The plain pocketbook is one of the most common and widespread mussels in our state. It lives in creeks to large rivers with quiet to swift current in gravel, sand, and cobble — nearly any substrate except for moving sand.
Externally, the plain pocketbook's shell is large, moderately thick, inflated, rounded to oval, with a blunt posterior end (in males) or a squared-off posterior end (in females). The umbo (beak) is broad and raised above the hinge line. The periostracum (thin outer layer) is smooth, yellow or tan to yellowish green with dark green rays.
Inside the shell, the beak cavity is deep; the pseudocardinal teeth are large, heavy, and serrate; the lateral teeth are high, bladelike, and short; the nacre (mother-of-pearl layer) is white, occasionally pink or salmon.
For a fuller introduction to Missouri’s native freshwater mussels, and to learn the terms for their anatomy, see their group page.
Similar species: The fatmucket’s shell is not as inflated and has a lower umbo. The mucket’s shell is more oval and compressed. The pink mucket, fat pocketbook (Potamilus capax), and bleufer are also similar.
Adult length: 4–7 inches.
Almost statewide; found in all the major river systems in Missouri except for those in the far north and northwest.
Habitat and Conservation
Creeks to large rivers with quiet to swift current in gravel, sand, and cobble — nearly any substrate except for moving sand.
Food
Freshwater mussels consume algae, bacteria, and fine particles of decaying organic matter. They extract nutrients and oxygen from water drawn into the body cavity through a specialized structure called the incurrent siphon; sediment, undigested food, and waste (called pseudofeces) are expelled through the excurrent siphon.
Status
One of the most widespread and common mussels in our state.
Life Cycle
Males release sperm directly into water. Females downstream siphon sperm into the gill chamber, where eggs are fertilized. Eggs mature into larvae (called glochidia), which discharge into the water and attach to host fish — in this species, white crappie, sauger, bluegill, yellow perch, and several more.
In this and other mussels in genus Lampsilis, the mantle flaps resemble a fish, which lures a host fish close enough for the larval mussels to attach. After being attached long enough to develop sufficiently, the tiny mussel eventually breaks away and floats to the bottom of the stream, and the cycle repeats.
Human Connections
Mussels play important roles in maintaining the health of Missouri’s water resources:
- As food for fish, they are important for Missouri’s fisheries. Small mammals and some birds eat them, as well.
- They filter algae, bacteria, and other particles from the water, improving water quality and cycling nutrients and energy in streams and lakes. Clean water is necessary for people and nature.
- Because mussels are sensitive to habitat disturbance and pollution, they are good indicators of the overall health of aquatic ecosystems and water quality.
The shells of several types of mussels were an important resource historically for button manufacture. Some species are still commercially important in the cultured pearl and jewelry industries. This species was important in the button industry and is also valuable to the polished chip industry.
Ecosystem Connections
Native freshwater mussels provide vital functions in aquatic ecosystems:
- They are an important food source for many species of fish, wildlife, and other invertebrates.
- Their shells, both while the animal is alive and after it dies, provide habitat for other organisms.
- As filter feeders, individual mussels can filter a significant amount of water per day, but not all of what they remove is eaten. What they don’t eat is combined with mucus into packets. These pseudofeces packets are eaten by some fish and invertebrates.
Freshwater mussels depend on healthy populations of certain types of fish to complete their life cycle. Although as larvae they temporarily parasitize these fish, the harm to the fish is negligible.
