It may be a couple of days before I identify this one (assuming that it doesn't follow the usual pattern and have someone successfully identify it within a matter of minutes). I'm not entirely sure of the actual size of the organism shown (why the hell don't invertebrate palaeontologists at least use scale bars?) but I think it's a couple of millimetres long.
Update: The identity of this organism is now available here. Figure from Frýda & Blodgett (1998).