"glass" or "ghost" shrimp are rather broad terms that are used to describe clear or translucent shrimp. Here in NW Florida, both the saltwater and freshwater variety are common. The ones I find in our bays or estuaries are stockier (thicker limbs) and usually grow a little bigger (2" or so main body length, antennae vary in length) and have some light brown markings on them from time to time. The freshwater variety I find in rivers and swamps of the same size will have much thinner limbs and will often be completely clear.
Palaemonetes sp., what we most commonly get in our LFS's, can survive in marine conditions if acclimated slowly, but this is more of an adaptation for living in brackish areas and will not live for long if not reintroduced to freshwater. If you were to go out and find some of the saltwater variety in the wild, or get some from a saltwater system at your LFS, I suspect they would do well for a couple of months or so. Some I had in my tank lasted for about two months but I suspect that they were already aged in the wild since they were fairly large for a glass shrimp.
