When I saw the headline yesterday in the weird news that a new water bear had been discovered in Antarctica, I followed the link immediately, expecting to see a photo of a mammal and wondering how such a thing could have been missed all these years. It was then that I learned that a "water bear," also known as a moss piglet, is a microscopic invertebrate not more than 1 mm long (IMAGE ABOVE). It is a member of the tardigrade family, one of the hardiest creatures known. Water bears can withstand extremes of heat, cold, and pressure; dehydration; poison; radioactivity; and even the vacuum of space. Tardigrade specialist Sandra McInnes of the British Antarctic Survey was enlisted to help classify this southernmost species, which exhibits primitive characteristics suggesting that it is closer to the group's more distant ancestors. It hasn't evolved because, as she describes,"It doesn't seem to travel well."