Moss Balls or marimo (Japanese for “ball seaweed”) is a species of filamentous green algae named Aegagropila linnaei that grow into large green balls with a velvety appearance of 12 to 30 cm across.
Marimos are known to occur only in Iceland, Scotland and Japan, primarily Lake Akan in Japan and Lake Mývatn in Iceland.
The algal filaments grow in all directions from the centre of the ball, laying the foundation for the spherical form. The gentle wave action on the lake bed frequently turns them over maintaining the spherical shape and ensuring that they can photosynthesize no matter which side is turned upwards.
In Japan the marimo is a natural treasure while in Iceland they are a protected species.