Tardigrade facts for kids

Tardigrada
	The tardigrade Hypsibius dujardini
Conservation status
	; Least Concern (IUCN 2.3)
Scientific classification
Kingdom:	Animalia
Superphylum:	Ecdysozoa
Phylum:	Tardigrada

Tardigrades ('water bears') are the phylum Tardigrada, part of the superphylum Ecdysozoa. They are microscopic, water-dwelling, segmented animals.

Tardigrades were first described in 1773. Their name means "slow stepper". There are more than 1000 different species of tardigrade.

Tardigrades have a cylindrical shape with four segments, each with two legs. Each leg has little claws. The biggest adults may reach a body length of 1.2 mm, the smallest below 0.1 mm. Freshly hatched larvae may be smaller than 0.05 mm. Tardigrades feed on plant cells by penetrating the cell wall and eating what is inside. Some tardigrades are carnivores.

Tardigrades are eutelic, meaning all adult tardigrades of the same species have the same number of cells. Some species have as many as 40,000 cells in each adult, while others have far fewer.

Tardigrades can be found in many habitats: in moss, freshwater, the Himalayas, and the ocean. They are one of the few animals that can be found on the highest mountains and the deepest seas. About 83 percent of the species live on land, the other 17 percent live in water.

Survivability

Tardigrades are able to live in environments that would kill most animals. In 2007, scientists discovered that some tardigrades were able to survive 10 days in outer space. Tardigrades can survive more than ten years without water. Tardigrates can survive a few hours in temperatures close to absolute zero and above boiling point.

Tardigrades can survive being frozen for over 30 years.

Images for kids

Johann August Ephraim Goeze
SEM image of Milnesium tardigradum in active state
Echiniscus testudo
Shed cuticle of female Tardigrade, containing eggs.
Hypsibius dujardini imaged with a scanning electron microscope
Illustration of Echiniscus sp. from 1861