iLabs: Catch of the Day — Water Bear

Here is another entry in our “Catch of the Day” series, by Nancy Locquet-Absillis

iLabs: “Catch Of The Day!” — Water bear, water bear, how DO you survive?

Look how cuddly! A rather clumsy, barrel-shaped microorganism moves like a bear on the slide we’ve placed under the microscope. Since its segmented body is transparent, you can see food in its stomach. With four pair of legs it’s clinging on to some substrate, which is usually moss or algae. The 8 stubby-looking legs are not segmented and seem to end in about 4 to 8 bear-like claws called discs. The discs are very flexible and can hold on firmly to algae, while the creature is searching for food.

The creature is known by a few names:  water bear, moss piglet,  or tardigrade, and it is a water-dwelling, segmented, 8-legged micro-animal.

Tardigrade eating algae and moss.

What’s that, you say? There’s not a lot of food in a drop of pond water?  On the contrary, the water bear is submerged in its food!

Its tube-like mouth has a special piercing device called a stylet to puncture through plants cells, algae or even small invertebrates. Once inside its prey, the stylet opens up so it will not pull out, and like a vampire, the water bear sucks up the cell content of plants and algae … or the body fluids of its victim/meal.  It seems just a touch ferocious for such a cute-looking teddy-bear-like organism.

As small as it is (and that would be about 0.5 mm to 1.5 mm when they are full grown), it has a complete digestive system with esophagus, an intestine the size of its body, a very short rectum and anus. Some species only defecate, leaving the feces in its “shed.”

Molting is an elaborate process and takes about 5-10 days. Some staff members of the Micro World Investigate lab were so lucky to see it happen and they took a snapshot of this event. Look at this picture. You can clearly see how the body is separated from the shed when you look at the legs.

A tardigrade in the process of molting.

Water bears molt about 4 to 12 times during their 3 to 30 months of active lives. Since they lose their piercing mouthparts during molting, a tardigrade (a name given to this organism by Lazzaro Spallanzani in the late 1700s, which means “slow walker”) can’t eat until the molting process is finished.

One day, we were so fortunate to see eggs inside the shed of a water bear! About Thirteen eggs were deposited in this water bear’s shed. We haven’t seen the newly born hatchlings, since it take about 14 days for them to hatch and it’s simply impossible to keep them on the slide for that long.

Tardigrade eggs in a molted shed.

The hatchlings are born with a complete set of cells. This means that all tardigrades from the same species, no matter how big they are, have the same amount of cells (which would be about 40,000 cells).

The newborn tardigrades are smaller than 0.05 mm. They don’t grow by cell division like we do; their individual cells increase in size as they grow bigger.

Scientists believe that they have survived all 5 mass extinctions, making them one of the oldest surviving organisms on this planet. Fossil records show that they have been living on Earth some 530 million years!

How resilient is our superhero? Well, they survived the following situations:

• They were exposed to extreme high temperatures for a few minutes (151°C; 304°F) and extreme cold (−200°C; -328 °F) for a few days and survived! Even -272°C for a few minutes didn’t seem to have an impact on them.
• Freezing and/or thawing conditions didn’t bother them.
• Lack of oxygen … they seem to be ok with it.
• Changes in salinity (changes in salt content of their environment) … not a problem.
• They can survive the vacuum and the solar radiation of outer space (1000 x the lethal dose for humans) for 10 days as well as extremely high pressure — up to 6,000 atmospheres, which is 6 times the water pressure in the deepest ocean trench.
• Ten years of extreme drought doesn’t seem to be a problem.
• Tardigrades can dry up completely and form a “tun” as they shrivel up into a little ball. They can be “revived” from this dead-like state once water is available. How can they possibly do this?  They possess a special sugar called trehalose which replaces the water in its body and preserves the body cells.
• They also survived being exposed to environmental toxins (chemicals such as boiling alcohol), although these lab tests still need to be confirmed.

It’s hard to believe that these amazing creatures have survived all this! Under normal circumstances they would only live for 1 year!

Would you like to see them in action? Come and visit the Micro World Investigate Lab.

While you’re there, try to find our blue water bear!

Blue stuffed tardigrade toy hidden on an upper lab shelf for visitors to find.