'Marimo' balls washed up on a Sydney Beach. The balls are thought to be an extremely rare species of filamentous green algae. The living organisms are known in Japan as 'Marumo' and Cladophora ball or Lake ball in English, and are sometimes found in freshwater lakes in the Northern Hemisphere. ‘Aegagropilious’ describes the habit of free living algae (algae not attached to rocks) forming into balls. Floating algae balls are thought to be brought ashore by warmer weather and the rough wave conditions.
Roger Dean, Tales from Topographic Oceans, 1973.