Sadly Marimo moss balls are in danger and have been for a while. The Aquarium hobby is an unlikely yet surprising champion in the conservation of them. They are in fact not an aquatic moss, but a species of macro algae, and some marimo balls have been known to live for over 100 years if kept properly. They get their round ball shape by tumbling under water like tumble weeds do in the dessert. They even produce extra pearling (or oxygen bubbles) to promote buoyancy in the morning to help them float and grab up more sunlight durring day time hours and then slowly float back down in the evening and rest at the bottom.