A molecular genetic key to the unionids of French Creek, Pennsylvania,
an Allegheny River tributary, is presented here. The key is an integr
al part of a new approach to identifying unionid glochidia larvae atta
ched to host fishes in the drainage. Working with tissue from adult un
ionids, we used the polymerase chain reaction (PCR) followed by restri
ction enzyme digests to find species-specific genetic ''fingerprints''
for the 25 species in the drainage. We have demonstrated the utility
of the key by using it to identify 70 glochidia attached to fishes col
lected in the French Creek drainage.