June 7 (UPI) -- Move over water bears, rotifers are pretty tough too.
According to new research, Bdelloid rotifers, a class of microscopic invertebrates, can remain frozen for thousands of years and survive.
Recently, researchers at the Soil Cryology Lab -- part of the Institute of Physicochemical and Biological Problems in Soil Science, located in Russia -- reanimated a Bdelloid rotifer that had been frozen in Siberian permafrost for 24,000 years.
Scientists described the feat in a new paper, published Monday in the journal Current Biology.
"Our report is the hardest proof as of today that multicellular animals could withstand tens of thousands of years in cryptobiosis, the state of almost completely arrested metabolism," corresponding author Stas Malavin, with the Soil Cryology Lab, said in a news release.
Scientists have previously revived nematodes and grown plants from seeds found frozen in 30,000-year-old permafrost. Now, scientists have evidence that rotifers are equally hardy.
Rotifers are tiny worm-like animals than can extend and retract their bodies, which are organized around a spherical digestive tract. They are sometimes called wheel animals, due to the appearance mouths.
Past studies have shown that rotifers -- like tardigrades -- can survive prolonged dehydration and starvation, as well as persist in low-oxygen environs.
Previously, scientists estimated rotifers could last about a decade frozen. The latest radiocarbon analysis suggest that number is at least 24,000 years.
The rotifer that scientists brought back to life in the Soil Cryology Lab belongs to the genus Adineta. Not long after being thawed, the animal began to reproduce asexually via a clonal process called parthenogenesis.
Rotifers have been around for millions of years and are estimated to be some of the oldest asexually reproducing animals in the world.
The latest findings suggest that at least some of their evolutionary longevity can be explained by their knack for protecting themselves from extreme conditions.
"The takeaway is that a multicellular organism can be frozen and stored as such for thousands of years and then return back to life -- a dream of many fiction writers," Malavin said.
"Of course, the more complex the organism, the trickier it is to preserve it alive frozen and, for mammals, it's not currently possible. Yet, moving from a single-celled organism to an organism with a gut and brain, though microscopic, is a big step forward," Malavin said.
In followup studies, researchers said they hope to gain greater insights into the biological mechanisms rotifers use to protect their cells and organs from ice crystals during the freezing process.