Someone above said that it could be removed with a standard tool -- but I volunteer at at community bike garage, and as far as I know, there's only one tool that removes this freewheel, and I've never used that tool to remove any other freewheel. You must be able to get this tool from Shimano still, since we have recently had to get a new one. They seem to be made of lead or maybe playdough.
BTW, on the cassette, the cogs are not fixed as you might expect. Instead, in addition to the freewheeling at the BB, each cog freewheels independently of all other cogs. This is usually somewhat difficult to do with your fingers, due to the fact that they are normally encrusted with years of grime.