(very subtle : ) )
Well, they say Sharks haven't 'evolved' for millions(tens/hundreds/ of?) years. Which isn't really true, but is as true as the idea this fish hasn't evolved.
I imagine it used to grow much larger. As far as 'adaptive pressure', the pressure only comes if something threatens the viability of a species. What would these things have to fear at that depth ?
For what it’s worth, the list of sharks whose viability is threatened is somewhat long:
http://en.wikipedia.org/wiki/List_of_threatened_sharks
As far as I know, they don’t evolve, no matter how threatened they may be. Weird.