Phylum: Rhodophyta   Family: Rhodomelaceae

Vertebrata fucoides  (Hudson) Kuntze, 1891

Black Siphon Weed

A common species that grows on many different substrata. Found from the intertidal to about 20 meters

References: 
Maggs & Hommersand (1993) Seaweeds of the British Isles, Volume 1 Rhodophyta, Part 3A Ceramiales
Bunker, Brodie, Maggs & Bunker (2017) Seaweeds of Britain and Ireland