Facts about Tardigrades: Most Resilient Animal in The World

Tardigrade, an ever-interesting earth’s micro animal, was typically exposed into space without any spacesuit, and survived unharmed! Sounds strange, right? Let’s explore the unknown facts about Tardigrades.

Know the typical Species – Tardigrades

Tardigrades are the members of the phylum Tardigrada that means “slow waker”. It is also called a “little water bear” as it walks like a bear.

Where do tardigrades live?

Tardigrades can be found everywhere, from the deep sea to mountaintops, in the deep rainforest, hot spring volcanoes, even in the Antarctic. However, land-dwelling species are prevalent in mosses and lichens. They need water to survive and reproduce.

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Body structure of the animal

It is a very small animal that measures about 0.5 mm in length and has a plumpy caterpillar-like body with four pairs of legs, each ended up with 4 to 8 claws or suction discs. Its body is covered by a cuticle made up of chitin and proteins. Its tubular mouth is surrounded by many little stylets which shed along with the cuticle during each mounting and again regenerate. The mouth leads to a muscular pharynx that helps in the suction of food materials.

Facts about Tardigrades
Tardigrades under microscope (Photo credit: Guidetti Roberto)

Favorite Foods

They mainly feed on plant cells, bacteria, algae, and small invertebrates.

Life cycle of tardigrades

Both sexual and asexual reproduction occurs in tardigrades. Some species reproduce asexually by means of parthenogenesis (embryo develops into a female from the unfertilized egg) or through self-fertilization (hermaphroditism).

Female lays eggs into shed cuticle during molting. Eggs and cysts are very durable and withstand extreme environmental conditions. Eggs hatch around after 10-14 days, in a suitable environment, with the full set of complement adult cells. Newly born tardigrade grows by enlargement of the cells (hypertrophy) rather than cell division. Hatchling undergoes up to 12 molts (shedding of outer covering, the cuticle) to become an adult.

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Some Interesting Facts about Tardigrades

Undoutfully, tardigrades are strange animals owing to their typical characteristics. I’m introducing here some of the most unusual facts about Tardigrades that are unseen in any other living animals in the world.

Most Resilient Animal

Tardigrades are the most resilient animals known so far, which means they have the greatest ability to recover quickly from difficult conditions. They can withstand extreme environmental conditions such as temperature, pressure, drought, radiation, and even lack of oxygen for a long time. When suitable environmental condition returns they recover back to the normal life.

Below are the brief explanations of different environmental extremities, where the little water bear can survive.

Temperature toleranceSome tardigrades can withstand extremely cold temperatures almost close to absolute zero (-272°C), while some others can survive 150°C for several minutes.
High altitudeThey can be found at mountaintops. Scientists have reported their presence in hot springs of the Himalayas at a height of 6,000 m, where air pressure is extremely low. They are available even in mud volcanoes.
oceanic trench
Tardigrades can withstand high seawater pressure and found in deep-sea trenches, around 4,000 m below sea level, in complete darkness.
DesiccationTardigrades need plenty of water, that’s why it is called water bear. But according to some scientists and researchers, some species of tardigrades can stay without any water for several decades.
StarvationTardigrade starves for 30 years; have been reported to resume their life and reproduce again.

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Desiccated Tardigrade Live Longer Than Hydrated Ones

Tardigrades must need water to grow and reproduce, but in the case of their survival, the situation is somewhat different. An average lifespan of a regularly hydrated tardigrade is few months whereas according to some scientists and researchers desiccated specimens can live up to a century.

In several organisms undergoing desiccation a specialized sugar molecule called trehalose is found which helps them to survive drying.

When the tardigrade enters its desiccated state, in some species though trehalose substituting some of their cell contents are found present at low levels or not present at all in other species.

This indicates that tardigrades possess a potentially novel mechanism for surviving. In multiple species, tardigrade-specific disordered proteins (TDPs) are found at high levels during desiccation. TDPs from non-crystalline amorphous solids to cope with dehydration. TDP genes are consequently expressed at high levels. When tardigrades face harsh environmental conditions they quit almost all metabolisms, become dehydrated, go through deep sleep, and in this condition, they can survive for a very long time.

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Space Travel!

As we know, space is a terrible place for any living thing on earth to survive. But a group of desiccated tardigrades had survived open space for 10 days without any space suit! In space there is no air to breathe, no water to drink, freezing cold, incredibly dry, highly energic particles of sun’s radiation run at high speed without any filtration and traverse through the cells and destroy their molecules.

Space research on tardigrades
A group of scientists from Germany and Sweden worked together to send tardigrades into space. In 2007, a rocket ship was launched from Kazakhstan carrying four different species of desiccated tardigrades into small metal chambers fitted in a round box. They had picked four different species to observe if one is tougher than the others. Dried tardigrades were taken because they have the properties to withstand extremities. If hydrated tardigrades were chosen they just exploded in the harsh emptiness of space.

According to the mission, when the ship was just outside of Earth’s protection, the lid of the round box attached on the side of the ship containing little water bears opened. Tardigrades were the first animals exposed to the harsh emptiness of space without any spaceship or spacesuit. They stay there for 10 days then returned back. The lid was closed before returning. Some metal chambers had sun shades that blocked radiation from the sun, while others were not.

After returning the manless ship to earth, scientists observed how life was affected.

All tardigrades died which had no sun shades. The radiation from the sun shoots through the cells and destroyed cellular molecules resulting in their death. Thanks should be given to mother Earth for her protective shield from cosmic radiation providing a homely atmosphere on the earth’s surface.

Scientists had found hope when they observed the tardigrades enclosed in sun-protected chambers. Almost all of those specimens recover back to life. Some of them eventually reproduce to give new offsprings while others couldn’t!

So, they found that tardigrades can only survive space if they are protected from the radiation of the sun. However, they can’t live in space because they need water to grow and reproduce.

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Born with Whole set of Cells

Tardigrades are born with the number of cells same as the adults of the same species. Newborn has an average length of 0.1 mm, when they grow, instead of cell division each cell enlarges in size and reach about 1 cm in length. The development process includes cell division until maturity, further growth occurs via cell enlargement only. All adult tardigrades of the same species have the same number of cells as other eutectic organisms. Some species have as many as 40,000 cells in each adult, while others have fewer cells.

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Facts about Tardigrades: Conclusive Remarks

Tardigrades are very tough animals but definitely not the indestructible organisms as advertised on many websites. They can overcome many difficult situations by

going through a “tun” state. In this state they suspend their metabolisms to only 0.1% of the normal state, draw in their limbs, dehydrate and contract their bodies like a ball.

Though tardigrades can be chopped or squished to dead or if they are eaten by a human they can’t tolerate the stomach acid and die. But scientists believe that if a cataclysmic event wipes out most of life on earth including humans, tardigrades will be one of the leading animals surviving on the planet.

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Ms. Subhra Das is a biology teacher in high school by profession. Besides she is a passionate science writer and nature lover.

As a teacher, she never restricts herself within the four walls of the classroom, rather she loves exploring the crude science behind the natural facts that include human and animal health, critical diseases, typical characteristics of wildlife, and mother nature.

Ms. Subhra Das is also a passionate traveler and explorer; she always tries to uncover natural flora and fauna at every destination she travels.

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