Polychaete worm

At first glance this looked a beak on a tiny saw fish. But then I realised he was fully flexible and soft. It moved very fast when it saw me (?) but in the photos the segments and sort of brushy legs on each segment are quite clear. The whole creature was a sort of light olive green to grey colour and the brushes a lighter grey to cream shade. It moved fast and seemed to be able to expand and contract the segments, sometimes being thin and long and sometimes being wider and flatter.