Sponges may look like plants, but they’re animals—some of the longest-lived on Earth, with a few living more than 10,000 years.

They’re also the least evolutionarily advanced creatures on the planet. But new accidental findings may show we’ve underestimated them.

Sponges evolved more than 500 million years ago, flourished through Earth’s great extinction events, and have endured ever since.

Today there are 6,000 known species and new ones being identified regularly.

Sponges were thought to be unresponsive to outside stimuli and, well, very plantlike. But that changed when it was revealed that sponges could move.

Scientists studying undersea vents in one of the least hospitable places on Earth, in the cold blackness a mile beneath Arctic ice, found thousands of sponges living in the warmer water near the thermal vents.

They set up specialized photography to look at vent activity but were amazed to see something else. The sponges were scuttling—very slowly—across the sea floor.

Most of them had left tracks in the mud behind them, filled with protein crystals called spicules.

Sponges have no muscles or apparent method of mobility. Why and how they do it is still a mystery. But this is a key part of science: looking for one thing and finding something else altogether new.

Perhaps future expeditions will help us understand these and other hidden talents of sponges.