, and that tardigrades are a sister group of Antennopoda, the lineage consisting of arthropods
Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and Arth ...
and Onychophora
Onychophora (from grc, ονυχής, , "claws"; and , , "to carry"), commonly known as velvet worms (due to their velvety texture and somewhat wormlike appearance) or more ambiguously as peripatus (after the first described genus, '' Peripatus ...
.
The minute sizes of tardigrades and their membranous integuments make their fossil
A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...
ization both difficult to detect and highly unusual. The only known fossil specimens are those from mid-Cambrian
The Cambrian Period ( ; sometimes symbolized Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million years ago ...
deposits in Siberia
Siberia ( ; rus, Сибирь, r=Sibir', p=sʲɪˈbʲirʲ, a=Ru-Сибирь.ogg) is an extensive geographical region, constituting all of North Asia, from the Ural Mountains in the west to the Pacific Ocean in the east. It has been a part of ...
(Orsten fauna
The Orsten fauna are fossilized organisms preserved in the Orsten lagerstätten of Cambrian (Late Miaolingian to Furongian) rocks, notably at Kinnekulle and on the island of Öland, all in Sweden.
The initial site, discovered in 1975 by Klaus Mü ...
) and a few rare specimens from Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...
amber
Amber is fossilized tree resin that has been appreciated for its color and natural beauty since Neolithic times. Much valued from antiquity to the present as a gemstone, amber is made into a variety of decorative objects."Amber" (2004). In Ma ...
.
The Siberian tardigrade fossils 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, but they share with modern tardigrades their columnar cuticle construction. Scientists think they represent a stem group of living tardigrades.
In October 2021, a new species, '' Paradoryphoribius chronocaribbeus'', was discovered as a fossil in amber that was dated to be 16 million years old.
Evolutionary history
There are multiple lines of evidence that tardigrades are secondarily miniaturized from a larger ancestor, probably a lobopodian
The lobopodians, members of the informal group Lobopodia (from the Greek language, Greek, meaning "blunt feet"), or the formally erected phylum Lobopoda Cavalier-Smith (1998), are panarthropods with stubby legs called lobopods, a term which may ...
and perhaps resembling ''Aysheaia
''Aysheaia'' is an extinct genus of soft-bodied lobopod, known from the middle Cambrian of North America, with an average body length of 1–6 cm.
Anatomy
''Aysheaia'' has ten body segments, each of which has a pair of spiked, annulate le ...
'', which many analyses place close to the divergence of the tardigrade lineage. An alternative hypothesis derives tactopoda from a clade encompassing dinocaridids and ''Opabinia
''Opabinia regalis'' is an extinct, stem group arthropod found in the Middle Cambrian Burgess Shale Lagerstätte (505 million years ago) of British Columbia. ''Opabinia'' was a soft-bodied animal, measuring up to 7 cm in body length, and it ...
''.
The oldest remains of modern tardigrades are those of '' Milnesium swolenskyi,'' belonging to the living genus ''Milnesium
''Milnesium'' is a genus of tardigrades. It is rather common, being found in a wide variety of habitats across the world. It has a fossil record extending back to the Cretaceous, the oldest species found so far (''M. swolenskyi'') is known from T ...
'' known from a Late Cretaceous
The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', the ...
(Turonian
The Turonian is, in the ICS' geologic timescale, the second age in the Late Cretaceous Epoch, or a stage in the Upper Cretaceous Series. It spans the time between 93.9 ± 0.8 Ma and 89.8 ± 1 Ma (million years ago). The Turonian is preceded by t ...
) aged specimen of New Jersey amber
New Jersey Amber, sometimes called Raritan amber, is amber found in the Raritan and Magothy Formations of the Central Atlantic (Eastern) coast of the United States. It is dated to the Late Cretaceous, Turonian age, based on pollen analysis of th ...
, around 90 million years old. Another fossil, '' Beorn leggi'', is known from a Late Campanian
The Campanian is the fifth of six ages of the Late Cretaceous Epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campanian s ...
(~72 million years old) specimen of Canadian amber
Canadians (french: Canadiens) are people identified with the country of Canada. This connection may be residential, legal, historical or cultural. For most Canadians, many (or all) of these connections exist and are collectively the source of ...
and has been placed in its own family (Beornidae), but was subsequently suggested to belong to the Hypsibiidae
The Hypsibiidae are a family of water bears or moss piglets, tardigrades in the class Eutardigrada.
Subfamilies and genera
* Subfamily Diphasconinae
** '' Diphascon''
** '' Hebesuncus''
** '' Paradiphascon''
* Subfamily Hypsibiinae
** '' Acu ...
. An indeterminate heterotardigrade was also noted from the same deposit.
Genomes and genome sequencing
Tardigrade genome
In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding ge ...
s vary in size, from about 75 to 800 megabase pair
A base pair (bp) is a fundamental unit of double-stranded nucleic acids consisting of two nucleobases bound to each other by hydrogen bonds. They form the building blocks of the DNA double helix and contribute to the folded structure of both DNA ...
s of DNA. ''Hypsibius exemplaris
''Hypsibius dujardini sensu lato'' is a species complex of tardigrade in the class Eutardigrada
Eutardigrada are a class of tardigrades (Tardigrada) without lateral appendices. Primarily freshwater bound, some species have secondarily gained ...
'' (formerly ''Hypsibius dujardini'') has a compact genome of 100 megabase pairs and a generation time of about two weeks; it can be cultured indefinitely and cryopreserved.
The genome of ''Ramazzottius varieornatus,'' one of the most stress-tolerant species of tardigrades, was sequenced by a team of researchers from the University of Tokyo
, abbreviated as or UTokyo, is a public research university located in Bunkyō, Tokyo, Japan. Established in 1877, the university was the first Imperial University and is currently a Top Type university of the Top Global University Project by ...
in 2015. While previous research had claimed that around one-sixth of the genome had been acquired from other organisms, it is now known that less than 1.2% of its genes were the result of horizontal gene transfer
Horizontal gene transfer (HGT) or lateral gene transfer (LGT) is the movement of genetic material between Unicellular organism, unicellular and/or multicellular organisms other than by the ("vertical") transmission of DNA from parent to offsprin ...
. They also found evidence of a loss of gene pathways that are known to promote damage due to stress. This study also found a high expression of novel tardigrade-unique proteins, including Damage suppressor (Dsup), which was shown to protect against DNA damage from X-ray
An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...
radiation. The same team applied the Dsup protein to human cultured cells and found that it suppressed X-ray damage to the human cells by around 40%. While the exact mechanism of DNA protection is largely unknown, the results from an August 2020 study suggest that strong electrostatic attractions along with high protein flexibility help form a molecular aggregate, which allows Dsup to shield DNA.
Ecological importance
Many organisms that live in aquatic environments feed on species such as nematodes, tardigrades, bacteria, algae, mites, and collembolan
Springtails (Collembola) form the largest of the three lineages of modern hexapods that are no longer considered insects (the other two are the Protura and Diplura). Although the three orders are sometimes grouped together in a class called Ento ...
s. Tardigrades work as pioneer species by inhabiting new developing environments. This movement attracts other invertebrates to populate that space, while also attracting predators.[
]
In popular culture
* When the characters in the superhero films
A superhero film (or superhero movie) is a film that focuses on the actions of superheroes. Superheroes are individuals who possess superhuman abilities and are dedicated to protecting the public. These films typically feature action, adventu ...
''Ant-Man
Ant-Man is the name of several superheroes appearing in books published by Marvel Comics. Created by Stan Lee, Larry Lieber and Jack Kirby, Ant-Man's first appearance was in ''Tales to Astonish'' #27 (January 1962) but first appeared in costum ...
'' (2015) and ''Ant-Man and the Wasp
''Ant-Man and the Wasp'' is a 2018 American superhero film based on Marvel Comics featuring the characters Scott Lang / Ant-Man and Hope Pym / Wasp. Produced by Marvel Studios and distributed by Walt Disney Studios Motion Pictures, it is th ...
'' (2018) shrink themselves to enter the "Quantum Realm
Quantum mechanics is a fundamental theory in physics that provides a description of the physical properties of nature at the scale of atoms and subatomic particles. It is the foundation of all quantum physics including quantum chemistry, qua ...
", they encounter tardigrades.
* In the 2015 sci-fi horror film ''Harbinger Down
''Harbinger Down'' (also known as ''Inanimate'' in the United Kingdom) is a 2015 American independent science-fiction monster horror film written and directed by Alec Gillis and produced by Tom Woodruff Jr., the founders of the special effect ...
'', the characters have to deal with deadly mutated tardigrades.
* The second arc of the comic book '' Paper Girls'' (2015) features a pair of tardigrades that have been enlarged to a massive size as a side effect of time travel.
* Musician Cosmo Sheldrake
Cosmo Christopher Sheldrake is an English musician, composer, and producer. He is the son of parapsychologist Rupert Sheldrake and voice teacher Jill Purce, and the brother of biologist Merlin Sheldrake. He released his first single, "The Moss ...
imagines himself a tardigrade in his 2015 "Tardigrade Song".
* In '' Star Trek: Discovery'' (2017), the alien "Ripper" creature who is used to "navigate" through a galactic mycelium
Mycelium (plural mycelia) is a root-like structure of a fungus consisting of a mass of branching, thread-like hyphae. Fungal colonies composed of mycelium are found in and on soil and many other substrate (biology), substrates. A typical single ...
network and instantly move the ship from one location in the galaxy to another is referred to as a "giant space tardigrade" and said to be a cousin of the tardigrade.
* The 2017 ''South Park
''South Park'' is an American animated sitcom created by Trey Parker and Matt Stone and developed by Brian Graden for Comedy Central. The series revolves around four boys Stan Marsh, Kyle Broflovski, Eric Cartman, and Kenny McCormickand th ...
'' episode " Moss Piglets" involves a science experiment in which tardigrades learn to dance to the music of Taylor Swift
Taylor Alison Swift (born December 13, 1989) is an American singer-songwriter. Her discography spans multiple genres, and her vivid songwriting—often inspired by her personal life—has received critical praise and wide media coverage. Bor ...
.
* The 2018 ''Family Guy
''Family Guy'' is an American animated sitcom originally conceived and created by Seth MacFarlane for the Fox Broadcasting Company. The show centers around the Griffin family, Griffins, a dysfunctional family consisting of parents Peter Griff ...
'' episode "Big Trouble in Little Quahog
The seventeenth season of '' Family Guy'' aired on Fox in the United States from September 30, 2018, to May 12, 2019.
The series follows the dysfunctional Griffin family, consisting of father Peter, mother Lois, daughter Meg, son Chris, baby ...
" features Stewie and Brian
Brian (sometimes spelled Bryan in English) is a male given name of Irish and Breton origin, as well as a surname of Occitan origin. It is common in the English-speaking world.
It is possible that the name is derived from an Old Celtic word me ...
being shrunk to a microscopic level, during which they meet a group of friendly tardigrades or "water bears" who help them.
* The plot in the 2021 '' Sam & Max: This Time It's Virtual'' video game includes an abandoned tardigrade amusement park, "Cap'N Aquabear's Funtime Park".
See also
* List of tardigrades of South Africa
* List of microorganisms tested in outer space
The survival of some microorganisms exposed to outer space has been studied using both simulated facilities and low Earth orbit exposures. Bacteria were some of the first organisms investigated, when in 1960 a Russian satellite carried ''Escherich ...
* Living Interplanetary Flight Experiment
The Living Interplanetary Flight ExperimentAsian Scientist"Phobos-Grunt Mission Carrying Yinghuo-1 Space Probe Suffers Technical Glitch" Srinivas Laxman, 9 November 2011 (LIFE or Phobos LIFE) was an interplanetary mission developed by the Planetar ...
, study of selected microorganisms in outer space
* Panspermia
Panspermia () is the hypothesis, first proposed in the 5th century BCE by the Greek philosopher Anaxagoras, that life exists throughout the Universe, distributed by space dust, meteoroids, asteroids, comets, and planetoids, as well as by spacecraf ...
References
External links
Tardigrada Register
*
{{Authority control
Extant Cambrian first appearances
Polyextremophiles
Psychrophiles
Radiodurants
Space-flown life
Thermophiles
Xerophiles
Tactopoda