There are two types...The ones at petco are moss wrapped around a styro cork...The other type are morimo ball replicas...Actual morimo balls are endangered and illegal to keep. The "replicas" are made by hand rolling the same algae that morimo balls are made of into a ball...It is essentially the same thing that happens to form them naturally, only much faster. Long story short, both types are cool to keep, and need next to no light at all.