Bright green worms on mussel beds? I have never even noticed them before but I guess they are common from the numbers I found and by accounts I have now read in text books. This is the Green Leaf Worm, Eulalia viridis (Linnaeus). It was photographed writhing around with many others on the mussels and barnacles that were encrusting the vertical faces at the base of the Carboniferous limestone cliffs on the north side of Spaniard Rocks at Rhossili Bay, Gower.
The Green Leaf Worm is one of thirty species of marine polychaete worm belonging to the Family Phyllodocidae in Britain. Although not visible in the photograph above, the worm has a row of paddle-like appendages along each side of its body. These are very lively carnivorous worms that secrete loads of mucus which, no doubt, helps them to wriggle around the rocks at low tide looking for food.
The bright orange patch in the photograph above is encrusting sponge. The light green colour on the rock and the barnacles is a coating of microscopic surface algae. The deep pink tufts are red algae. There was a lot of this seaweed attached to the rocks here, often in a distinct band.
You can see from the pictures below how there is rocky shore zonation of the organisms colonising the limestone surface on Spaniard Rocks.
Revision of a post first published 8 May 2009
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Jessica's Nature Blog 
I found one of those green worms down on Mewslade a few years ago. I’ll post a pic of it soon :o)
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Thanks, Chris. It’s odd that I just have never noticed them before this year – I expect I have always been focussing on the shells.
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THANK YOU, Jessica, so much for this informing and well illustrated post.
It helped me solve two Gower seashore mysteries! I have commented on your blog post and added a link from my own Coastcard blog to this one. I hope this is OK by you…
Caroline
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I am pleased you found the information you needed on my blog, Caroline. Thank you for making the link from your Coastcard blog to mine.
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Hi! We saw lots of these green worms on the rocks at Sker Beach today. Never noticed them before!
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I only noticed them myself a couple of years ago. They would seem to be quite common but perhaps are more noticeable at very low tides and are more abundant at certain times of the year.
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