David Stanwood couldn’t wait to show off his mussels.  

He needn’t have flexed too hard for them to shine. The photos he emailed showed such stunning specimens, gleaming with luminescence, that I told him to come right over, as I was as eager to see them in person as he was to share them.   

On one of his jaunts — this time strolling the perimeter of Seth’s Pond — David found a mess of mussels along the shoreline. While I am quite familiar with our Island’s marine mussels, the freshwater varieties had thus far eluded my attentions.  

But freshwater mussels are both mysterious and marvelous. They have been called “the most imperiled group of organisms in North America,” and are threatened by development, sedimentation of ponds and rivers, climate change, increased temperatures and invasive species.  

Within the boundaries of our Commonwealth, our ponds and rivers boast 12 species of freshwater mussels. Six of these freshwater species are protected by the Massachusetts Endangered Species Act (MESA) and another four require conservation action because of their at-risk status. That leaves two. My friend David happened upon elliptio complanata, one of the two secure species.  

The eastern elliptio is a common and hearty variety It is the type that folks will most often encounter in freshwater rivers and ponds.  They are filter-feeders that can strain up to 15 gallons of water per individual per day.   

Consider: 15 gallons of water per day, for a creature you could hold in the palm of your hand. 

Through an incoming siphon flows a beautiful blend of plankton, algae and bacteria that provides the mussel’s food. Then, back out another siphon go its wastes and other not of interest materials, recycling nutrients back into in the aquatic system.   

Incoming waters serve a second function for these mussels — a reproductive one. In a wild and woolly way that we humans can barely relate to, reproduction for these mussels is a multi-species affair. Male mussels release sperm into the water and the female will take in water with those sex cells to fertilize her eggs. She doesn’t, however, let the eggs go yet. 

The female broods those mini-mussels in her marsupia (not to be confused with Australian mammals) for about a month before she discharges the larval mussels, called glochidia, into the water.  

Those baby freshwater mussels — glochidia — still can’t go it alone. After their mother releases them, they need a host for their next stage. Mussel hosts can include perch, trout, sculpin and other fish. Their best match for reproductive success, however, is the American eel.

Glochidia will attach themselves to the host’s gills (or sometimes other body parts) where they will be encapsulated in the fish’s body. After a couple of weeks in that comfy cavity, the baby proto-mussel will metamorphose into a sand grain-sized juvenile mussel that falls off the fish to the substrate below, and then grow into its adult form. An epic bivalvian journey.   

As is nature’s way, the mussels that survive to adulthood can be preyed upon by raccoons, otters, muskrats, fish and perhaps humans. While most say that freshwater mussels are edible, they are not always a first-choice food. Research suggests that Indigenous people ate freshwater mussels on occasion, more so as an emergency food that would have had to be boiled or well-cooked to soften its tough flesh. One wild foods enthusiast described these mussels as tasting like “mud-flavored latex,” which is enough for me to not consider this species as supper.    

Our taste for admiration might be more well placed in appreciating this mollusk’s longevity of up to a century long, its straining success, or just its prevalence in our ponds. As for David, his latest find is fascinating and a Goliath of a natural wonder.

Suzan Bellincampi is Islands director for Felix Neck Wildlife Sanctuary in Edgartown and the Nantucket Wildlife Sanctuaries. She is also the author of Martha’s Vineyard: A Field Guide to Island Nature and The Nature of Martha’s Vineyard.