French researchers have found a new kind of virus so big they initially thought it must be something else.

The startling discovery, which upends some long-held assumptions about the nature of viruses — namely, that they are small — led the scientists to give it a fitting name: Pandoravirus.

"We believe we're opening a Pandora's box — not so much for humanity but for dogma about viruses," Dr. Jean-Michel Claverie, a co-author of the paper, tells the New York Times. "We believe we're touching an alternative tree of life."

In a study published in the journal Science, the researchers say that the Pandoravirus is so unique, it deserves its own classification. For one, the virus is twice as big as the second-largest known virus, and dwarfs the size of most others — it's volume is 1,000 times that of the common flu.

What's more, of its 2,556 genes, just seven percent match genes already identified by science. That, they say, suggests the virus grew out of a completely separate gene lineage from its peers.

Claverie and his colleagues first found the virus while digging in the sediment off the coast of Las Cruces, Chile. It was there that, in 2011, he and his team previously discovered the Megavirus — which, until now, was the biggest known virus in the world — and he was curious to see what else might be hiding in those waters.

The researchers later found a second massive Pandoravirus in a pond in Melbourne, Australia. The Chilean strain is known as Pandoravirus salinus, while the Australian find is Pandoravirus dulcis.

The new virus not only broadens our concept of how big viruses can be, but could unlock new information on how viruses work, and whether they fill in gaps in the evolutionary chain. Scientists discovered giant viruses only in the last decade, so there is still much to learn.

There's no need to stock up on hand sanitizer and tissues just yet though. The Pandoravirus only lives underwater and is not considered a threat to human health.

"This is not going to cause any kind of widespread and acute illness or epidemic or anything," Eugene Koonin of the National Institutes of Health tells NPR.