Jennifer Kurth, Iowa DNR Biologist: The United States is the hotspot for mussel biodiversity in the whole world. Historically we had about 50 species now we're down to about 45 and five of those are only found in the Mississippi River now. I picked this site here on the Boone River because it has 11 species. I think the highest number we found at any one site inland in inland rivers not counting the Mississippi is 18 so this is doing pretty good. Plus it has three species that are listed by the state of Iowa as threatened.

The plain pocketbook is one of the species that has male and female shell shapes. These are both plain pocketbooks but this one is a female and this one is a male and you can see that the male is a little more pointed here in the siphon end whereas the female is a little more squared off. That gives her a little more room here where for the where the mussels a brooded.

So basically what happens is the male releases his sperm into the water column where it floats downstream and hopefully finds the incurrent siphon of the female the same species. The eggs are fertilized and brooded on special chambers and her gills called marsupium until they reach their larval stage which is called glochidia and then that's the stage at which they need to attach to the fish host.

So that's a female plain pocketbook this is a little bit of her mantle lure sticking out you can see the little eye spot of the fake minnow that she has and if it was out you'd see a tail fin as well and these guys use smallmouth bass and walleye as their fish hosts so she has this little lure to make sure that they get on the right fish because if they attach to the wrong species of fish they won't transform they'll just die. If you were to see this one under water it would be out completely and she actually waves it in the water and then in in between there are where the larval mussels are kept called glochidia. So the walleye or the smallmouth comes down to take a bite and get some of the glochidia in and they can attach the to the gills.

This is a younger pimple back and these guys don't have male and female shell shapes the only way to know which one you have is to open it up and see if it's pregnant. This one is called a three ridge which it's very logically named because it has generally has three to four ridges on the big ridges on the shell so this is another one that likes to use catfish along with the pimple back as their fish host so whereas this one does the minnow lure we believe these guys actually release a chemical attractant kind of like fishermen who go for catfish use stink bait they want to attract the right fish host. So there are some species that are what we call host generalists and will attach to pretty much any fish that swims by and that has an advantage and that you know they can go pretty much anywhere but these guys have evolved that they only use a small group of fish and then they've been adapted so that they have the strategies to make sure they're attracting the right fish host. 

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Gilchrist Foundation