Phylum: Chlorophyta   Family: Pithophoraceae

Aegagropila brownii  (Dillwyn) F.T. Kützing 1854

Marimo moss ball

A misnomer as they are not moss but an alga. They grow in freshwater lakes and lochs in Scotland, Estonia, Iceland, Japan and Australia. They grow very slowly on the bed of the lochs and form balls as they roll around with water movement. Storms can wash them up on the shore in large numbers.

References: 
John, D.M., Whitton, B.A. & Brook, A.J. (2011 second edition) The Freshwater Algal Flora of the British Isles.
Kützing, F.T. (1854) Tabulae phycologicae; oder, Abbildungen der Tange.