| I've moved your posts to their own thread so they're more likely to get attention.
The common terms "clams" and "mussels" are pretty much useless. Some people apply them to bivalve mollusks that remain free in the substrate and bivalve mollusks that attach themselves to the substrate, respectively, but the zebra mussel gives lie to this usage. Appearance-wise, the zebra mussel may seem to be a mussel (it even looks like it belongs in the mytilidae family), but it's more closely related to freshwater clams.
I think that zebra mussels would be a really bad idea to put in an aquarium. They are among the most prolific breeders in the world and mollusk larvae can be unhealthy for fish (in large numbers, they can damage the gills). | 
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