Phylum: Chlorophyta   Family: Cladophoraceae

Chaetomorpha ligustica  (Kützing) Kützing, 1849

Ligurian Sea Brick Weed

Another ridiculously contrived and verbose common name! Very common within the intertidal zone, especially the upper shore with lower salinity. Can be anchored or free-floating, often in large masses

References: 
Brodie, Maggs & John (2007) - Green Seaweeds of Britain and Ireland;
Bunker, Brodie, Maggs & Bunker (2017) - Seaweeds of Britain and Ireland