Phylum: Rhodophyta   Family: Bonnemaisoniaceae

Asparagopsis armata Harvey, 1855

Harpoon Weed

The gametangial plant is found on the west coast of Ireland and around the Cornish coast. The tetrasporangial phase has a much larger distribution from western Scotland to the Northern Isles

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