[Jensson]

Found this video: https://www.youtube.com/watch?v=v4fHfDrfoJw

Doesn't show movement but shows how they look in the wild, even has a cracked one that is about to form two new balls. You clearly see they aren't just mossy stones, since there are stones lying around with no moss, it is more like a colony of moss balls.

I can easily imagine early life looking like that.