Pistolgrips are easy to identify, with their shell shaped like a checkered gunstock, with its unique, turned-down edge. In Missouri, they are widespread, living in small streams to large rivers with moderate current in a wide variety of substrates.
Externally, the pistolgrip's shell is heavy, compressed, and elongate; it is covered with pustules; it has a pronounced, knobby posterior ridge with flutings and folds extending to the margin. The umbo (beak) is slightly elevated above the hinge line and is turned forward. The periostracum (thin outer layer) is light green to brown in juveniles and brown or black in adults.
Inside the shell, the beak cavity is moderately deep; the pseudocardinal teeth are large and serrate; the lateral teeth are long, straight, and heavy; the nacre (mother-of-pearl layer) is usually white, iridescent posteriorly.
For a fuller introduction to Missouri’s native freshwater mussels, and to learn the terms for their anatomy, see their group page.
Similar species: In Missouri, the Gulf mapleleaf (Quadrula nobilis) and the rabbitsfoot (Theliderma cylindrica, syn. Quadrula cylindrica cylindrica) are most similar.
Adult length: 4–8 inches.
Widespread, sometimes locally common.
Habitat and Conservation
The pistolgrip occurs in small streams to medium and large rivers with moderate current in stable gravel and sand or mud. It has been found on almost any kind of substrate.
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
Common, although degrading water quality and watershed destabilization interfere with the survival of this and all freshwater mussels.
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. The tiny mussel eventually breaks away and floats to the bottom of the stream, and the cycle repeats.
For its larval hosts, the pistolgrip uses mainly catfish, namely the yellow, brown, and black bullheads, the flathead catfish, and the channel catfish, but it has also been recorded using a few types of minnows, a darter, and the western mosquitofish.
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, including this species, were an important resource historically for button manufacture. Some species are still commercially important in the cultured pearl and jewelry industries.
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.
