Marimo

Marimo (also known as Cladophora ball, moss ball, moss ball pet, or lake ball) is a rare growth form of Aegagropila brownii (a species of filamentous green algae) in which the algae grow into large green spheres with a velvety appearance. The species can be found in a number of lakes and rivers in Japan and Northern Europe.

Colonies of marimo balls are known to form in Japan and Iceland, but their population has been declining.