Phylum: Ochrophyta   Family: Chordariaceae

Elachista fucicola (Velley) Areschoug, 1842

Tiny Wrack Bush

A common epiphyte of Fucus species, forming filamentous cushions about 15 mm across. In the lower intertidal region

References: 
Bunker, Brodie, Maggs & Bunker (2017) - Seaweeds of Britain and Ireland;
Newton (1931) - A Handbook of the British Seaweeds