Rotifers may be tougher than tardigrades

A microscopic creature known as the tardigrade, sometimes called a water bear, is extremely tough and resilient. They're so tough and resilient that NASA has been studying the microscopic creatures in an attempt to learn how they're able to survive incredibly harsh conditions such as being frozen for decades or being exposed directly to the vacuum of space. The tiny creatures were thought to be the toughest on the planet, but there's a creature that might be even tougher.The creature is called the Bdelloid rotifers, and it's being revived after being discovered frozen in the Siberian permafrost for the last 24,000 years. Not only were the tiny creatures able to continue living after being thawed out after that time span, they immediately began to reproduce when they were thawed. The creatures survived freezing by shutting themselves down almost completely into a state called cryptobiosis.

Creatures are also able to survive being dried, starvation, and being faced with low oxygen levels. Researchers on the project say the report is the hardest proof yet that multicellular animals could withstand tens of thousands of years in cryptobiosis, a state of almost entirely arrested metabolism. The sample the rotifers were discovered in was dug from the ancient permafrost in Siberia using a drilling rig.

Scientists on the project previously identified many single-celled microbes in the samples. For instance, there has been a report of a 30,000-year-old nematode worm being discovered along with mosses and some plants that have been regenerated after thousands of years trapped in the ice.

In the past, rotifers had been reported to survive up to a decade when frozen. The new study used radiocarbon dating to determine that the rotifers recovered from the permafrost were about 24,000 years old. The rotifers in question belong to the genus Adineta and can reproduce in a clonal process known as parthenogenesis. The study showed that rotifers could withstand the formation of ice crystals that occurred during slow freezing. It suggests the creatures have some sort of mechanism to shield their cells and organs from harm at extremely low temperatures. That exact mechanism is a mystery.