Phylum: Chlorophyta   Family: Codiaceae

Codium fragile subsp. atlanticum (A.D. Cotton) P.C. Silva, 1955

Atlantic Green Sponge Fingers; Dead Man's Fingers

Found in rock pools in the mid to lower tidal zones. Originally thought to be an introduction, it is now generally recognised as native. There are a handful of records for the Outer Hebrides of Codium fragile subsp. tomentosoides, now synonymised with Codium fragile subsp. fragile, an invasive introduction largely confined to the south coast of England and west coast of Scotland. Current thinking is, this is one variable species

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