Tardigrades - Microscopic space travellers

Tardigrades are possibly some of the cutest and most popular microorganisms in the world. These microscopic animals can be found in all kinds of habitats all over the planet from high mountains to deep oceans, and even on the poles. However, even though they are very common almost everywhere you will need a microscope to spot them as most species are around 500 microns in size and the biggest ones rarely exceed 1 mm. Tardigrades are more commonly known as water bears, because of their bear-like appearance when they waddle around in the microworld looking for food. Some also call them moss piglets because of their high abundance in moss and lichen samples.

The darkfield illumination makes the individual storage cells clearly visible inside the body cavity, 

as well as the digestive system in the middle of the animal.

Tardigrades have eight legs which all end in a various number of claws depending on the species. Inside the body we find a lot of anatomical resemblance to larger animals as tardigrades both have a fully functioning nervous-, muscle-, and digestive system as well as primitive eyes. But despite a somewhat complex body structure, the animal only consists of a few thousand cells. Some of these are called storage cells which can be seen in the image above. These cells slush around inside of the animal when it walks. In the front tardigrades have a feeding apparatus consisting of stylets used to pierce the food and a pharynx used for chewing. Most tardigrades are herbivores and eat things like algae and other plant material. However, some species are hunters and eat things like bacteria, single celled organisms, rotifers and even other tardigrades.

They are sometimes referred to as extremophiles, due to their ability to survive extreme conditions like enormous amounts of pressure, temperatures from close to absolute zero to way past boiling as well as huge amounts of radiation. To test just how hardy these animals are, they were sent into space for 10 days back in 2007. Most of the tardigrades survived and were still able to reproduce afterwards, despite being exposed to the vacuum of space and blasted with cosmic radiation. But, to tolerate such extremes, the tardigrades need to enter an inactive state called a tun, where they lose almost all of their water and are essentially dead. When rehydrated, the tardigrades return from the dead and continue on with their lives as if nothing had happened.

A very few numbers of species have storage cells that shine in polarized light.

These microscopic gummy bear-looking animals are egg layers and can both reproduce sexually and asexually. Many species lay their eggs in their shed skin called the cuticle which they will outgrow several times throughout their lives. Other species will lay their eggs out in the open. After about one to two weeks the eggs will hatch. The newborn tardigrades have the same number of cells as an adult, and now they just need to grow. Tardigrades live from anywhere between a few months and up to two years in their active state. But if they enter the inactive state, they are able to survive for decades, maybe even centuries!

DOCUMENTARIES | EPISODE 01 | TARDIGRADES

The video features various species seen with different kinds of microscopy 

techniques at both low and high magnifications.