Phylum: Chlorophyta   Family: Ulvaceae

Ulva compressa Linnaeus, 1753

Thread Weed; Tape Weed

A branched thallus, tubular but flattened. In rock pools prefering the middle to upper shore where some protection can be had from storms and wave action

References: 
Fish & Fish (2011) - A Student's Guide to the Seashore;
Bunker, et al - Seaweeds of Britain and Ireland;
Brodie, et al - Green Seaweeds of Britain and Ireland