A bizarre tentacled microbe discovered on the floor of the Pacific Ocean may help explain the origins of complex life on this planet and solve one of the deepest mysteries in biology, scientists reported on Wednesday.

Two billion years ago, simple cells gave rise to far more complex cells. Biologists have struggled for decades to learn how it happened.

Scientists have long known that there must have been predecessors along the evolutionary road. But to judge from the fossil record, complex cells simply appeared out of nowhere.

The new species, called Prometheoarchaeum, turns out to be just such a transitional form, helping to explain the origins of all animals, plants, fungi — and, of course, humans. The research was reported in the journal Nature.