Unsure of this most likely phyllodoce worm. One for you Chris, etc. Not the best of pics again but I hope to get better with time. Hoping the highlighted pics help.
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Is it possible to make sense of this? 1st you say it's most likely Phyllodoce worm, 2ndly there's nothing to be made out in the picture, & 3rdly you ID it as most likely Eumida etc. Why not get your other worm right 1st, http://www.ispot.org.uk/node/342925 ,Which is obviously not Sabellaria & there's nothing else it could be but Phyllodoce
Why ask me when you've ignored my last ID?
Looks like a polynoid scaleworm to me, with the scales on the left either missing or being regrown
Lat/Lng: 51.3838, 1.319
OS grid ref: TR310702
lower eulittoral/sublittoral area, under chalk boulder.