I found these organisms recently (mid april) during a pond dipping session with school kids at our local nature reserve. I have no idea what they are, they have no legs and appear to be fringed with a ring of 'short tentacles' /tubes(?). they don't move and I can't discern other features - size is about 3 x 5 mm. I have seen them before. The pond is shallow (from a foot to a yard in places) with lots of dead vegetation, probably eutrophic.
All suggestions gratefully received - currently I'm not even sure which type of reference book to consult.