In reply to Cog:
I've had a look through a couple of the Seasearch books, "Sea Squirts and Sponges of Britain and Ireland" and "Sea Anemones and Corals of Britain and Ireland".
I'm going to stick with Dead Men's Fingers but I'm certainly not any sort of expert regarding marine animals and am happy to be corrected.
The Seasearch books are really good for this sort of stuff but are somewhat specialist publications.
Post edited at 16:51