Answers: A, A, A, B, B (real photos)

Called Sukunaarchaeum mirabile – named after a tiny Japanese deity – this strange organism doesn’t fit neatly into biology’s rulebook. It’s not quite a virus, but not a fully independent cell either. Instead, it appears to live in the grey zone between life and not-life.

Scientists from Canada and Japan stumbled on it while analyzing DNA from a marine plankton species. Within the data, they found a genetic sequence unlike anything they’d seen before. Closer analysis showed that Sukunaarchaeum belongs to the domain Archaea – ancient microbes that are thought to have given rise to all complex life, including us.

What makes this organism remarkable is its extreme simplicity. Its genome is only 238,000 base pairs long – less than half the size of the smallest known archaeal genome. And yet, Sukunaarchaeum can build its own ribosomes and messenger RNA – machinery needed for protein production that viruses lack.

Still, it can’t survive alone. 

Like a virus, it relies heavily on its host for energy and most metabolic functions. Its stripped-down genome suggests it has evolved to focus almost entirely on replication, outsourcing nearly everything else.

That makes it a biological paradox: part virus, part cell, wholly unique.

The discovery blurs the boundaries scientists have used to define life, and hints that there may be many more hybrid organisms hiding in plain sight – especially in the vast, understudied world of microbial symbiosis.

How many other lifeforms have we missed just because they didn’t fit our categories?

Read the study:

"A cellular entity retaining only its replicative core: Hidden archaeal lineage with an ultra-reduced genome.” bioRxiv, 2 May 2025.

📸Credit: Takuro Nakayama/University of Tsukuba