Phylum: Rhodophyta   Family: Bonnemaisoniaceae

Bonnemaisonia hamifera Hariot, 1891

Bonnemaison's Hook Weed

A multi-branched alga which develops hook-like growths used to attach to rocks and other seaweeds as an epiphyte. The tetrasporophyte was originally thought of as a separate species and given the name Trailliella intricata but later research shows it as fragmentation of the main plant

References: 
Bunker, Brodie, Maggs & Bunker (2017) - Seaweeds of Britain and Ireland;
Dixon & Irvine - Seaweeds of the British Isles, Volume 1 Rhodophyta, Part 1 Introduction, Nemaliales, Gigartinales