> I've been doing a bit of research but haven't located any information
> about shellfish in Michigan.  Other than the zebra mussel, do we have
> any?  Are they endangered or protected?

Diana,

There are plenty of freshwater shells in your area (lots of bivalves) and a
lot of them are protected.

Try this site for some great pictures of these guys (worldwide but lots in
the states): http://www.inhs.uiuc.edu/~ksc/MusselGenera.html

This site has the shells from North Dakota, but many are probably also found
in your area:
http://www.npwrc.usgs.gov/resource/distr/invert/mollusks/mollusks.htm

And last, this is a site with freshwater shells from Missouri, check it out.
http://courses.smsu.edu/mcb095f/gallery/

All of these are quality sites, but let me warn you up front, there is not
near as much popular literature on freshwater stuff as there is on the more
colorful ocean cousins.  We have some experts on the list who will probably
know of other available sites and who know far more than I about this group
of shells.  By the way, the freshwater mollusks in this country are our most
endangered group of animals and some projections have us loosing 50% of the
species in the near future.

Tom Eichhorst in New Mexico, USA