I can't overstate how much I learned about how hardcore freshwater mussels are during this reporting:

- they can be as small as a quarter or as large as a Frisbee
- their butts are wrapped around their hearts
- their babies are parasitic https://undark.org/2020/04/13/freshwater-mussel-death/

other fun facts:

Up until the 1970s, scientists referred to freshwater mussels as naiads — the nymphs of Greek
mythology who protected the springs, waterfalls or brooks upon which her existence depended.

These days, they go by some incredibly colorful species names, including, but not limited to:
-Orangefoot pimpleback
-Fuzzy pigtoe
-Slippershell
-Finelined pocketbook
-Downy rainbow
-Monkeyface
-Fragile papershell
-Elephantear
-Heelsplitter

SPEAKING OF HEELSPLITTERS:
Johan Boepple, father of North America's mussel-shell
pearl button industry, died from an infection sustained when he stepped and cut his fut on, believe it or not, a heel splitter mussel.

( https://visitmuscatine.com/174/John-F-Boepple)

I also never realized how difficult of patients they can be.

As @UWMadison veterinary epidemiologist Tony Goldberg told me, monitoring a mussel’s health is near-impossible. No heartbeat to measure or temp to take. “The best indicator that a mussel is sick is that it’s dead.”

I also knew they were filter-feeders, but didn't appreciate how GOOD they were at filtering water (up to several liters per hour).

https://www.sciencelearn.org.nz/videos/732-mussels-filtering-water

And finally:

"Living rock" is a phrase a lot of sources use when describing freshwater mussels. But they, and naturalists since the 1800s, have appreciated their understated beauty.

If anyone has any interest in learning more, there are two resources I cannot recommend enough:

The first is veterinarian @abbiergl 's 2017 book, “Immersion,” expertly crafted for a lay audience and a downright delightful read https://islandpress.org/books/immersion 

The second is Wendell Haag's "North American Freshwater Mussels," which is a textbook but totally accessible to anyone interested in ecology or biology.
https://www.cambridge.org/core/books/north-american-freshwater-mussels/0AE8BD455CC9EA7A57552708456B63A3