If we had better hearing, and could discern the descants of sea birds, the rhythmic tympani of schools of mollusks, or even the distant harmonics of midges hanging over meadows in the sun, the combined sound might lift us off our feet. Lewis Thomas
I might be misconstruing Mr. Thomas’ remarks, but my simplistic interpretation is that there is much of the world’s creation that we don’t have the sense (physiologically) to appreciate. We can work on that, though. My powers of observation have sharpened over the last few years, supported primarily by time spent in Cades Cove. If you’ve seen my website home page, you might have caught on to that. I did think I was leveling up. However, after a recent EYS (Experience Your Smokies) session, I realized I’ve barely begun to explore the astonishing complexity of the natural world. Our group of 20+ explored a creek habitat, and it was an eye-opener for me. From struggling to pull on waders to seeing the variety of creatures caught in our nets–it was all new to me. One of those specimens is the topic for today.
What Captured My Interest?
Before I answer that question, I must give credit to the Great Smoky Mountains National Park rangers and interns who provided instruction on that particular adventure. Without them, we might not have noticed smaller specimens in the shallows. The fingernail clam, family Sphaeriidae, is quite literally the size of a fingernail, and its minuscule shells don’t scream for attention. These freshwater mollusks are bivalves, along with oysters, mussels, and scallops. A bivalve simply means this soft-bodied invertebrate has an external, two-part, hinged shell. That’s from NOAA, but the marine-life-educated among you already know that. I, on the other hand, had no idea, and assumed it had something to do with heart valves. Don’t be too hard on me. My expertise, such as it is, lies elsewhere. With using words, pretty much.
The clam in question is not endangered in the least, as it occupies space in much of the world. In the U.S. alone, there are more than 40 species. The University of Wisconsin, Milwaukee provides more detail than I found elsewhere, so I’m going with that institution. The population must be well into the millions, perhaps trillions, as fingernail clams, or FnCs as they are known, can live in rivers, streams, and vernal pools. (Note I said “can live”; slow-moving or vernal pools are preferred.) They aren’t as selective as some marine life, and they don’t take up much space. Up to 10,000 can populate a square meter (just over a square yard). Not only that, but they can also “hang out” on plant stems.
Vernal pond - seasonal, shallow, & contains no fish. Safe for breeding mollusks, salamanders, & frogs.
Interesting, and Also Weird
So far, so good, but you haven’t heard the details of their fragile little bodies. They have thin beige shells, smooth to the touch. Ok. But. This little clam has no head. It does have a muscular foot that provides mobility, moving it forward and downward. Its muscles also open and close its shell. And if this isn’t strange enough, there’s more. Fingernail clams have:
- A two-siphon system. This means there are two anatomical tubes – one for breathing/feeding and another to expel waste without having to leave their sand/mud entrenchment. One tube pulls in water containing nutrients and oxygen; the other pushes out used water and waste.
- Lobed gills on the lower side of the shell that assist with equilibrium.
- An inner lining of the shell that is exposed beyond the shell edges. This can detect both light and touch, and avoids both.
- The ability–and apparently requirement–to fertilize their own eggs. Just one clam can generate population growth.
Another interesting factoid is that these clams appear to have developed (on this continent, at least) in the Mississippi drainage basin. How did they make their way to almost every state in the country? One method is their ability to latch onto plants, as previously mentioned. Some of those plants end up traveling with water birds, and these tiny mollusks are unintentional stowaways. Also, sometimes ducks ingest the clam but don’t digest it. If they upchuck it before it clams up permanently, it can start its own family, assuming it lands in a suitable environment. Check out the University of Wisconsin article for more on that and other details not included here. Now it’s time to get to the point of this post.
What's the Purpose of Mollusks?
There are two primary reasons fingernail clams — and probably other mollusks — are good for the environment, according to the Missouri Department of Conservation. The first is that they filter the water as they consume tiny algae and other particles. This clarifies the water.
The second benefit is to provide food for other critters that aren’t put off by their shells. That is, another species, such as a bird, fish, or maybe even a mammal, will consume them. (See prior section for gory details.)
Yes, I devoted more words to describing these little guys than it takes to recognize their contributions. Some achievements speak for themselves, and they may be doing more to clean water than we are.
As to the Message
First, I want to point out that identifying our lifelong purpose is rarely straightforward and can be incredibly difficult to discern. But a 1/2″ mollusk, rarely seen due to its size and preferred environment? It doesn’t even have to think about it. Doesn’t have a head to use for that anyway, but you take my point.
These creatures provide a necessary service in our waterways. The type of mollusk described here depends on no other being to breathe, absorb nutrients, or even to multiply. And yet, simply by existing, it improves conditions for other organisms. We number among those who benefit.
It would be magnificent if humans could embrace that type of life cycle. Well, except for the part where they’re eaten by a duck. I could happily do without that. But I wish I had that same unmistakable understanding of God’s design for my life.
Oh Gayle, I just love how you use your beautiful words to describe these mollusks, but more importantly draw meaning from their lifecycle we could all learn from. Quoting my eloquent friend Gayle: “And yet, simply by existing, it improves conditions for other organisms.” What a lofty goal to ponder and work toward achieving. Thank you!
Fascinating, Gayle! Thanks again for sharing your valuable insights.