Phylum: Ochrophyta   Family: Chordariaceae

Chorda filum (Linnaeus) Stackhouse, 1797

Mermaid's Tresses; Sea Lace; Dead Man's Rope

Bootlace Weed is yet another common name for this alga. The fronds are unbranched and can reach considerable lengths. In summer they are clothed in dense translucent hairs. Common in sheltered areas of the lower intertidal

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