A P.S. to my prior post:
 
You commented:
 
> (The deepsea environment is the
> largest one on the planet; the freshwater biome is comparatively small.)
 
Ah, that's the rub.  I expect our theories of evolution to be overturned
as we explore the largest of earthly environs - the deep sea.  We have
no idea what awaits us there.
 
Sylvia in Alabama