Phylum: Ochrophyta   Family: Chordariaceae

Myrionema strangulans Greville, 1827

A brown epiphyte on species of Ulva, usually no more than 2 mm in diameter, often confluent. Fertile structures grow vertically from the central part. Not often reported but thought to be common

References: 
Newton (1931) - A Handbook of the British Seaweeds;
Fletcher - Seaweeds of the British Isles, Volume 3 Fucophyceae (Phaeophyceae), Part 1