There are many species of tardigrade around the world, terrestrial species live in the moisture inside moss , lichen , litter and soil ; other species can be found in fresh or salt water . They are commonly known as water bears , a name derived from their strong resemblance to eight-legged pandas. Some call them mossy piglets and they have also been compared to rhinos and pygmy armadillos . These walking microscopic “moss bears”Eight legs are almost indestructible and represent a model organism for education .


What is a tardigrade?

The tardigrade, or water bear , is considered the last of the animals to become extinct from the earth. A micro animal that has eight legs turns out to be the toughest animal on the planet regardless of the type of catastrophe that exists.

  • Tardigrade characteristics
  • Habitat
  • Feeding
  • Reproduction of the tardigrade
  • Breathing
  • How long does a tardigrade live
  • They are dangerous?
  • Importance
  • Curiosities
  • Example species

Tardigrade characteristics

The main characteristics of the tardigrade are the following:

  • The so-called water bear is considered the hardest and most resistant form of life that exists on Earth.
  • Their size is approximately 0.5 millimeters and they have a half-life of 60 years.
  • It can go 30 years without eating or drinking , and withstands temperatures of up to 150 degrees .
  • It is capable of living in the abyssal depths .
  • They are invertebrate animals that have eight legs , have an elongated and oval shape .
  • They are almost translucent and with adequate light, they can be seen with the naked eye.
  • They have five body sections , a well- defined head and four body segments , each of these segments have a pair of legs which have claws .
  • The claws vary depending on the species. The hind legs are attached backwards, and they use them to grasp and make acrobatic movements in slow motion instead of walking.
  • They have similar anatomy and physiology to large animals, including a complete alimentary canal and digestive system .
  • They have a dorsal brain over a paired ventral nervous system.


Water bears generally inhabit water that forms on mosses , ferns, and lichens . When they do not have water around them, they are able to enter a state of rest indefinitely, until they manage to return to their normal cycle when they come into contact with water again. They are animals capable of surviving extreme conditions and for this reason their habitat can be any type of ecosystem that exists on planet earth . Their incredible ability to survive is due to a hibernation mechanismknown by the name of cryptobiosis .


This type of animal feed mainly on algae , bacteria and other microscopic invertebrates . The way to feed is by sucking the cells or gobbling up all their prey. Its digestive system has its main part in the mouth , which is made up of three cuticle rings that go to the interior cavity. It also has a tubular pharynx and a suction apparatus , covered with muscles that allow it to suck. Muscles have sclerosed structuresproviding rigidity to the inner tube and the mouth has two stylets sharp related to the suction system.

Reproduction of the tardigrade

Years ago it was known that tardigrades were bisexual but scientists suspected that their reproduction occurred externally . However, recent studies show that there is mutual stimulation between male and female, similar to humans. The female lays unfertilized eggs and sheds her cuticle , since the eggs are found inside it. The male places himself around the female and releases the semen on her, it reaches the female’s eggs and fertilizes them . When the female fails to fertilize the eggs, she reabsorbs them again.


Tardigrades do not have any type of respiratory system .

How long does a tardigrade live

The lifetime of tardigrades depends on the place where they are. They reproduce all over the planet, mainly in humid habitats . When these animals have enough food and water to be able to fulfill their bodily functions , they live the natural course of their lives, approximately 2.5 years . However, they are able to survive longer if they enter a state of cryptobiosis , which is activated when environmental conditions become unbearable .

Cryptobiosis causes tardigrades to surround themselves with a layer known as “tun,” which slows their metabolism to a halt, reducing their need for oxygen and almost completely discarding their water cells . In this way tardigrades mimic death and can survive in places without water, at temperatures as low as minus 200 degrees Celsius and as high as 151 degrees Celsius . When they are exposed to the water again, they revive themselves , returning to normal life in a matter of hours.

They are dangerous?

Tardigrades are not animals considered dangerous for humans so far, on the contrary, several experiments show that the resistance that these animals have to X-rays could be transferred to human cells . This could be vital for cell protection including cancer and aging . These experiments seek in the future to protect people against radiation and in the cure of some diseases .


Tardigrades are very important animals for their function as a model of research for science, mainly in the area of medicine ‘s because they have mechanisms regenerators of DNA , which can represent a huge advance in the study of genetics . Through biotechnology and genetic engineering they could isolate the genes responsible for allowing them to survive extremely adverse conditions. 


Some curiosities of the tardigrades are:

  • They are known by the name of “water bears” .
  • They look like little manatees .
  • It has the ability to enter a state of suspended animation for a period of up to one hundred years.
  • Their eggs look like small alien spacecraft .
  • Some of them can become carnivores .
  • They are the only animals that have the ability to survive in space .
  • The climate change does not affect them and are immune to X – rays

Example species

There are currently around 1,100 described species of water bears, but not all of them are valid. Some descriptions are repetitions and some are flawed. Around 1,000 species have been adequately identified and described. We have around 300 marine species , 100 freshwater and 600 terrestrial . There are three different types of tardigrades: heterotardigrades that have cephalic appendages and four-toed legs, eutardigrade, and mid – lateigrade that have six paws of equal size on each foot.

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