My favorite animal is the water bear! They can survive extreme heat and cold, radiation levels, they can survive hundreds of years without food or water, and they can survive in space!! I think water bears beat koalas Hands down!
Ah, finally someone with a more unconventional favourite! And what a fabulous choice. There are hundreds of reasons why water bears (Tardigrada) are amazing animals. Tardigrades (meaning “slow walker” in Latin) are a phylum of over 1000 different species that are found everywhere in the world - from Himalayan peaks of over 6000 metres to ocean depths below 4000m, from icy polar regions to the heat of the tropics, in freshwater, saltwater and damp terrestrial habitats. If you’re wondering why such an abundant creature has so far escaped your notice, it’s because they are at their greatest 1.5mm and at their smallest, just 0.1mm long. But don’t dismiss them yet - they are most certainly one of the cutest and most interesting microscopic organisms out there!
Water bears have a body with four segments and four pairs of lobopodial (unjointed) legs each bearing a set of 4-8 little claws. They feed using a stylet, or small tube, with which they pierce plant or animal cells and then suck up the internal fluids. Of the many species of water bear, some are purely carnivorous, consuming bacteria, rotifers or other tardigrades, some are omnivorous, and some are herbivorous, eating only plant materials.
The most famous and interesting characteristic of water bears is that they can enter a state known as cryptobiosis if environmental conditions become insufficient to live in. In cryptobiosis, the tardigrade dries up into a form known as a ‘tun’ (containing less than 1% water) and its metabolic rate drops to a hundredth of a percent of its normal rate or may even be completely undetectable. It can remain like this for up to 100 years and only takes a few minutes to come ‘back to life’ once returned to favourable conditions! Cryptobiosis has a number of different triggers that activate slightly different pathways. These are drastic changes in water solute content such as ion concentration (osmobiosis), drought (anhydrobiosis), extreme temperatures (cryobiosis) or lack of oxygen (anoxybiosis). In their natural environment, the most common form of cryptobiosis is anhydrobiosis, but we’ve conducted all sorts of crazy experiments to see what else they can survive. They have sailed through several minutes at 151ºC, and several days below -200ºC. They can withstand extreme radiation at levels that would be lethal to almost all other animals. And tardigrades have even ventured into space, surviving 10 days of vacuum and cosmic radiation with 68% still retaining the ability to live and reproduce (the project is called TARDIS which just makes it all the better). Not only can they survive very low pressures as in the vacuum of space but also very high pressures, more than 1200 times greater than atmospheric pressure!
Finally, as with any great character the water bear even has its own cuddly toy. What more could you want from a favourite animal?!
Ref: Shifflett B. M., 2008. Tardigrades. University of Wisconsin Organismal Biology [link]
Lindahl K. & Balser S., 1999. Tardigrade Facts. Illinois Wesleyan University [link]
Goldstein B. & Blaxter M., 2002. Tardigrades. Current Biology 12(14):475. [link]