Hi Steve,
 
The two time-honored techniques for loostening the columellar
attachments of gastropods, prior to removal of the soft parts from
the shell, are boiling and freezing/thawing.  Both work well for a
shell collector's purposes.  However, shell collectors are not
usually concerned about keeping the "body" intact, just getting it
out; and neither method guarantees that the entire soft parts will
come out intact.  The outer, more muscular parts usually come out
intact, but as often as not the soft glandular parts in the spire
break off and have to be flushed out with a high pressure stream of
water.  Still, the wider and less numerous the whorls, the better the
chances of extracting it intact.  Such "open" shells as Polinices and
Littorina work pretty well.  Multi-whorled forms like Turris and
Terebra do not.  I'd guess that Tegula should not be too difficult.
At least some of them should come out intact after boiling.  If you
are really lucky, you might be able to shake them out or flush them
out intact.  But usually it is necessary to hook them with a bent pin
or a dental tool inserted into the foot, and pull them out.  Remove
them with a gentle twisting action - don't pull straight out.  (Kind
of "unscrew" them from the shell).  And do it while they are still
warm.  After cooling, they are tougher.
 
Paul M.